Valve rectifier circuit and how it works.

This looks horribly intelligent.

Which means (by inference) that my coconut macaroon is fading into the sunset.

On the plus side, it’s not impossible I might get a laugh out of this. Not likely, just not impossible.

Onwards and upwards, bull by the horns, goldfish by the goolies……maybe not that…..

The first thing we need to supply our amp is something to plug into the socket on the wall. On the end of this cable, we go into an IEC (kettle) connector, and this has a line voltage, a neutral, and an earth. The line voltage and neutral connect to the mains transformer ‘primary winding’. This ‘primary winding’ is quite sensibly named. In a world of electronics bullshit, you should hang onto anything that might be sensible. Because there’s not much of it about.

This primary winding is the first thing that the mains voltage sees (so it is primary, or first) and it’s a winding, because it’s a long length of copper wire, wound around some metal former. In the drawing, that primary winding is represented by the block marked 240 volt. Also wound onto this same former is another (sometimes many) more lengths of wire. This is the secondary side of the transformer, and in this case we have two HT (stands for ‘high tension’ or ‘high voltage’) windings which supply the two anodes of the rectifier valve. American for ‘anode’ is ‘plate’. But this doesn’t make all that much sense because the cathode is still ‘the cathode’ in American. Don’t ask me??? We also have a heater winding, which is much lower voltage (5volts or 6.3 volts usually, depending on the valve. This heater winding supplies the rectifier valve heater (and possibly other valve heaters.) The property of ‘induction’ enables the transformer to function. The ac voltage applied to the primary winding has some fraction of that voltage ‘induced’ in the secondary winding, which is why a voltage appears at the secondary output without there being any direct connection between the windings.

The heater of the valve often (not always though) is completely separate electrically from the operation of the valve. All it does is heat the cathode.

Here we get to actually how the valve rectifier (and nearly all valves actually) works. By heating the cathode (usually made of a tube of copper with the heater inside it) we excite the free negative electrons on the cathode. I knew we would get to something exciting eventually. The copper cathode is often coated with something like boron, which gives off a lot more free electrons than copper, so making the valve more efficient.

This does next to nothing at all, other than to create a ‘space cloud’ which is a cloud of electrons that surrounds the cathode. However, if then we switch on mains voltage, the secondary of the transformer supplies a high voltage to the anodes, which is positive in one direction. Positive attracts negative, which means that the electrons from the space cloud are drawn towards the anode when it is positive. This has now begun an electron flow from cathode to anode (but only when the anode is on its positive cycle).  Conventional current flow is actually the opposite (positive to negative), because electron flow is negatively charged.

So what we have now is positive voltage appearing at the cathode (marked HT dc out).

On the end of this terminal, we have to provide smoothing for the HT output. That voltage is not usable as it is. So we will look at the choices of smoothing circuits next.

Tea. And not many laughs. Sadly.

 

Valve rectifier?…..solid state rectifier?????

Further to the amp design series. This is part three. If I can get to three without suffering brain fade there must be a slim chance I might know something useful. Eh?

a) So what’s the difference? b) Is there a difference? c) Will I notice a difference?

a) One uses a valve. Duh.

b) Not if you’re deaf.

c) See above…..and…..some people wouldn’t notice a difference if a herd of wildebeest stampeded through their kitchen.

A rectifier of any sort has one purpose, and that is to convert (rectify) an ac (alternating) current/voltage to a dc (direct) current/ voltage. But the valve rectifier has certain properties that the solid state rectifier doesn’t. From a point of view of how it affects the sound, the valve rectifier has the property of ‘sag’. I know how it feels. The valve itself has an internal impedance, and what that means is that the current path from anode to cathode (the conducting direction) isn’t a short circuit, it has a certain resistance. (Impedance, strictly speaking.)

This is a very complex characteristic and varies from valve to valve in imponderable ways. This will not endear the rectifier valve to the digital fraternity. They like to put these numbers into this black box and it does this. Every time. No valve will do that, because the valve is a physical device and as such every one is different (within certain tolerances). Not only does it vary from valve to valve, but also depending on the current it is drawing, how hot it is, what is the smoothing arrangement on the dc side. And what day of the week it is, for all I know?

The characteristic of ‘sag’ in the rectifier, means that as the valve takes more current, the output voltage tends to drop, which tends to limit the output of the amp it is supplying, so providing compression. This is not a simple compression. It is affected by frequency, amplitude, phase angle, power amp loading, even speaker impedances. So far as I know, there is no compression circuit that can simulate this form of compression, it is not very predictable and varies (as we’ve already noted) from valve to valve.

A solid state rectifier, on the other hand, has very little impedance in the forward direction. It will run itself without varying the output voltage, to destruction. So it does not compress, and has no sag factor. This is a big difference, as any guitarist will tell you who has wound up a valve amp with a valve rectifier.

But there is a downside to the valve rectifier. It’s expensive and complicated. It needs, for a start, an extra valve base. It also needs a transformer that will give a heater supply voltage for the valve, which is often a different voltage to rest of the amp heaters. In the case of a GZ32 or GZ34 or 5Y4….etc….5 volts. This means that the mains transformer has to have an extra winding to supply this voltage.

You don’t need any of those things for a solid state rectifier circuit. Just two (or four) diodes, or a bridge rectifier. Nevertheless, our amp (should it ever get to that state) will have a valve rectifier. If we keep it small, say 15 watts  rms, we can do the valve rectification with an EZ80 or EZ81. ….So what?…..ah well….these valves have 6.3 volt heaters, so the mains transformer is much simpler; we don’t need a separate 5 volt supply.

So we’ve actually made a decision. Which is quite something in a life of doing my best to avoid them. We use an EZ rectifier valve and design the output to be around 15 watts rms. And that solves another decision. If the amp is going to be some variation on class AB (we’ll look into this a bit further into the proceedings), it is likely to be using a pair of EL84′s. Not unlike the Vox AC 15, or the Watkins Dominator.

The thick plottens………..

Tea! Macaroon! Oh yessssss!

The Second One in the amp design series.

The general idea in designing/ inventing anything at all, is to get together some wonderful ideas, build them, and then find out why it don’t work. Unless you use a Computer Aided Design piece of soft brain (sorry, software), in which case you can get it to virtually design it, virtually build it, virtually test it, and come up with something you can then virtually poke around with until you get something new. Except it won’t be, because the intuitive human input  has been relegated to accidental poking about and the imagination relegated to accountancy and marketing.

I am not, then, very likely to be a CAD person. In which case I shall have to think a bit. Oh dear.

We’ll start with the power supply. “Why would you do that?” you might enquire. Because if we get that wrong I am not going to get a macaroon. If that part of it is less than it should be, the rest of the amp is unlikely to be worth plugging in. So what do we want from a power supply? At its most basic, some device that takes the ac mains (240-250 volts in UK) and converts it to a useable dc voltage for the electronics. There is little difference in that requirement whether you are supplying a semiconductor (solid state, transistor; call it what you like) or valve circuit. The difference is that semiconductors tend to be higher current, lower voltage, and valves tend to want the opposite. So a power valve will be likely to have several hundred volts at the anode, whereas a semiconductor amp will need voltages of less than hundred volts. The actual voltages depend on the power output of the amp. The power transistors will put out amps, and the power valves, tens (or maybe a few hundred) milliamps.

Clearly an over simplification, and the actual figures will be dependent on the sort of power rating of the amp. But it at least illustrates the general principle.

There are two different possibilities for the power supply, and the main difference between those alternatives is in the way the incoming ac voltage is rectified.

 

 

This is a basic arrangement for a full wave rectifier circuit using solid state diodes. It could also be a bridge rectifier arrangement, but the result is the same, so we will stick with this one.

A diode will only conduct in one direction, and the transformer’s job is change the 240 volt input to a useful voltage for the amp to work with. The primary side is the 240 volt input and the secondary is centre tapped, which enables the ends of that winding to act in opposition. That means that when the voltage increases at one end, (with respect to the grounded centre tap) the other end decreases. This enables the diodes to conduct alternately in their forward direction, so producing a dc voltage from the ac input.

All this sounds fine and dandy, but the output is like a rowboat on a ski jump. Not smooth in other words. And therefore not useable for the amp, as it stands, because what you would hear most is a 100hz buzz. Most tunes really need a bit more than that.

So far there is no difference between that which the valve amp requires from a power supply and that of a transistor amp. The difference comes in with voltage/current requirement, and that brings in a big possibility with the valve amp. It can use valve rectification, and the solid state amp does not have that option.

In the next blog we shall consider the why’s of that, and what the differences are.

And just in case you might think  I’ve turned sensible, I shall, especially for you, dear reader, come up with some really, really daft ones.

Have a good macaroon…..I mean…..day.

 

 

This might be a bit of a shock

…..and surely will be if you were silly enough to trudge through the last, extremely daft, post.

I have mentioned (probably many times) my ambition to design an amp. After a year or so I’ve got a bit further with this ambition. It is called ‘A Guitar Amplifier’. Slick, eh? At that rate of progress the second great flood will have swept the planet before I get down to soldering something. At least you will know who it is paddling the ‘Guitar Amplifier’ across the frozen wastes  of Biggleswade.

My second idea (on a roll, here) is to entertain you, oh erudite blog readers, with a sequence of blogs that will take you from the very first stages of amp design, though to the…erm….very second stages, etc, etc.

Alright, let’s make start. Questions first, answers second.

What level of marketing bullshit are we going for? Zero, because I don’t care if I sell any, because it’s for me, and because it’s just a fascinating thing to do, to build something that skirts around all the stuff that doesn’t work (or doesn’t work very well) and takes the stuff that does work to another level. Hopefully.

Another question. What colour is it? Don’t care. Next question?

Valve or semiconductor or hybrid of some sort? This sounds a bit serious, and I can see my macaroon dwindling. To come up with an answer to this one, we have to consider what a Guitar Amplifier actually does. The text book answer for this is that an amplifier makes whatever it is going in, bigger when it goes out. It has the property of gain, in other words. But in my Guitar Amplifier, this is only part of the story. A semiconductor of more or less any sort will produce (all things being equal) an output very close to the original input, but bigger, because its characteristics are close to being linear. A valve will rarely do this, it will add things; harmonics for instance, because its characteristics are rarely linear; and also certain sustain capabilities, because it will tend to ring in some degree. A guitar player might find this very attractive, or obnoxious. Two guitar players might have both opinions, it is a subjective thing. As this is for me, I can poke around with it until it sounds as I would like it. Bearing that in mind, I am very likely to produce, at the end of this process, something based on valves.

And CERTAINLY NOT a ‘digital modelling amp’. This is something that can sound like everything but not much like anything.

There we are, a start. Zen saying “A thousand mile journey starts with one step”. But so does a journey to your front door. Doesn’t it?

Tea. Macaroon. But only because it’s nearly New Year. I preferred the ‘Charter Flight’ blog. I got a laugh (and a legitimate macaroon) out of that.

 

Space ships, and how to fix ‘em……not really.

 

If a space ship did turn up on my bench, however, I would definitely have a go at fixing it. The old ones are alright to have a go at fixing. A screwdriver a hammer and a pair of pliers and you should be ok with all but the neutrino beam focus plates. You would need a bigger hammer for that.

However, if your client’s space ship was but a few years out of its sell by date, chances are its engine management pcb is dud. Problem. The engine management pcb  will cost you about forty times what the space ship is worth. Which is nothing at all if the thing won’t go. And forty over zero (anything over zero for that matter) equals infinity, which is more or less the figure Barclays will charge on your unagreed overdraft.

We are now in serious waters, as the infinite bank rate (not when you are waiting for your interest payout of course. That is zero over infinity which is, technically speaking, in the shit.) will cost you the savings you might have accrued thoughout several lifetimes on the wheel of Karma. So beware when taking in any space ship that dates from 1990 or so.

And now for your Christmas boredom………

 

                                                                                         Charter Flight.

 

 

 

            Through the screen image breakup, she didn’t look good. The fortunate hundred million miles between them meant he couldn’t see her ‘in the flesh’, where she looked a lot worse.

            “Can you not screech into the audio metaboliser? Please!” The distant audio metaboliser she screeched into cringed; she passed a damp flipper across her fevered brow.

            “Is this better?” whispered the brow-beaten prospective client for Canary Charter Flights Inc. A pained moan from a hundred million miles away said it wasn’t.

            “Try it again from across the room” she insisted. “…And walk quietly please.” The debauchery of the night before had taken a heavy toll on the suffering receptionist/metabolist; NGTOP tip-toed backwards until he felt his shoulders against the cold plaster of the furthest wall.

            “How’s this?” he hissed in a stagey whisper that sliced like a Turkish cymbal through the lady’s hangover. She rattled down a half bottle of aspirin.

            “Try outside.”

            “I’d rather not,” said the part time detective cum alien, an irascible edge beginning to cut through.

            “Why not?” She spluttered through a mouthful of the rest of the aspirin bottle.

            “Because I’m twenty three floors up; and” said NGTOP, well on his way to screeching the ceiling down,

            “And?”

            “And,” he bellowed, “I don’t want to broadcast this conversation on a loud-hailer because I’m on a Top Secret Mission. Ooops.” NGTOP dropped to his knees and looked furtively about his flat. Satisfied that his mission was still as top secret as it had been prior to his blasting its classified status from the tower block rooftop, he returned, at no more than a whisper, to his abortive conversation with the unfortunate lady.

After his near death experience with Derek Modley and his by now famous Dangerous Greenhouse, NGTOP had decided on an identity and career change. Not that he was convincingly the possessor of either of those things before the changes. The move into the private investigator business had seemed a relatively safe option, compared with his recent brush with the Colyster Generator and Universal destruction.

“Maybe I’ll try another charter company. It was the ‘Canary Charter Flights go Cheep’ advertising campaign that swung it for me. It’s just that there’s nobody else this cheap.” He assumed the Ben Marlin persona that he had recently invented.

            “I’ll confirm our conversation by cyber-trace, Mr. NG…err…Thingy” said the telephonist, unwilling to risk another encounter with strangulation on NGTOP’s unpronounceable name.  

            “What, all of it? No, no. Don’t do that!” NGTOP did summersaults.

            “Only the booking arrangements Mr. err…Thingy, that’s all. It will lessen the risk of a distant suicide. Mine.”

            The bucket of colour that had drained from Marlin’s face filled up again, assuming its traditional tinge of puce while the gangrenous shades of the far distant telephonist scattered across the screen.

            “Marlin!” A corrosive voice from the corridor outside rotted the carpet. NGTOP’s adopted pseudonym had saved many an alien throat from strangulation by epiglottis reef knot. Such were the pronunciation impossibilities of the name of NGTOP. 

            “Marlin!” another voice, scarcely less musical than the first, elaborated. “We know you’re in there.” There would be little point in verbally stripping the paint off his letter box were he somewhere else, thought Ben Marlin, aka NGTOP. And he knew exactly what they wanted. Why they wanted it, was an answer he felt he might more likely stumble across in a mental institution. There seemed no sane explanation.

            “We’ve got the Modley guy. He knows all about the Colyster Generator. So we’ve got all the information we need.”

            Ben (NGTOP) mused on this for second. There seemed to be two flaws in their argument. First, Derek Modley knew sod all about the Colyster Generator; that was even though he’d built one by accident. Secondly, the McNasty Brothers’ numeracy went little further than the tally of their collective finger count. The idea that they might have a brain cell between them to wrestle with the quantum physics of the Colyster Black Hole Theorem was far-fetched.    

The hinges of the door flew across the room just ahead of a plasma ray beam, and Marlin sprinted for the exit and onto the balcony where he jumped off into the darkness. On his way down he found time in his busy schedule to look back at the half dozen pig-ugly black trilbies peering over the balcony in the company of Derek, who happened to be suspended over it by his feet; and also to wonder what had possessed him to jump off.

            “We’ll get you, Marlin, and the Generator” shouted he of the acid tonsils, after the plummeting form of Ben Marlin. “Death will be no excuse.”

            Threatened with imminent termination by floor, Ben showed exceptional agility; unprecedented in a life of lethargy. The flash of a grappo-hook split the night as it flew from his sleeve and tore through the decorative tenth floor awning, ‘Massage Parlour and Fish Bar’. Having creatively renamed this as ‘Fish Massage and Barlour Par’, the grappo-hook further rearranged the next six floors awnings into a messy parachute and broke Marlin’s fall by guiding him onto a passing group of carousers.

            “Sorry.” He said unsatisfactorily, as he stood up amid the welter of broken bones that had been his landing pad.       

 

            It had all been in the interests of making few extra bucks on his fee as a part time private detective, by travelling cheap. He drew up at the deep space terminal in the esotruck flaunting his ‘cool guy’ image, stepping out onto the mica shingle in his slick all-in-one grey moonsuit with the suave flashing rubber tassels.  

            “There you go, feller,” said Marlin, sweeping his plastic Credit Toad under the attendant’s nose. The Credit Toad was an extraordinary development of ancient credit card technology. The cornerstone of the barter system which followed the great Fiscal Downfall was the Credit Toad.

            Inside your trusty Credit Toad were all your worldly goods and chattels; compressed to fit into a plastic Toad. Most of these, in the difficult times after the great fiscal collapse of the early twenty-first century, were of manageable size and would stand in nicely for the rubber duck in your bathtub. There were very few people who had to carry theirs around on a truck. There were few enough left whose finances could stretch to the rubber duck, for that matter.

            “Sorry sir, we don’t take Toads,” said the attendant. NGTOP was incensed.

            “You don’t take Toads! You can’t be serious, man.” Actually, the attendant’s attitude was not unreasonable. When retrieving one’s worldly goods from the Toad, the resulting pile of broken glass and twisted metal was often not worth the plastic Toad that had crushed it to smithereens.

            “We’ve had too many receivership issues, sir.”

            The trick with a Credit Toad was never to open it. This was the problem that eventually sank the credit card system but for different reasons. The credit card because there was never anything left in it and the Credit Toad because there was always too much.

            None of this was helpful to Marlin.

            “How about this?” But before Ben could flick back his sleeve, the attendant had revealed two forearms full of ReAltime watches. “Maybe not” said the detective, wondering how he was going to pay for the parking for his flight; preferably before the McNasty brothers arrived.

            “Nobody cares what time it is anyway,” said the attendant; “I’m more into designer tassels. Like the ones on your suit; they’d look good on my hat.” He took his hat off and pushed it into Marlin’s chest. Two minutes later the attendant looked resplendent under his wobbly luminous tassels, and Marlin felt undressed without them. The deal done, NGTOP hefted his luggage and broke into a run for the departure lounge as the McNasty brothers spilled from an aging black stretch limo.      

            “Welcome to Canary Charter Flights, sir.” The lady behind the departure desk looked uncannily like the one on the end of the metaboliser. The hour’s sleep on the warp trip had done her no good at all.

            “Another hangover?” quizzed Ben Marlin as a matter of polite conversation.

            “Uunnggghhh.”

            “Thought as much” Marlin cast a rapid glance over his shoulder at the heavies stampeding across the departure lounge. “Would you mind if I…?”

            “Certainly, Mr. Marlin; please run along to your flight before those morons convert my nice departure lounge into a blood bath using your blood.”

            “You are very kind,” said Ben, spinning on a heel and sprinting towards the door for the takeoff pad.

            “Not at all;” she shouted after NGTOP’s clean pair of heels, “I’d have to clean it up.” Ben Marlin pushed through the exit doors and stopped as if poleaxed.

“Miss; er; miss!” he shouted in a panic.

“Yes?” grated the pained monotone from behind the desk.

“I might be having a mirage; or something. Could you just take a look at the takeoff pad, it seems to have a very large chicken sitting on it.” Marlin’s eyes boggled.

“No it doesn’t,” she said evenly.

“But, honestly, it is very large, it is a chicken and it is sat on the pad. I can see it.”

“No you can’t. It’s a canary.” The disinterested receptionist turned back to potter with the screen on her desk, and Ben Marlin’s mouth wagged up and down like a cat flap in a high wind. A man with a painter’s ladder strolled across to the giant canary, which looked down curiously at the little man.

“Cheep” it said to him, deafeningly. The receptionist shouted through the departure lounge.

“This is Canary Charter Flights, and you did want ‘cheap’. What did you expect?”

Ben Marlin was suddenly distracted by an unwelcome thought. He watched the approach of the ladder with morbid interest.

“How do I, er, sort of, you know, get in it?” Marlin’s vision was not a pretty one.

“Up the ladder to the little pod that’s strapped to her back,” the receptionist was busy pulling on a suit adorned with a plastic tag. The sparse text on the tag looked alarmingly like ‘pilot’, in red capitals. The McNasty brothers stood in the doorway to the takeoff pad, gaping at monstrous bird preening under its wings, clearly preparing for its take off procedure.

“Hey you!” said Monty McNasty, either to something he’d picked up on his shoe, or the receptionist/pilot/telephonist. “There’s a turkey sat on the take off pad.”

“No, there isn’t” said the pilot/ receptionist/ telephonist-turned-bouncer, walking with some attitude towards the exit that the McNastys were gathered around; “it’s a canary!”

She dealt out a few deft chops of her several flippers, and the McNasty brothers found themselves scattered around on a floor formerly used as a grill pan for fatty burgers. She charged through the doors like a falling tower block, and continued across the tarmac, stopping briefly to crane her neck up to the canary; which was fifty feet high if it was an inch.

“Hello Clara,” she said “nice evening for a flight.” Clara, distracted from her spray of millet for a second, uttered an affable if glass-splintering

“Cheep.”

The flight’s sole passenger meanwhile had an excellent vantage point from which to witness the conversation; and no interest in it at all. Ben Marlin was completely absorbed in hanging onto the swaying ladder about thirty feet from the ground. 

“Cheep” said the cheerful bird.

“Don’t do that!” said Marlin as avian vocal cords shook the ladder to its last molecule.

“Cheeep!” It said happily.

“Eeeek!” said Ben.

“Cheep, cheep, cheep!” replied Clara, clearly in raptures with the conversation, whatever it was about. The ladder began a series of bouncing movements as the pilot swarmed up the underside with incredible agility and passed Ben Marlin who appeared to have been nailed to it.

 

The McNasty brothers nursed their injuries in the decimated departure lounge. Monty McNasty fumed while poking at a tender black eye.

“That guy Marlin loused up our last Colyster deal; he’s not going to screw this one up; over my dead body.”

“The Martian Colyster Generator deal will settle those two and put us on easy street. We’ll be in the ‘Designer Asteroid’ belt.” Monty McNasty allowed himself a sneer. “They’re never going to get to Mars on a Canary. The job is in the bag. We’ll book the next flight with ‘Package Tours Inc.’

 

            The single most valuable possession in the Universe was a Colyster Generator. There was not enough money in a whole planetary system to buy one; these things were then, all but impossible to buy. And just as difficult to steal, as transporting the black hole at its core was not something you might manage in a Transit van.

One Colyster Generator could heat an entire dead planet for nothing; and Mars had been converted from a dust bowl to an Eden in the space of a decade or two by the Generator built by Derek Modley.

            Sadly for Derek, he took bad advice on patent issues and signed it away to a plausible guy called Monty McNasty, of ‘McNasty’s Preloved Armaments Inc.’ for a bootleg DVD of ‘Happy Days’.   

 

            Ben Marlin arrived at his seat and found a plain brown envelope on it. Not at that time feeling up to the challenge of a piece of brown paper, he stuffed it in his inside pocket and rummaged around in his bag for his hip flask of ‘Hell’s Dregs’, downing most of it in one. This stuff imbued super-being confidence and the skill levels of a crustacean. Ben was convinced he could fly without actually being able to walk. He fell in a heap in the aisle and took to swimming a front crawl.

            Take-off sobered him up with the cabin bouncing through three hundred and sixty degree rolls as Clara got the hang of it.

            “Captain!” wailed Marlin from the floor/ceiling.

            “What?” replied the telephonist/ receptionist/ bouncer/ pilot/ Captain; who appeared to be having little effect on the course of Clara. 

            “We’re all going to die!”

            The twisting rolls suddenly smoothed and Clara settled into a rhythmic flight not unlike a rowboat on a ski jump. The whistle of wind under Clara’s wings petered into silence and the cabin’s extreme rise and fall flattened out.

            “Can I ask a question, miss?” said Ben Marlin, still untying the knots in his stomach.

            “If you must,” said the Captain tetchily.

            “How do you expect a canary to fly in the vacuum of space?”

            “Clara has three boost stages; breakfast, dinner and tea” said the bored Captain.

            “I don’t understand” said Ben. The extreme G-force of an abrupt acceleration accompanied by a deafening farting noise kicked Marlin between the shoulder blades. “What was that?” he choked, fighting for breath.

“Breakfast” said the Captain.

 

            Back at the terminal, the flight from ‘Package Tours Inc.’ had just arrived and the McNastys stood on the tarmac around a brown paper package.

            “Has everybody gone mad?” remarked Monty McNasty.

            “This one is our mini economy flight; you have to blow it up.” The steward handed over a foot pump.

 

            “This is your assignment” read the note that Marlin had retrieved from his inside pocket. “The Colyster Generator on Mars will be attacked tomorrow: you must protect it at all costs.” Ben Marlin flicked through his regulation issue of ‘Code Cracking for Baboons’ before he realised it wasn’t a code. 

            “Ridiculous” thought Ben Marlin. “Nobody has ever stolen a Colyster Generator; come to that, nobody has ever seen one to know what they might be trying to steal.” The detective read on.

            “The attackers have the conversion kit.” The note went on; Marlin had heard of the conversion kit that converts the Generator into a bomb; the power of which made fusion physics look like popping popcorn. “We believe the intention to be Universal blackmail.”

            NGTOP scratched his head, and turned the note over, the surface of which was as blank as the expression on the detective’s face.

            “Why should anybody want to trade in the whole Universe for a clinker of ash? In what ways could the bomb-terrorists possibly profit? Had they a season ticket for some idyllic afterlife?” NGTOP (aka Marlin) had to concur that blackmail on a vast scale seemed the only plausible purpose. The private dick looked up from his reveries to see the hostess (receptionist/ telephonist/bouncer/pilot/Captain) reeling down the aisle with a tray of drinks and an in-flight meal.

            “For your comfort and delight” she read from the ‘recommended greeting’ sheet; “but discomfort and disgust might be closer to it” she improvised; and handed over the concoction to Marlin. Ben retched and made a break for the toilet.

            He returned to his seat in time to hear;

            “Fasten your seat belts for landing, please.” Ben searched about for a seat belt. “No, ignore that; I forgot this is a budgie flight. Sorry, ‘Budget Flight’. Anyway, the budget flight’s answer to the seat belt is the brown paper bag behind your seat.” There was another short pause. “Please check that this has not been used for, er, anything else, before putting it over your head. Thank you.”  

              Clara’s second booster stage kicked in as a retro rocket, and after being strained through the fibres of his seat, Marlin settled down to being merely terrified out of his stomach. The full complement of passenger and crew being absorbed in the hazards of a Martian landing, the brown paper parcel following entered the Martian atmosphere unnoticed.

 

            The underground labyrinth hummed tunelessly in sympathy with the infinite power of a Colyster Generator in tick-over. The hiss and crackle of an empathy door sent echoes bouncing along convoluted corridors. The creature strode with the brown paper parcel it had collected from lost property, through the door from other dimensions. It stooped and swayed gracefully as if in an undetectable breeze as it stowed the parcel. Its slender limbs flexed in the subtle glow emanating from walls of crystal, as it struggled with the tartan shopping trolley.

            “How do they expect anybody to do a professional job without quality kit?” The Caph cast a withering glance at the little trolley, and turned again to drag it along the corridor. The wheel that wasn’t there scraped unmercifully on the steel floor. “Aagghhh; my teeth!” The Caph swept a delicate aspen hand to its cheek. “Alright, that does it. They can count me out of the next Universe-destroying mission.” It turned back to its course and the trolley resumed its banshee squeal, the Caph mumbling a steady torrent of abuse under its breath.

            It plodded through the endless liquid plasma barriers, each one levelling molecule disintegrators at the Caph; which it ignored. The disintegrators could sense it was there, but beyond that had no sense of what it might be. They made enough noise about it though. After the twenty-third barrier of head-splitting bells, the Caph wearily stretched out its limbs into the endless corridor, yawned, and rummaged in the shopping trolley, carefully avoiding the Colyster detonator wrapped in brown paper, to fish out a parsnip for tea break. It munched meditatively while staring at the opposite crystal wall. Subtle reverberations of a distant door circled confusingly and disturbed the Caph. It stood up, repacked its parsnip, and continued its shambling pace towards the destruction of the Universe.

 

            Ben Marlin gazed down the twisting crystal corridor, trying to make out the strange, willow-like figure in the distance. The plasma barriers made it impossible to focus. He hefted a demoraliser ray from his tartan shopping trolley, levelled it on a forearm and sent a long burst into the length of the corridor.

            “My mum didn’t like me” blubbed the first barrier, utterly demoralised by the ray, ahead of the stream of heart-rending complaints from the succession of barriers. The Caph, way down the corridor, turned towards the commotion.

            “You should go home” it called to NGTOP, “it is dangerous here.”

            “Where is this ‘Home’ I might go to that isn’t dangerous?” enquired NGTOP, not unreasonably. This seemed to be something that the Caph had not much thought about, and it put down the handle of its shopping trolley while considering. Ben Marlin sauntered along without fear. There seemed little point in being terrified as he considered himself as good as dead already.

            “Nice trolley” said the Caph. Ben looked around. It was definitely talking to him. He smiled a wan shadow and pointed down to his shopping trolley for confirmation. “Yes” said the Caph. “Nice. Got all the wheels as well.” Marlin gulped and nodded.

            “Fancy a swap?” asked Marlin tentatively, as he continued to trudge the length of the corridor and up to the Caph. It was dumb ploy to relieve it of the detonator. But then anything dumb enough to consider blowing itself to bits for profit might not notice another dumb ploy.   It swayed a little.

            “This one squeaks,” it said making a suave gesture at its tartan trolley.

            “Nice pattern though.” Ben Marlin listened to himself and thought he’d already made a swap; from average humanoid brain to Lego windmill.

            “Yes it is a nice pattern; how good of you to notice. Unfortunately, it is quite heavy.” The Caph shook its head plaintively.

            “I don’t mind that” quickly interjected the detective, “it will… er…stop me blowing away in high winds.”

            “I am here to destroy your Universe, you know.” The Caph made an apologetic smile. Ben Marlin was a little taken aback by the Caph’s candidness.

            “Well, I’m actually here to stop you. But nobody seems very sure of what you might gain from blowing yourself to bits.” Ben Marlin had discovered the answer to that over the course of his brief conversation. The Caph were in no danger at all from the destruction of this particular Universe. They lived somewhere else entirely.   

            “Your Universe causes a lot of trouble with our TV reception. This Universe makes it impossible for us to follow the story of the ‘Happy Days’ programme. A pained expression crossed its face.

            “I’m not surprised you can’t follow the story in Happy Days. There isn’t one.” Ben Marlin stared up at the Caph’s sylvan form.

            “Oh.” It said. Then it blossomed into a radiant smile. “Are we still on for a swap?”

 

            Ben Marlin, lugging the alien shopping trolley squealing its objections back through winding corridors, couldn’t help but wonder what he might do with a Universe-destroying tartan shopping trolley with one wheel that was giving him a headache. The answer lay around the next bend.

            “We said that death wouldn’t get you off the hook for this one.” Marlin almost walked into the McNasty gang. “We want our shopping trolley back.” The detective’s trolley contained the destruction of the Universe, and to hand that over to a bunch of bent second-hand shopping trolley salesmen seemed less than sensible.

            “This, gentlemen,” said Marlin, having decided to brazen it out “is not what it seems.”

            “We can see you have not treated it with the respect it deserves, Ben Marlin. Where is our wheel?” Monty McNasty pulled out a randomiser-ray with a barrel nearly as long as tartan shopping trolley he pulled it from. “The deal is simple. Give us our trolley back, complete with wheel, or I blow your head off.” The rest of the gang were standing around sheepishly, each with his own trolley, and each sporting a subtly different plaid.

            “Nice.” Said the Caph as it materialised behind the gang, gazing in wonder at the assorted fleet of trolleys. “Don’t fancy a swap, do you?” Monty and the gang were surprised, to be sure, but the boss was quick to get his accountant’s head together.

            “I take it you ain’t big on arithmetic where you come from,” said Monty with a sneer, “we’ve got six trolleys, to your one. What sort of swop is that?” Marlin was fascinated. How was the Caph going to talk its way out of that one?

            “In here,” it said with an air of collusion as it pointed into its shopping trolley, “is the complete set of DVD’s for Happy Days.” It took a gracious bow for the applause that rippled around. It pointed to Ben Marlin. “His has the Colyster Generator detonator in it.”

            A quiet descended. The Brothers McNasty went into a huddle. Monty’s head surfaced briefly.

            “Why don’t I just blow you both to bits and take the trolleys?”

            “Because you’d wipe out the Universe at the same time?” ventured Ben Marlin. This seemed to settle the quandary and Monty McNasty turned from the scrum.

            “O.k. tall guy,” he said to the Caph, “you got a deal.”

 

            It turned out that the Colyster Generator detonator was an out of warranty OEM version that wouldn’t detonate the Caph’s parrot out of its ‘Beano’. Marlin left it outside the departure lounge as a monument to something.

            He checked his Toad for a new deposit. Satisfied that all was in order, he walked across the tarmac to where a very big canary sat, preening.

            “We’re almost ready for your return flight, Mr. Marlin,” said she of the multiple flippers.

            “Cheep!” bellowed Clara. Ben Marlin looked up at the soaring canary with a slight shake of the head.

            “I’ve decided to emigrate to Mars” he said.

                      

                               The End.

             

 

             

 

       

             

             

 

             

     

             

           

           

                                

 

     

 

   

        

  

 

 

      

                              

   

           

 

             

             

             

               

Ampeg BA300…….again.

This is an indication of how incredibly bloody-minded I can be.

This amp belonged to Paddy; he used it as a spare, and so was not in any rush to get it back. But this amp stretched the limits of credibility and patience. Most jobs I turn around in a week, this one took THREE YEARS.

Paddy would turn up from time to time, with various jobs (a Stingray bass, an Ampeg SVT Pro, an Ampeg SVT) and would ask, more or less in passing, how his Ampeg BA300 was coming along.

It was, I would shamefully say, work in progress. That was fairly obvious as it was in a hundred bits on the bench, and, as I mentioned, didn’t move for three years. I use three benches in the workshop, and the BA300 just sat on the middle bench, daring me to repair it. Every spare hour I would go back to it, work through my notes, order further bits. The fault is, it would seem, a common one. It should (don’t know why) switch off if the output power exceeds 300 watts. So if you give your bass a hefty slap, it will switch off, if you are already pumping some power through it.

I think this is quite a daft idea. But it’s double-daft if it switches off when pushing 12 watts out. Or so. This is what Paddy’s amp was happy to do. Why Paddy didn’t actually chuck it over a cliff I’ve no idea, and it is a great compliment to his incredible patience.

At the risk of repeating myself (there is another, earlier and desultory blog on this subject) this is a mosfet, class D amplifier, with bridgemode output. A class D amp has carrier signal (of around 400+ KHz if I remember right) and this is modulated by the audio signal. The modulation in a class D amp can be either frequency or amplitude modulation; this one is frequency modulated. Why anybody would want to modulate it in the first place is a mystery to me. Probably to make sure it switches off at embarrassing moments.

I did replace a hell of a lot of components in this amp (the sign of being lost in a swamp) and every time it made no difference at all. However…..

You need a schematic for this next bit, and I must say that it is not difficult to find them on this amp. SO FLAGS OUT FOR AMPEG. Not everybody is in the Secret Society just yet. To the left of the 2nd page is the dual preamp chip U1 (4558) in which the two op amps are used in cascade. The output from pin 7 sends the analogue signal via R1 to pin 6 of U2 and the other opamp in this package is used to mix the 400+ kHz carrier signal and frequency modulate it. This dual chip is a TL082. YOU CANNOT USE A TL072 (as would often be ok ). In this case, it won’t work.

You don’t want to see a dc voltage at pins 1 or 7 on this chip. I was seriously stuffed with this as I changed the chip I think three times, and each time I got a dc voltage at pin 7. Eventually, you start to think that there is something here that you don’t know about, and assume that this is how it should be. No it isn’t.

Eventually, it turned out that there was a crack in a track on the pcb UNDER THE CHIP. ARRRRGGGGGHHHHH!!!! Even when I had the chip out, you couldn’t see it. I resorted to testing for continuity on all the tracks associated with the U2 chip.

The eventual reason for the fault was that the pcb was too thin and flexed when the vibration hit it. That was my guess, anyway.

I would not wish this repair on anyone.

But I did get a celebratory pair of macaroons. And in the evening, a celebratory Bowmore malt scotch. Did I deserve that one. Oh yes!!!!!

 

‘Tis the Season to be Morbid

Look, I’m sorry, but in my book Scrooge was one of the good guys. Anybody who can blame a ghostly attack on indigestion just can’t be all bad.

Just to show you that I am truly penitent, I’ll sing you a carol.

“In the bleak mid-Waitrose, Asda winds may blow. In the car park at Tesco, people turn to stone.” (Sung to ‘In the Bleak Mid winter’)

As I am over the age of sixteen, I have to prove myself worthy of my next breath. So here’s a list of things that I have fixed over the last three weeks, or so.

1950 Watkins Westminster, Echolette NG51 tape echo, Fender Acoustasonic, Fender Hot Rod Deluxe, Universal Audio valve preamp, Peavey Delta Blues Combo, Orange AD30TC,Trace Elliott 150 bass head, Kef Subwoofer amp, WEM dominator mk3, Sony Pro Walkman, Peavey Deuce,Orange Tiny Terror.

There hasn’t been much action on the blog, and sincere apologies to all those daft enough to read them. In the New Year, there will be astonishing revelations. Can’t for the life me remember what they are…….But certainly related to macaroons. Hopefully.

HAPPY CHRISTMAS from Roger.

 

 

A thank you to Gareth for his Donation to my Macaroon stash!

I didn’t charge Gareth for my perambulations (didn’t think I knew that one, eh?) through his Cornell Romany Pro amp. If I charged folks for not fixing things I would be very well off. Anyway, it turned out that his problems with the amp were not faults, it just didn’t do what he wanted it to, so I didn’t actually fix anything, but spent a lot of time working out how it worked.

Make no mistake, this is a beautifully made amplifier; but I got the feeling in my water that there was some faulty thinking gone into the design of the amp.

Gareth turned up for his amp with a couple of packets of Macaroons! Chocolate and plain. Bliss!!!

So as a small “thank you” I offer this little piece of history of the origination of the macaroon thing.

A long time ago, when I was up to my neck in an industrial apprenticeship, I worked for some time with a hilarious cockney gentleman named Cyril Haffenden. If a problem reared its head, or if he just felt a bit stressed by it all (or any other reason, for that matter) he would pronounce in a loud cockney accent “THAT’S IT! BAGGER IT! A CAPPA CORFFEE AN’ A MACAROON!!!!

That’s where it came from, tempered by poetic license of my own.

Thank you, Gareth.

 

Cornell Romany Pro……had me going for a minute there.

This amp knocked a year or two off my life expectancy, and foot or two off my hairline.

A schematic is the most valuable attribute to repairing an amp; with a working brain cell running a close second. I’m saying nothing about the latter, but the Romany Pro does not subscribe to the former. I found an owner’s manual (for the Romany) which told me where the knobs and switches were, but not much else. Back to the Secret Society again, then.

Nearly all valve amps have a working topography of:-  preamp stage(s) (usually ECC83 based valves) into a phase splitter (if it’s a push-pull class AB amp) and into a push-pull output stage. The phase splitter arranges the signal to the output valves so that one half goes positive while the other goes negative. This results in the push-pull of the output stage.

This Romany Pro was different, and it took a while for me to figure out how it could work. Everything I tested, from the phase splitter on, was in phase. Without going into too much detail, that can’t work because the output transformer tries to sum two identical in-phase signals the resultant of which is zero. A zero watt amp is never going to catch on.

Then I noticed that the phase splitter, isn’t. It doesn’t (as the usual arrangement does) split the phase, it just puts identical signals to the output valves. The only way this can work is by reversing one of the secondary windings of the output transformer. I’ve no idea why people like Mullard spent years developing the phase splitter design. Unless it’s a lot better, of course.

I think a pallet-load of macaroons might be appropriate in this case, to go with my tea and oversized toupee.

 

What to do After You’ve Written a Few Sensible blogs.

In the interests of staying insane, or at least becoming normal, one has to get away from the ‘sensible blog’ syndrome.

So don’t expect this to help you to fix anything that a couple of aspirins won’t sort out.

So here it is…………….

                                 The Allen Invasion of the A5 Services

                                                                                          

            Wailingpolice sirens belly-ached into the night as half the motorway cop cars in the county picked out the A5 Services outside Bromfield in their strobing beams. This was all highly irregular as the belly-aches were usually inside the cafe.           

                          #

            “It still looks like a burger in a bun to me” said the prone cop sighting at it down the barrel of the .45 calibre automatic pistol. Slamming his stomach down on the tiles after a bagful of chicken nuggets had not been a wise move, the sergeant quickly realised. The officer sprawled next to him raised his Heckler and Koch and dug around in his shirt pocket distractedly.

            “The bloke on the phone said they all look like burgers; ‘there’s hundreds of ‘em’, is what he said.”

            “There would be; this is a burger bar,” said the sarge; he didn’t take his eyes off the burger, though; “but it’s dead in my sights if it tries anything funny.”

            “If that bloke was right, we’re outnumbered, sarge” said Algy, with a nervous twitch. There were, indeed, hundreds of them dotted around the floor like acne.

            “They don’t look armed, Algy.” A silence descended on the deserted restaurant, broken inconsiderately by a waitress diving for cover behind the cutlery trolley. “But would I know what sort of killer weapon a burger in a bun might carry in its, er, pocket?”

            “Don’t that one look bigger than all the rest? What do y’ think, sarge?”  

            “Of course it’s bigger. It’s a Double-Whopper-Angus-Burger. What would you think if you ordered a Double-Whopper-Angus-Burger and a sausage roll turned up?” A cleaner lady with a power floor washer walked in without looking up and plugged it into the wall.

            “Are you mad?” said the sarge.

            “I’ve been doing this job for twenty years, what do you think?” She pushed things in and pulled things out of the machine with the efficiency of a robot. Algy’s face turned puce and he looked up her rumpled stockings from the floor.

            “Look, madam, we’re on a..a…stakeout for this… er…just a minute.” Algy pulled out a crumpled reporter’s note pad triumphantly and flicked through its tacky pages; “Allen Invasion!”

            “A what?” said sarge, his eyebrows standing well clear of his forehead.

            “That’s what it says here,” said Algy.

            “You’re telling me we’ve surrounded the Blastoff Burger Bar with sixty men on the whim of a bloke who can’t spell ‘alien’?”

Just then a disembodied voice shouted something that sounded like

            “’Ten…Shun!” and the burgers that had been scattered randomly about the floor of The Blastoff Burger Bar shuffled around willy-nilly before clicking into several ranks behind the Double-Whopper-Angus-Burger. A floor-washer started up behind them and a thoroughly spooked Algy redesigned it into a cheese grater with his Heckler and Koch while surfing the soap bubble waves cascading across the tiles.

            “Help” said Algy, careering towards the ranks of the Allen Invasion Force as they opened fire with ketchup and Worcester sauce.

            “It’s ok Algy, I’ve got you covered,” shouted sarge.

            “There’s no need sarge, I’m covered already,” said Algy.

            “And you think I’m mad!” said the cleaner, formerly of the rumpled stockings and now of the floppy gumboots, as several of the Allens blasted off into the dizzy ceilings of the Blastoff Burger Bar. The sergeant battled to get a grip on his walky-talky as it danced out of his hands in the monsoon of ketchup from above and the tide of ‘Washy-Floory’ suds surging below.

            “The situation is getting messy, sir” said the sarge into the phone that was grotesquely distorting into something more Allen than the Allens.

            “Bring your leader to us!” boomed the Double-Whopper-Angus-Burger, in radical break with tradition.

            “No,” shouted Algy to the ceiling, “that’s all wrong. Your line is ‘Take me to your leader’. I saw it in ‘The Allen Goes to Hollywood’.” Just then the glimmering of dawn was obliterated by an unimaginably vast Super-Dooper-Triple-Quadruplicately-Huge-Whale-Burger that cruised, silent and deadly, over the Blastoff Burger Bar and hovered, its ketchup cannons primed like a million bristling cocktail sticks.

            “Bring us the President of the World!” said Double-Whopper from his ceiling tile.

            The sarge at last dropped his eyebrows as there was nowhere else for them to go.

            “That could be tricky” called up the sarge.

            “What! You refuse! Puny services-ling?” Double-Whopper bristled. “In that case we shall eliminate your silly civilisation.”

            “Psst. Sarge.” Algy nudged the sarge’s elbow.

            “Not now, Algy. I’ve got to think this out,” bubbled the sarge through a mouthwash of Washy-Floory suds.

            “She’ll do.” Algy pointed at the cleaner with the floppy gumboots. The sarge, aghast, looked at Algy as if he was an Allen.

            “They’ll never go for that. Just look at her.” The sarge had another look just to make sure. He shrugged. “Here she is, then;” he called up; “the President of the World.” The President of the World looked up from her ceremonial mop and bucket.

            “No!” A panicky voice rang out from the Ceremonial Ceiling Tile. “You must not invoke the gods. It will be the end of everything as we know it.”  The President of the World stubbed out a distressed fag-end and smoothed down her floral piny.

            “What you got against dogs, then?” enquired the President of the World, rolling up her sleeves and bridling her bosom.

            “PSSST!” pist Algy at the President of the World. “It said ‘gods’: not ‘dogs’.”

            “Don’t you ‘pssst’ me mate. I know my rights. That’s oppression of a Pet Owner’s Society member. I’ll set my god on you.”

            “Aaaiiiieeee! The President of the World invokes the dogs yet again.” The Double-Whopper-Angus-Burger wailed pathetically. While outside, the Super-Dooper-Quadruplicately-Huge-Whale-Burger pulsated as it sent down a majestic silver stairway through the ceiling of the Blastoff Burger Bar; along which a crowd of Allens stepped equally majestically, each Allen carrying a majestic mop and tin bucket and primrose yellow rubber gloves. They raised their majestic plungers in salute.

            Things had become very confused by this time; so they might have praised their joss-stick slungers in palute. It was hard to say.

            “No; leave all that bowing and scraping stuff out” said the President of the World, “it’s embarrassing.” The plunger-gesticulating crowd of Allens looked shamefaced, their plungers drooping to an impotent half-mast.

            “What is it that you want?” said the sarge having strung together a couple of brain cells.

            “We are collecting for ‘Uranus in Need’ and doing a bit of market research on the side” said the Double-Whopper-Angus-Burger, grandiosely.

            “It seems like a good cause, sarge” said Algy. “Nice to think somebody is collecting for mine; even though it’s not in need, so far as I know.”

            “On what terms do you do the market research, Mr., erm Double-Whopper-Angus-Burger?” enquired the sarge.

            “Oh, the usual; you get to fill out a questionnaire that takes a mere twelve hours a day for six months and get a fluffy badge for it.”

            “It’ll never catch on, here on Earth.” The sarge looked dubious.

            “According to our market research it’s what everybody does for a hobby when they’re not shouting at a computer.” The Double-Whopper-Angus Burger looked as smug as one might imagine a burger in a bun could be.

            “So,” said the sarge, tentatively exploring the limits of lunacy, “if we have a whip round and donate a few quid, you go away. Is that about it?” The burger-boss clicked its crust impatiently.

            “Don’t forget the market research!”

            “And the market research; yes.”

            “Then we must move on. One of the little moons of Mars next, I think.” If it could have smiled it probably would have. “Nice spot, Phobos.”

                            #

            To cut a short story to about the same length; i.e. tedious; in the wake of the exit of the Allen invasion force of the A5 services, (it having collected £1.52 and given out several hundred thousand market research leaflets), a month or two later followed a queue of brave politicians and journalists, both of whom were writing a blow-by-blow, fly-on-the-wall account of the event; in the same way that a duck-billed platypus did of the invasion of Greenland by aquatic camels. These intrepid seekers of truth descended on said cafe, having first taken the precaution of booking into the Dorchester for lunch.

                         #

            The leaflets from one section of the archetypal activists read:-

 

              Politician Does Something    

The Conservative party candidate for Crackbracknel, the Right Honourable Mouthmore N. Getplaces single-handedly sent people to quell an Allen invasion at the A5 services near Bromfield. He says.

 

He also says that his bravery in sending people to quash this intergalactic attack far outweighed any previous bravery as reported by any of the other parties. Whichever they were.

Sporting an open mouth and a megaphone he modestly described his battle as ‘Heroic’. Some spectators erroneously interpreted this as ‘diuretic’, which was about when it hit the fan.

The report from the police department was somewhat different.

                      #

            ‘We didn’t see hide or hair of Mr. Mouthmore N. Getplaces. We did get some fluffy badges though.’

 

                   The End (is in sight).

 

That was definitely worth tea AND a macaroon. I feel so much better. I mean, there’s nothing actually wrong with normal………..?