So what is a ‘Phase Splitter’. Something to do with Flash Gordon, I bet.

And if you remember Flash Gordon, you must qualify for ‘Old Git’ status. Surely.

Let’s clarify this. There’s a first time for everything.

The ‘Flash Gordon’ I’m on about is not the one that Freddy Mercury waxed lyrical about. No. The Flash that I’m referring to was the one where the smoke from the rockets in outer space went upwards…..? I’m ashamed to admit that that is the only thing I can recall from my hundreds of Saturday morning visits to the local bug’s hut, the Coliseum.

Back on the topic. I think that might have been the shilling each way I bet on the dog with three legs called ‘Flash Gordon’. It lost.

A phase splitter in not a ‘phase inverter’. They are often called that these days (just as a thing you lose or break regularly is called a ‘phone’), but the phase inverter, is actually any valve that has its output from the anode. Whereas the phase splitter actually splits the phase of the input and is a specific circuit arrangement that is designed to drive two halves of a push-pull output stage. One side anode goes positive and the other side anode goes negative. Hence the phase splitting thing.

The point of this (there’s a POINT?), is that, although a lot of emphasis (and money) is put on output valve matching (and rightfully so), the phase splitter which feeds the grids of these output valves are rarely spoken about. But an internally matched ECC83 is basically a double triode valve, and if the outputs of those anodes are not well matched, the big bucks you’ve spent on some really nicely matched output valves wasn’t worth the dog I bet on called Flash Gordon.

The output valves can only reproduce whatever is going in, and if that is not symetrical, neither is your output signal.

It’s always hard to describe a sound, but the effect of this imbalance, to me anyway, is a loss of clarity and weakness of the sound. So next time you need to change output valves, get a nicely matched phase splitter to go with them.




Beware…..the Vox Concert 501 !

I do carp on a bit sometimes. You noticed? Ah, Shakespear had to write a ton of stuff to get noticed, I just have write a few sentences of drivel to get your attention.

This particular carping is regarding the afore-mentioned 1980’s Vox Concert 501. I can only think of one thing worse than not having a schematic for a piece of gear. And that is when you think you have a schematic, but, in fact, you don’t. This drawing had ‘Vox Concert 501’ written on the bottom, I had a combo in the workshop with ‘Vox Concert 501’ plastered all over it; but it may as well have been a ‘Mongoose Training for Beginners’ manual for all the use it was. Unfortunately, being a trusting sort, I thought it was the real McCoy. Until I discovered there were chips in it.

None in the schematic though. “Oh-oh” I belatedly thought. That was when I found that the third valve stage wasn’t there. At all.

Yes, I admit, I watched snails speeding past me as I wrestled with the fact that the drawing just didn’t fit what I had on the bench. From this demoralising situation, I managed to gain a positive thought. “Burn the schematic” was my best shot.

Even worse than all that, there was a switching transistor missing. This dealt with reverb footswitch operation. I hadn’t the faintest idea what it was, so I concocted a hard wired resistive network. I was convinced that this would introduce switching noise. But it didn’t!

So what the transistor (whatever it was) was for, I’ve no idea.

I most definitely get a tea-laden macaroon for that one, even if only as an anti-frustration measure.

Pi in the ski……erm….sky

In the great firmament of amp design, amp designers (Leo Fender, Jim Marshall, Dick Denny, et al) tend to be focused to the point of being obsessive. Whereas, anybody wandering his way through the vagaries of design issues who can chuck it for a couple of months at a time, (me), and then amble back into it as if nothing happened (because it didn’t), must be, at the very least, flippant.

Correct. So off we go again…….






The name ‘Pi type filter’ derives from the shape of the circuit and its resemblance to the mathematical symbol ‘Pi’.

Pi is a constant which relates the circumference of a circle to its diameter. Numerically it is 3.142 to three decimal places. However………………..

That has nothing to do with why the Pi type filter is so called. Sorry to bore you to death for no good reason. The circuit is called a ‘Pi-type filter’ because….erm… looks like it.

Below is a rather grand picture of the symbol ‘Pi’. If you compare the diagram at the top of the page to the symbol below, it becomes pretty obvious that the shape of the two capacitors and the symbol marked ‘L1 or R1’ is the same shape in essence as the Pi symbol below. If it was clever, I wouldn’t know about it, would I?



So, what is it for? What does it do?

Obviously not to make me look clever because I’ve already failed miserably on that one. If you look back at a blog of February ‘Valve rectifier and how it works’ the output of the circuit is unsmoothed dc. Which is ok for charging batteries but no good if you were charging folks to go into a show full of amps with no smoothing circuits.

Great to accompany a buzz-saw convention though. The purpose of the circuit is to convert the raw (unfiltered) dc, from the rectifier (valve or diodes, makes no difference) to constant and stable dc that the electronics it supplies can usefully work with.

Many thanks to Wikipedia for the diagram. I don’t feel too bad about nicking it because I paid ’em a fiver on their last trawl.


C1 is called the reservoir capacitor because it stores voltage. Strictly speaking it stores charge, in Joules. It charges up as the voltage increases (on the dotted line above) and discharges as the input voltage falls.

The red line is the ripple voltage, and although it is much smoother than the raw rectified dc as depicted by the dotted line, it is unlikely to be much use for supplying circuits that have to supply audio output. That ripple voltage is what happens across C1.The rest of the Pi type circuit smooths the ripple further by the action of the smoothing capacitor C2 dropping the ripple voltage across the circuit element L1 (or R1).

The physical difference between L1 and R1 is that the L signifies an inductance which is usually an iron cored choke (a coil of wire round an iron core), or a resistance. The significant difference in design is that an iron cored choke (inductance) is a lot more expensive than a resistor, and the difference in operation is that the choke is far more effective as a smoothing element in the circuit, and, unlike the resistor, doesn’t tend to drop much dc voltage across it.

So, harking back to the ‘Things in my favourite amp’ subject; which afterall is what this is all about, the smoothing / Pi type filter circuit will definitely involve the series inductance, and not the resistor. However, most amps will have a number gain stages, which are often arranged in cascade, (each stage feeding the next), and this is where we can use the dropper resistor effectively, because we often need to arrange different voltages for different stages.

There is also another issue. That of ‘decoupling’. But more of that in due course……

Tea. And I did get a chuckle or two out of this . So, also, macaroon!!


Sound City Concord….it was quite a buzzzzz.

There can’t be that many folks about who remember Sound City. And even less who want to. I hold up my hand. I actually used to sell them, when I worked in the venerable establishment of C.E.Hudson and Sons of Chesterfield (that’s Derbyshire, England.) That would have been in the ’70’s.

Some of the best, and certainly most useful, times of my life were spent during my six year sojourn there. At that time Dallas Arbiter were a big name in musical wholesale, and it was that company who was responsible for the introduction of the Sound City name to the market. The amps were designed by Dave Reeves (later of Hiwatt fame), and some big names used them; Pete Townshend being amongst them. But this all sounds too much like a boring old git carping on. Let’s just make the point that these amps were (when the design settled down) very well made and well thought of.

The one that turned up at the workshop was a Concord, which was a fifty watt 2x 12 combo, and now not far off fifty years old. It had a quite distinctive look to it, having faders for the channel volume, treble and bass controls. This one did buzzsaw impressions at a level that would have completely drowned a buzzsaw next to it. The main reservoir capacitors had dried out and that seemed to be the extent of it. After replacing the two 100uF capacitors……it stopped buzzing….and started humming. This was not quite at the level of the buzz (which had disappeared) but it wasn’t messing about, and certainly wasn’t usable.

This was a mystery. It sounded (and looked on the scope) like heater wiring hum. If the heater wiring has been moved around it can pick up. So you get a pair of longnosed pliers and (very cautiously) move the heater wiring around. The effect of that can be extreme. In this case it didn’t make any difference at all. Sometimes the heater winding on the transformer can develop shorts, so that the cancelling effect of the ac heater wiring is upset, and you get hum. One thing you can do to get round that (but not if the heater winding has an internal centre tap) is to fit a hum cancelling preset pot, which can trim the out the hum. That was not possible on this amp because it had a grounded internal centre tap on the heater winding.

It didn’t make any sense to me at all, so I shelved it, and sat in a corner for a month sucking my thumb. Then I realised that there was a distortion if a signal was put through it. Difficult to make anything of, when you have a monumental hum going on. But it was not far off half wave on the scope, which meant that half of the output stage wasn’t doing anything. THAT WAS IT!!!!!!! Eureka. Half of the phase splitter wasn’t putting a signal to one of the EL34’s.

On most phase splitters (not Ampeg) an ECC83 or ECC82 valve is arranged so that each anode (pin1 and pin6) puts out an identical (but out of phase) signal to the grids of the output valves. So that explained the distortion. But what about the hum?

There was an open circuit anode resistor, which was responsible for the lack of half the signal. But this meant that there was an open circuit at the anode of the ECC83 and that was connected via a coupling capacitor to the EL34 control grid………and picked up the hum from the heater wiring!!!!!!!   Yes!!!!!!!!

Although there were few laughs in this job, I award myself a congratulatory macaroon. And tea.




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.


And Now…A New Star in the Science Fiction Firmament. Let’s hear it for ‘Screen DeMister’.

You might have considered that most of the stuff that happens on here owes a lot to science fiction. If I was REALLY going to write science fiction; I mean, y’ know, seriously, I need a serious science fiction type name. So if you should see anything coming up written by ‘Screen DeMister’, you will know what to expect and take suitably evasive action.

Come to think of, it I could also write westerns under that pseudonym. ‘Rainstorm at the OK Corral….by Screen DeMister’. Hmmm…..wonder if Halfords might be interested….?



                                                              Charter Flight.

                                                                                                      By Screen DeMister.


            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,” 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 brush 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.


            “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


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.

In Screen DeMister’s stories ‘The End’ is usually the best bit.
































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!

Puctec ZD-987 solder/ desolder station

This is a bit off the beaten track, but might be useful. There’s a first time for everything……

I’ve used a desoldering hand pump device forever, and they work ok. For about a week. You really can’t expect too much from something that costs a couple of quid, can you? And also, if you have a lot of desoldering to do you can get a serious case of ‘pumper’s thumb (?)’ We will not go into that; but it hurts.

The big plus for this soldering/ desoldering station was that it was cheap. I may as well be brutally honest. Most of the other soldering stations (Weller, Antex, etc.) would need me to sell my grandma to drum up the cash. As I don’t have a grandma any more, my style is somewhat cramped in that investment area. It was actually surprisingly good (I’m off grandma’s now) but for one piece of missing information. It was like building a flat pack bookcase from Korea (or somewhere else foreign). On following the instructions to the letter (usually an interpretation from the early Sanskrit) it looks remarkably like a food mixer. A food mixer with a lot of screws missing.

There is a glass tube with a spring in it that should fit behind the sucky-pipe-thing. I found that a jack for a Transit van was helpful in installing this. You really have to have powerful thumbs to put this in. It is probably worth an investment in a thumb-building-up course as you have to take the tube out on a regular basis to clean out the solder waste. Except there isn’t any waste if the temperature isn’t effectively set, because it won’t desolder.

Here is the first real crunch. In the instruction sheet, it says that leaded solder melts at 180 degrees C, and leadless solder 220 degrees C. Which it does. However after some experimentation, we find that after setting the temperature to around that recommended level, we pull off the tracks quite well, but don’t actually desolder anything.

You need to desolder at around 335 degrees C. At that level it does work very well.

However, another problem (which is described in the instructions) is that at high heat levels (see workable operating temperatures) the solder tends to clog the intake pipe with a lump of lead. This lump of lead (also according to the operating instructions) you can’t get out. That’s because all the tin content of the solder alloy has been burnt off, which leaves you with a lump of lead that you can’t shift with the poking tool. Fair do’s though; Puctec do inform you of this. And also that your nice desoldering machine is unusable. Decent of them.

There is a way round this. You might have to do this a lot if you are soldering valvebase joints where there is a lot of solder to get rid of. You bring the temperature up above 400 degrees C and thump the cleaning stick in and out repeatedly. As the temperature gets up to around 380+ the solder will shift and you will have a clean tube. Sounds a bit brutal, but it works and is a lot better than chucking your nice new machine away.

Cuppa tea! And I certainly deserve a macaroon for this one.

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…



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.