A useful Laney LC 30 mk2 blog.

I promise this will be useful. Not to Mesa, Fender, Marshall, Valco, Hiwatt, Matchless, users/ owners of course. Nor will it be much good for those needing information on house training a rhinoceros. But there will be a smattering (you didn’t know I knew that one eh?) of almost interesting information.

This (the Laney LC 30 mk2) is a noisy amp to my mind. One reason for this is that the centre tap of the heater supplies is grounded (via a 2amp fuse) to chassis. Another reason is that the pcb is grounded via the pot screws to the front panel metal work.

One thing you really don’t want in an amp is ac currents through the chassis. It introduces noise at every stage. So the best way to ground the heater CT is at a star point at the incoming earth. (At the IEC mans input in other words.) Make only one connection to each section of the chassis and lead these wires back to the same ground star point. The ground to the pots is best hard wired, again to the star point.

Sorting that out will produce a significant improvement. You can’t do much with the heater wiring. AC heater wiring is traditionally twisted together; for good reason. The twisting produces a cancelling effect of the heater current-generated hum. In this amp the wiring is not twisted anywhere in it. This amp, it seems, had an optional pcb, that converts the heater supplies to dc. In that case (if it is done well) the heaters don’t generate hum. But if it’s not a good supply design it will generate 100Hz buzz. Oh well.

The third problem that you may be able to rectify, is the fact that the design omits two control grid leak resistors on the first and third preamp valves. If you connect a 220K resistor from the centre grounded pillar of the first valve to pin 7, and repeat the procedure on the third valve, the noise levels will be attenuated by a lot of db.

I thought this was a sort of responsible blog. But I don’t get a macaroon because I didn’t get a laugh out of it. And there are few things more significant than that.

Supro Thunderbolt Reissue (well, the box is pretty close anyway.)

When is a ‘reissue’ patently not a reissue?

Taking an extreme view, anything in a Vox AC30 box, would be unlikely to be called a ‘Fender Twin reissue’. I would be, I would guess, in serious trouble if I was selling a goldfish on ebay that was actually a rhinoceros. You can’t do that sort of thing because it must contravene a trades description thing. Mustn’t it? You surely see my point, even if it does emanate from a cynical old git. That’s me, in case you were in any doubt.

And so, on to the Supro Thunderbolt ‘Reissue’. Apart from the fact that in the original had the power amp in a completely different place (bottom of the case), a quite different preamp arrangement, totally different biasing circuit…..well, the reissue is just the same.

But this was a repair job, so I should be at least a bit more useful than that. It (the reissue) has three power settings on a four pole three way rotary switch. This switch, in the one I had in, had fallen to bits. It effects the power levels in two different ways, and there are two different biasing arrangements associated with this switch. The first position, 60 watt setting switches in a 270ohm 15 watt resistor into the cathode circuit of the 6L6 output valves, so this is cathode (or automatic) bias, and much like the original circuit. In the other two positions (5watt and 1watt if I remember right) the cathode resistor is switched out and the control grids of the 6L6′s have a negative bias voltage applied, which are the other two functions of the power switch.

I think if I owned this amp, I would be wary of switching the power settings without first switching off standby. Just a thought. And now another thought. Tea and a macaroon. Nice thought.

 

Messages from the Virtual Idiot Dept

My partner has a phone. It looks like a spaceship. I have a phone that looks like a loofah. The difference between these ostensibly similar devices is that my phone does not work well in the bath either as a backscrubber or an underwater communication device; whereas I can’t make my partner’s do anything at all even standing next to EE’s gargantuan mast.

That’s because I’ve never worked out how to switch it on. By the same token I’ve never figured out how to switch it off either. She says it will make movies, take pictures, recite Shakespeare, jump up and down to the rhythm of the latest 007 Theme, act as a life raft in extreme circumstances. But I can’t ring anybody on it. Meanwhile, back at my loofah-phone, I can’t ring anybody on that either. I am told by nauseating folks at Vodaphone that it’s because I don’t put money in it. I bought it for ten quid twenty years ago; what more do they want?

I drool after those phones in the black and white ‘B’ films that people whir around with a middle finger, talk into a black stick-looking trumpet thing, and say something like “Give me Whitehall 1212, please operator”. Now, I have to key in a 54 digit, digitally secured code (that turns out not to be secure because some flea bitten company like Norton or Avast or somebody, wants to charge me a mortgage to ensure that I am secure) and after doing that I find I’ve straightened out the National Debt while waiting a day and a half in a queue for somebody from the phone company to come back off holiday to tell me how much I owe them.

So I now employ a completely revolutionary device called a ‘Hermit-o-phone’. By using this I don’t have to ring anybody at all. The first Hermit-o-phone I had I came across accidentally. I picked a banana up in Tesco and, lo and behold….it didn’t  ring! This is the phone for me, thinks I. There was also, I soon found, a bonus. I couldn’t ring anybody else, either. Another big advantage is that nobody has sent me a bill. For anything. I’ve tried this with various ‘apps’. A stick, a dog biscuit, a JCB tyre; they don’t ring you on them either.

So I’m stretched out on my blow-up mattress watching the rain outside my shed, banana on the one hand, tea and macaroon on the other.

I might have a peaceful conversation by macaroon, shortly. You’re never alone with a macaroon……..

In Praise of People we Pay Good Money to Break Things For Us

The latest in a long line of parcels that arrived as a shovelful of bits in a box that was once square-ish and had metamorphosed into some distant cousin of the arthropod species,  convinced me that sending anything to climates more distant than next door is seriously questionable. And if you got through that sentence without retching, you are made of stern stuff, and I doff my hat.

I would have to say, in the interests of fair appraisal, that my curiosity in any place more distant than arm’s length, on the Richter Scale of zero to ten, is about minus five hundred and seventy three. And you can multiply that by a lot if it’s raining.

Even taking this into consideration, I have toyed with the idea of stowing away in one of my parcels booked in for shipping (pick your own company; in my experience their records of losing/ breaking/ delivering to people I’ve never heard of, are remarkably similar), with my trusty machete and Heckler and Koch automatic. Unfortunately, I would have to be built of sheet stainless steel to survive the journey. So I shelved that plan.

So what is the most effective packing for a piece of valve equipment? Bearing in mind that there are few materials (in this Universe at any rate) that will stand being run over by a fork truck, this gets to be a problem that Einstein might balk at. So I phoned him.

“Is your name Einstein?” I asked.

“Yes” said Einstein.

“Would that be Albert Einstein?” I asked.

“It’s actually Einstein Trimblestrop; actually” said Einstein.

“I’m sure you’ll do” I said hopefully. “How would you pack a parcel to be delivered by courier to Spain? Or anywhere, really.” I asked.

“I wouldn’t send it at all” said Einstein. He thought a bit. “I did send a Victorian cast iron commode to Venezuela once. They said it looked like a toilet when it got there. I suppose that was near enough.”

“How did you pack it, Mr. Einstein?”

“I dropped it on the courier’s foot and he packed it in his plaster of Paris splint.”

So that’s solved that one. I’m now looking for my brand new packet of Macaroons shipped from Venezuela.  Easily mistaken for a box of nails when shaken.

Reconstituting smashed Venezuelan macaroons is an extended project, I can tell you. Almost as bad as repairing a new Studiomaster Powerhouse.

Now, where’s my brand new packet of tea from Venezuela………?

 

Extra terrestrial messages from an endangered species

Well, alright, it’s me really. But I am.

“What is that daft old git talking about?” You would be well within your rights to make that comment, even if it is fairly disrespectful. “So, explain yourself!” you ejaculate (?).

Alright, I will. On your own head be it. Whatever ‘It’ is.

There are few weeks go by that I don’t look inside an amp and wish for x-ray vision. Or at least an electron microscope. You can at this point visualise me (not a pretty sight) squinting at a piece of circuit board with 574 components on it. That will easily fit in my tea cup. It’s about at this point that I go to the many sites on the Wonderful Web that stack up schematics. An hour after that I’ve pulled all my hair out and am just starting on my toenails. Shortly following that, the innocent-looking pcb is in the fire bucket and I’m stomping off kettle-wards.

I started my apprenticeship in 1963. It lasted five years but I had expired well before that. (“In your dreams, mate”). It was intended to be an electrical engineering apprenticeship at the outset, but fate stepped in and after two shakes of a dead lamb’s tail it became an industrial electronics apprenticeship. This was in spite of the fact that industrial electronics and electrical engineering are as mutually compatible as bulldogs and arses.

The reason for this metamorphosis was pig ignorance by those leading the way for the electrical department, coupled with my own brand of pig ignorance. Not forgetting that electronics gear was flooding through the doors like a blizzard and there was nobody in the factory knew any more about it than how to fit a plug on the end. So I finished up at Chesterfield Technical College for seven interminable years.

So how does that equate to anything relevant to the topic? In 1963 valves (which had been around for, say, forty years plus) were being gradually supplanted by semiconductors. At the time transistors were mostly germanium and blew if placed near a stiff breeze. Whereas, valves had evolved about as far as they were going to. (The duodecatron valve was about the most complex and the mercury-arc rectifier the most powerful. In a darkened room the mercury-arc looked like something Frankenstein might have relaxed in.)

The point being (There’s a point?) that the folks who had the misfortune to be involved in electronics at the time, and also throughout the following sixty years or so, found themselves on a technological ice flow whose shape and constitution was changing almost week to week. There was no way anybody could usefully design a course to accommodate electronics servicing, because for the next decades it was changing in ways that few people could guess the direction of.

And the motivation for these technological changes was largely the pursuit of excellence. Most pursuits currently in vogue are running after greater and greater….errm…profit margins. And compared to those decades just mentioned, the changes that happen these days are painfully slow and usually restricted to being able to put more pins on a chip you can scarcely see. The ideas don’t change much at all.

I have designed a spectacularly useful electronics service course though, for current electronic repairs. I’ve called it ‘How to Plug In a New PCB”. You can do an endorsement to this which I’ve called “How to throw it Away and Buy Another One.” To keep abreast of current new ideas, we have the course entitled ‘How to Paint it a Different Colour’.

It’s very obvious that the situation will never again exist that involves living and learning through the changes that had so many ideas developing at such an extraordinary rate. The digital age has solidified like grease in a chip pan and its developments (personal opinion) are shams of convenience. But we can always expect something faster; and paint it a different colour.

There must be a kettle round here somewhere. And….a macaroon?

 

 

 

 

 

Put the ‘Cuffs on, Mate, I did it….!

This is a layman’s guide to how to get away with murder. Or close to it, anyway.

Let’s (just for a minute) consider the terrible repercussions of my stealing a box of matches. Not a robbery, you understand; just a slight misappropriation of funds. Call it creative accountancy, if you like. I did not (yer honour) waft a firearm about with abandon; neither did I threaten bodily harm, nor even the slightest suggestion of a frown did pass my forehead. I just nicked the box of matches. Displaying a certain skill, I might modestly add.

Now let’s consider the Countess of Canterbury’s diamond necklace. Using similar levels of skill and identical nonviolent techniques, I nicked it. Yer Honour. Is this a more serious felony than my nicking (in exactly the same circumstances) Cyril Crabtree’s box of matches? If the long plonker of the Law comes down harder on the diamond necklace felony than on the box of matches felony, surely the Law is more concerned with the irrecoverable nature of the knocked off goods than the crime. Will I get six months in Dartmoor for the theft of a fiver and ten years for the theft of a hundred quid? If not, why not? Which gets us to my theory that most folks on the internet should be doing time, in a big way.

“Why” quoth the affronted internet population “should’st thou level that one at us, o varlet?”

It goes like this. The real reason that the diamond thief might have got strung up in days of yore, and got a mere ducking in the village pond for half-inching Cyril’s box of (damp) matches, is relative to the ease that the contraband would be replaceable.

The most irreplaceable possession any of us has? TIME. TIME. TIME. You just cannot get it back if somebody wastes it for you.

So the next time you read some brain-dead Tweet, twitter, twatter, facebook, bong, don’t just suffer it. Send ‘em a bill. Or better still, a summons of court.

If dealing with official bodies? Send ‘em a bill. Multiply it by a few thousand.

Better still, accumulate a load of their pamphlets, circulars, polls, customer reviews, opinion polls, and post them to a deserving cause. The council, say. It doesn’t matter which one, just steal their TIME. They can’t touch you for it; sadly.

I need that cup of tea. Preferably cold , to dowse the steam blasting out of my ears.

The Unfortunate Case of the Roving Vox AC30TB

There is a short but entertaining story to this, which deals with a range of matters from lack of respect for quality to wanting to kill people from a distance to destroying irreplaceable artefacts to dealing with insurance companies to fixing the unfixable to boldly going where……you get the idea.

This little story, although sort of entertaining, was definitely not so for Marc; who shall otherwise remain anonymous. He sold his lovely old (mid sixties) Vox AC30TB to a bloke in Spain who desperately wanted to buy it. My own involvement up to that time was that I had rebuilt the output stage for him a couple of years earlier. Although you could have bought one of these new in 1965-ish for a hundred and twenty quid or so, you certainly can’t now. So, the deal was done and the lovely Vox sailed away to Spain having been packed and cased by Marc, who is the soul of conscientiousness. So it would have been very securely shipped.

After a week or so, the Spanish bloke decided that he wasn’t actually as keen on buying as he had been, and took this up with Paypal. He had a full refund, and sent the amp back. All this, although a sad indictment on honourable dealings seems (to the modern mind, at least) alright. But it didn’t stop there. The lovely Vox AC30TB came back in the in same box without any packing. I did mention ‘lack of respect for quality’ did I? It was, unsurprisingly, very much the worse for its journey, with the front baffle and casework badly damaged. It also appeared to have had less than expert hands inside it, than it deserved. It’s about here where I get involved again. Marc needed an estimate for repair for Paypal as he was making a claim for damage in transit.

The big problem with an estimate in this situation (i.e. major accidental damage) is that you need to do all the repairs to find out what it will cost. There is so much in an amp that might look (and test) alright, that actually isn’t. Not reliably so, anyway. The valves would all need to go, for a start, whether or not they tested ok.

The result of this was that the amp was a write-off, mainly because the speakers  (original Vox Blues) were damaged, and therefore it would not have been possible to bring the amp up to original spec.

What a shame. These amps should be treated with kid gloves, not hobnail boots.

A Travelogue….dedicated to Mark, the third reader of this blog

Yes; it came about after I had relieved Mark of £110 in aid of resurrecting his lovely Fender bass amp. It had blown a fair chunk of the power supplies, and fried three output valves. He admitted that he regularly read this blog. I had to believe he read it because there was no way he could hang his laptop on the nail in the bog for more useful pursuits.

So here’s one for you, Mark. Hope you and your lovely Fender are keeping well.

                       A Travelogue:-

                         How to go Somewhere Foreign.

           If you’re English, it doesn’t take you very long to catch on that there is something seriously wrong with you.

Your first problem after being born, which was finding out how to breathe, (in England, we have a Government Pamphlet for that. I know that because we have a Government Pamphlet for everything) you are then given another pamphlet that tells you who is Foreign. It’s quite a short pamphlet. It just says ‘Everybody’.

So ‘Going Somewhere Foreign’ is a really easy book to write, because if you live at ‘27, Bargery Street, Dipstick, Doobyshire,’ for instance, you know for a fact that ‘29, Bargery Street, Dipstick, Doobyshire,’ is Foreign. As are all the other numbers in Bargery Street and Everywhere Else.

So my Travelogue could be about, say; ‘32, Bargery Street’. I would then go on to discuss useful matters for the tourist of 32, Bargery Street.

The climate for instance; ‘Overbearing’ about covers it. ‘How to get around in 32, Bargery Street’; which of course contains bus timetables, when to hitch a lift on their dog, and avoiding the bedroom at certain times.

But on this occasion, just this once, you understand, I’m going for the adventurous approach. I’m going to do ‘the Solar System’.

Think big, just this once.

‘The Solar System is Very Big’. There we are, done that.

Onwards and upwards to…….A cup of tea and…..A macaroooooon!!!!!!

 

Fings Ain’t What They Used to be….An unreliable history lesson

This is a digression. It won’t help you to fix anything….except maybe make a start on the World….but then, that is too far gone to warrant the effort of throwing a spanner in it.

This little dissertation comes about from my various involvements with Carlsbro, both the real one of yesteryear and the imaginary one from China. Or wherever.

The photo is of the TC60 (actually the one after it but it looks about the same). This was Stuart Mercer’s first production (not unlike the AC30 from a distance but utterly different from every other point of view). That gentleman started the business and designed the first amps. The school group (‘band’ as it would be called now, but they were ‘groups’ then) that I accidentally started in 1959 bought a complete set of this gear from a stable block in Jenford Street, Kirkby-in-Ashfield, where he made them, in 1963. That was a couple of guitar combos, a bass top and cabinet, and a 60 watt PA system with a pair of 2×12 speaker cabinets. A total of 240 watts rms of valve power, and it was bloody LOUD. The whole lot was also £600+ and in 1963, for a group of school kids, that was a lot of dough. On the never-never (hire purchase) of course.

This was the Carlsbro bass stack. Amp missing but that looked a lot like all the others.

As with most gear of the time, schematics were not considered a black art and were easily available. In fact they were often supplied in the bottom of the cabs. Or in the case of Leak, Wharfedale and the like, they were actually stuck into the bottom chassis plate. Very sensible.

To find a current schematic for most things out of China, Indonesia, Korea, India, Botswanaland, Mars etc, you would need to get up an expeditionary force to the upper reaches of the Unpopo because that’s where they’ll turn out to be. (Under the box marked ‘Man eating crocodiles do not disturb’.)

Why is that? Too complicated? Too clever? Too self-interested? Narrrr…..none of that. They just don’t have ‘CLASS’. You can’t buy it, you can’t put a price on it, but you know when it’s there. Don’t ask me why, but a falling-to-bits AC30 or a Binson Echorec absolutely reeks CLASS. Whereas your state-of-the-art Mackie desk, or Blackstar whatsit just doesn’t.

I mean just look at this thing. TOOO COOOOL. And they sound….pheeewwww.

 

 

 

Back to the ‘history lesson’. It must be pretty obvious that I am terminally biased (?) against modernity. The price of being an old git. But I don’t care. Anybody who hates touch screens and apps and phones that take photographs and double as life rafts and do everything, but badly, can’t be all bad. You can argue with that if you like, but as I don’t care what you think, you would need to find somebody else to argue with.

Stuart Mercer started Carlsbro, as we said, in stables in Jenford Street. Presumably after the cows had been put out. He then did a lot of sweating, building prototypes. Much of this sort of grafting work is no longer done in modern design. In fact, a bloke with a degree in computer software would be better suited to designing a modern amp (even though he knew more about elephants than electronics) because this is where the ‘models’ come from. Software programs.

But Mr. Mercer had a problem. He was a qualified TV engineer, and TV engineers know little about the design of big valve power amps, but plenty about valve preamps. So he could design the tone circuits and such, but what to do about a power amp? This is where a stroke of brilliance, much representative of those days, struck him.

He bought in a Leak 50 watt rms power amp, and SCREWED IT IN THE BOTTOM OF THE CABINET!!!! From there he had to build a connecting lead from the preamp to the Leak amp and Walla !!!! A perfect solution. Doubly so, because keeping the power and preamp sections physically away from each other is a great piece of design strategy.

There might be more of this dismal rubbish; I’ve really enjoyed this tirade of insults to current thinking. I don’t really deserve a cup of tea and a macaroon, though. But what the hell….

Righty-ho clever dick….YOU design an amp……

There is the possible beginnings of a story to this one. So, as we are all ‘friends’ (in wonderful internet-speak that is. And bearing in mind you don’t know me from Adam. Or Eve for that matter) I let you in on an interesting prospect.

A gentleman I knew from a long way back called me out of the blue to ask if I would care to figure out why the amp project he had built does nothing but make nasty noises. This is regardless of what kind of nasty noises are being shoved into the front, you understand. The answer to that enquiry, although the problem I find very interesting, would usually be something like ‘GET THE HELL OUT OF HERE!!!!’ There are cans of worms and bucket loads of them, and sorting out somebody else’s design is definitely a bucket load. But Will is no idiot, a genuine bloke, and a good businessman. I don’t know about the first two but I definitely do not fall into the last category. The idea of somebody else doing business-thingies while leaving me to sort out technical issues might work out alright, thinks I.

The problem he has is with parasitic oscillation. Basically the amp is unstable (and unusable.) Not to give away too much, part of his idea was involving a class A output stage. A push-pull (class AB of some description) output stage is a naturally stable design. The reason that power amps become unstable is often that the power rail (this is a valve amp) carries some of the signal of the output back to the preamp stages and produces a positive feedback loop, not unlike acoustic feedback, which is also a positive loop. In a push -pull stage, one valve conducts through the primary winding of the centre-tapped output transformer, and the opposite valve conducts through the other half of the winding.

This means that the power rail that supplies the centre tap, has no signal content because the two halves of the transformer cancel each other out. It’s not quite like that, but close enough. Class A, for all that is trumpeted about its wonders has three serious failings. Firstly, It has to take a high dc current from the supply. It has to be biased so that the valve(s) will conduct the entire signal. Secondly, there is no cancelling effect from the dc supply rail. So the smoothing has to be very substantial, in order to kill off the inherent signal in the dc rail that is pulled by the output valves. Thirdly, the push-pull arrangement also cancels out smoothing ripple at high current drain. Again, class A relies entirely on major smoothing capacitors, iron-cored chokes etc to eliminate the 100hz ripple generated by high dc current drain.

So, although I’ve not seen the amp design yet, these are the things I’ll be looking for. Class A amp building is not an easy assignment. I’ll keep you posted on the hair loss and macaroon situation.