Fender Hot Rod Deluxe. You really don’t want this kind of fault.

Of any fault that can beset an amplifier, oscillation is the most damaging and also the most obscure to fault find, unless your happen to have an oscilloscope about your person. Not everybody has those. Even the symptoms are not easy to interpret.

So what is it, and why is it? The ‘what’ is easy. The amp puts out its full power, but you can’t hear it. That’s because the oscillation frequency (often) is way above any Earthlings’ hearing. I have heard that folks on Calisto whistle at frequencies in excess of a MHz, but you shouldn’t believe that because I just made it up.

The ‘why’ of this can be tricky. Without the benefit of a ‘scope you would be able to hear a fairly heavy buzz (this is the power supply putting out everything it’s got), and distortion on anything you plug into the input. That is the signal fighting with the huge oscillation signal.

But the heavy buzz could also be reservoir/ smoothing capacitor problems (which could also cause the oscillation), or possibly an output bias fault, (check bias volts, around minus 55 or so is a safe one to go for 6L6 valves), or possibly a heater/ cathode short on any valve (interaction with the volume/ tone controls will narrow it down to the first stages) before the phase-splitter.

The causes are often reservoir/ smoothing caps drying out, especially on older reissue amps. There are three 22uF and a 47uF in the Deluxe/ Deville amps, and the best plan is to change them all. Another cause is shorted windings on the output transformer. The centre tap becomes not centre because the lacquer sealing the windings has melted. You can check for that by measuring the impedance (ohms) of either output valve anode to the positive on the 47uF. They should be the same but anything up to 10% or so discrepancy should be workable.

A high voltage (1kv working) poly capacitor (say, around 0.0022 uf) across the anodes of the of the 6L6′s can work wonders in stabilising an oscillating output stage. Not a cure for all ills, though.

There we are; an almost sensible blog. I’ll need a cold shower before my macaroon.

So when do you revalve….????

As soon as somebody (usually somebody trying to sell me something) sets off with “This ECC83 (JJ…EH…Groove Tubes…Mesa…TAD….etc…etc…) has a great, really tight bottom (?), a very cool detailed mid range, a glistening array of shimmering highs”; I go into ‘dark cupboard mode’, and check the bike lock on my wallet.

Were I a NORMAL, say, twenty-year-old, (are there any of them? Were there ever any of them?), my top end range of hearing would fall just a bit short of a dog whistle. Around 20kHz. As I’m not any longer a twenty-year-old (being rather closer to a hundred than twenty) my hearing falls off at around 14kHz in the right ear and nearer 11kHz in the left. So, obviously, there is little point in sales pitching me a valve with ‘shimmering highs’ if I can’t hear them.

Extrapolating this logic, how does anybody who sells valves in Russia, or Watford, or wherever, expect to tell me (or anybody else) how we hear this, that, or the other? Bullshit and bollocks? It starts to smell like it, don’t you think?

So when might we need to swap valves? And this is not a simple question, because there is no valid answer like, say, every year or every two years. I have a 1963 Fender Tremolux amp that is completely original. Which means that the valves, and everything else in it, are 50+ years old. It still sounds great. And here is the downside of revalving an amp. The valves in your amp acquire a character (as does the rest of it; speakers, capacitors, even resistors and transformers) which becomes an irreplaceable unit. It becomes a unique piece of electronics even after a year or two, and certainly after fifty years.

The tell-tale signs that valves need replacing are not difficult to pinpoint, generally.

A loud buzz that isn’t affected by the controls……look at the power valves. The grey anodes (the metal box inside the valve) shouldn’t glow. Glow either end is ok, that’s the heater. Switch off. A valve change (all the power valves as a matched set), but don’t fit them until you’ve had the amp’s bias circuits checked. If that has a problem, your nice new valves will be destroyed, more or less straight away.

Loud hums that might (or might not) be affected by the controls, are often caused by a preamp (ECC83, say) valve fault called ‘a heater-cathode short’. It means the heater has distorted and shorted to the cathode. Change the valve. You can isolate this by removing the valves one at a time.

Whistling, ringing noises. If you tap the side of a preamp valve with pencil, a microphonic valve will ring. This can also happen with power valves. Change it (them).

Just gently moving the valve around in the valve base can often clear poor contacts on a valve base. Worth a try.

I’ve just been tapping this mug of tea with a pencil and it sounds great. The macaroon didn’t. Must be faulty.

The Kustom ’36 Coupe….In the Interests of Saving you a Lot of Money….

I can remember when Kustom first came out. I saw Buddy Rich’s bass player with one. That would have been mid-seventies, but they had been around since the early sixties. They were unusual (they looked like something out of a spaceship) and doubly so, because they were all solid state. Very few transistor amps were around at that time, nearly everything was valves, and for good reason. The transistors of the time were very dubious beasts, and we (the folks who had to fix ‘em) knew not very much about them. Whereas valve technology had been evolving for probably fifty years.

The OC and AC range of transistors were about all you could get, and they didn’t like high voltages, high currents, or heat, very much. I never did find out what they did like.

But to get back to the plot. Whatever it was.

The gentleman who owned this last one I saw (I’ve seen a few in the last year or two), had revalved it, and I think had a replacement mains transformer fitted. All because it didn’t work. The actual fault was a 5 watt dropper resistor (3.9k) that had gone open circuit. A couple of quid or so, as opposed to £100-ish for a revalve and 50+ for a transformer. And all the labour.

If you are handy in amps (you can always tell a reasonably proficient electronics feller; he has two working arms and hair that isn’t black and smoking) the easiest way to check the state of dropper resistors, is to switch on the standby and put a meter on pins one and six (the anodes) of any ECC 83 you might find.

All this is all far easier if you have a drawing. A schematic is essential if you are concerned about wasting time and money.

Un….fortunately, schematics for the ’36 Coupe are kept in a cupboard guarded by Tyrannosaurus Rex, somewhere on Mars. This is how to keep your customers happy? I don’t think so.

Tea and macaroons are now necessary. Just after I’ve jumped up and down on a picture of the MD of Kustom Amps.

The ‘Fender’ 5f1 ……a kind of Champ kit.

This was interesting, a lovely little ‘Champ-esque’ amp in a nice tweed case. Unfortunately, it’s chief claim to excellence was its chainsaw impression. There was no point in playing anything through it if it didn’t sound like a chainsaw. If I’d been a bit quicker in the brain department I could have come out with the ultimate pedal. The Chainsaw….forget the notes…chop down a tree.

On looking into the design a bit further, I had problems figuring out how even the original could have been used to record stuff like ‘Layla’ and ‘Rocky Mountain Way’. The Monty Python ’Lumberjack Song’?…..maybe. This brings us into the realms of phase cancellation. No, really.

Most valve amp heater circuits have a 6.3 volt ac supply. Which means, on the face of it, that you introduce a big 50Hz signal into the amp. And 6.3 volts rms is indeed a big signal compared with the few hundred millivolts of the input signal. As this arrangement has been working well for a long time, there must be more to it?

The problem with the 5f1 was that the heater hadn’t been grounded. In the schematic, one side of the 6.3 volt supply was grounded. Sorting that out made a big difference to the chainsaw ripping through the speaker. But I also realised that this was not going to be the ultimate in low noise amps even with the ground fitted. I explain.

If we solder a preset pot of around 100ohms, with the two ends of the track (that’s the right and left tags) to the heater terminals of, say, the preamp valve, we produce a hum balance pot. Nearly. The ground has to be lifted from the heaters and replaced onto the wiper contact of the preset. You can then trim out the heater hum by adjusting the wiper position.

How/ why does it work? Before you do this mod, you need to make sure that there is no internal ground connection to the heater winding in the mains transformer. Or your trim pot will short the heater supply to ground. Important, then.

The heater wiring is twisted together for good reason. As one side of the heater goes to a higher voltage, the other goes lower. They are opposite in phase in other words. By adjusting the wiper of our preset pot, we have effectively produced a grounded centre tap which we can adjust so that the positive phase exactly balances the negative, producing a very low resultant signal to upset the amp. Most ac heater supplies have some arrangement of this sort, often with an internal centre tap that is not adjustable. In that case you can’t fit a trim pot.

Although this made the amp useable, and reasonably quiet, it still wasn’t as quiet as it could have been. Which gets us to smoothing capacitors.

There is no doubt that a valve rectifier makes a significant, and positive contribution to the sound of an amp. But it has limitations. The main one being the surge it is able to tolerate. Within the characteristics of the valve a maximum reservoir capacitor value will be stated. In the case of the GZ34, say, it’s 50uF. It’s this capacitor that makes a big difference to the 100z component, which generates the noise in the output stage. More so in a class A amp than a push-pull design (class AB, Ab1 etc) because the class AB amp has inherent noise cancellation properties.

So this little Fender amp could have been quieter with a bigger reservoir capacitor. The original was 16uF and then a load of decoupling stuff after it for the preamps. If that was doubled, the output stage noise would be much less. But you can’t just hang an infinite capacitor on the end of your 5Y4 rectifier, because it will blow the hell out of it.

So 32uF is probably about it. And now…..away with the sensible….!!!! Ha!!!!

I only have one issue with ‘sensible’. There are millions of sensible folks and yet the world is still a miserable place. Which is why I’m very happy to write a loada rubbish. Just so long as it makes me laugh.

I am presently devising a macaroon that will stir tea. I’ve tried it on Costa Copper and McDoodle’s Doughnut Dugout, but they weren’t keen on taking the doors off to get it in.

The Hermit-o-phone is still doing well though. I didn’t get a phone call from the tax office or the gas company. Or anybody else……….

Tea and a macaroon call-eth.

 

A Very Quiet Fender Twin Reverb

I hadn’t seen John for some years, but he turned up out of the blue with the Fender described above.

Even if I looked at the amp from a distance of a lot of miles I would have known it was a ‘Reissue’. I’ve just looked up ‘Reissue’ in ‘Ballooning for Aquatics’ and it said ”Consult ’Skiing for Quadrupeds’.” Which said ‘Consult “Brain Surgery with Lump Hammers”.’ So I finished up guessing. It must mean, I thought, something old brought out again, much later. Wrong.

What it really means is ‘Nick a label off a really nice amp and make a new one that’s nothing like it.’

The overriding problem with current reissues of ‘classic’ amps, is that it’s impossible to do unless you have a raft of prospective customers with bottomless back accounts. I’ve got one of those, but only because it has a big hole in the bottom. A reissue amp has to use pcb’s. If it used solder wells, tagstrips, turret board; as the original Vox, Hiwatt, Marshalls(old ones), Fender (old ones), Selmer, Supro, Carlsbro (old ones) etc….etc…. it would be monumentally expensive (there are still a few of this breed around) because people would have to do much of the building, as opposed to computers.

This gets me (eventually) to John’s Fender Twin reissue. The almost insuperable problem of valves and pcb’s not being mutually on speaking terms rears its head. In this case the output valve bases (4x 6L6) are soldered directly through the pcb, and…… as the valves hang from the bases the heat rises and…..they get hot!!!! And if we heat up a solder joint a lot of times (it doesn’t even need to be all that hot; the melting point of tin is 232degrees c and lead is 327 c so anything over 232c burns off the tin and leaves the lead.) So it drives off the tin content of the joint and you finish up with lead. And usually cracked lead. The alloy of solder is usually 65%tin to 35% lead, and the resistivity of tin is 11,5 ohm.m whereas lead’s resistivity is 21,3 ohm.m. This means that the solder joint has twice the resistance when the tin has gone.

Another property of lead is that its flexibility is poor, and the expansion and contraction of the metal with heating produces cracks and poor contact with the joint. At its most extreme the joint can become an insulator, and your nice guitar sound has become nothing at all at the other side of this joint (which is known as a ‘dry joint’ or a ‘cracked joint’).

It’s about here when I wish I had a bit more interest in photos and things, because it would be useful. However….the fault with John’s amp was minimal, but as with a lot of pcb-based amps, not that cheap. To correctly replace a component in a pcb, you have to be able to get to the to the UNDERSIDE of the board. Pheeew! That can mean taking off wiring, marking where it came from, taking the pcb out, all to get to the track side of the pcb. If you don’t do that (it’s possible to cheat by cutting off the component and soldering to the resultant wire sticking out) you run the risk of dry joints, shorts to chassis and missing any burned tracks that might be under there. In the original version, the solder wells are visible, and the pcb dismantling zero, because there aren’t any. So the job takes five minutes, and the rest of the time can be usefully spent cleaning up and servicing.

Also, on this amp there are two wirewound dropper resistors (270 ohm if memory serves) that run hot. That’s ok, they drop the voltage from around +- 50 volts down to +- 17 volts to supply the chips and relays that the amp uses for channel switching. These two resistors are flat to the board (not ok), and so heat up the tracks underneath, and are also close to two 1000uF 35 volt capacitors which don’t like the heat. For an amp of this age (1994-ish and on) these components are ready for replacement and you need to have a good look and resolder all the joints under there.

Just as an aside, it’s interesting to note that any mortgage you might have taken out to buy a Mega-Hugely-Marvellous-Platinum Plated- Radar Controlled…..erm….guitar lead….would be a totally daft investment if you had a dry joint on the input socket.

To put this problem right would cost you 0.00000001% of your investment with Wonderful Guitar Leads Inc.

Which is but a small increase on my macaroon outlay for the decade. Tea.

 

Universal Audio S-610 preamp

This is brief set of impressions regarding a nice American made valve preamp. This one blew fuses, so not quite as nice as it should have been.

On the back of the unit there is a lot of blurb about which fuse to use for which mains voltage. What it is less than clear about is that you don’t just swap the fuse and everything is ok for the different voltage. What it says is that a 250mA fuse is for 110 volt operation and a 120mA fuse is for 240 volt operation. What is not obvious is that there has to be changes made inside the unit to effect the voltage change. You might notice that if you trawl through the user manual, but not necessarily.

There two four pin connectors mounted on the internal pcb near to the IEC input, and the free plug that fits these (looking from the back of the unit) needs to be on the left hand one for 240 volt operation or the right hand one for 110 volt operation.

Unfortunately, if you’ve bought one of these units, and it was internally set for 110volt operation, and have plugged into 240 volt mains, it will have blown the fuse in the IEC socket. You might be lucky and after changing the voltage setting to 240 it might be fine. But the electrolytics in there will have been subjected to a high over-voltage and it would be sensible to check these.

 

 

Ampeg (i.e. Loud Technologies) BA300 115

If you happened to be one of those few misguided folks who followed this blog, you may have noticed that….there hasn’t been any for quite a while. My excuse is that I have to get enough steam up to vent my spite on unsuspecting pieces of electronic equipment, and, more often than not, their manufacturers.

The Ampeg BA300, whether in the 1x 15″ or the 2x 10″ versions, seems, from the various forums I’ve read, to be leaving a trail of very disgruntled musicians in its wake.  Many of them having had these amps switch themselves off, mid-phrase. The amp then switches itself back on again after a leisurely 10 seconds or thereabouts, and then, if the volume settings remain the same, does it all again. Although the amp itself seems not to suffer any embarrassment, the same cannot be said of the bass player.

I’d like to be able to say I’d successfully repaired one of these, but the honest statement is that I’ve done no such thing. But I have spent many hours inside one, and can let you in on a few conclusions.

The first mystery is why any builder of amps can think that it’s a great idea for the amp to switch itself off if too much power is demanded of it. The traditional answer to that problem is that the amp goes into clipping distortion, the player hears that, (not pleasant) and turns it down. If the music demands a heavy distortion, the amp just doesn’t go any louder if turned beyond it’s rated power output.

This amp is a ‘clever’ amp. This means that it’s complicated, not necessarily for any good reason except for, maybe, profit boosting purposes. It is a ‘class D’ amp. The ‘D’ stands for ‘dismal’ in my book. But it actually means that it uses a modulated carrier signal (of about 450 kHz if memory serves). There are different versions of the modulated carrier technique; this one uses ‘pulse width modulation’.

They also use a switchmode power supply. It’s a lighter alternative to a traditional isolating transformer, but it has its own problems.

The power amp section is unusual, and not a bad idea. It uses a bridgemode technique, which means that the speaker is driven from both sides, instead of the usual hot drive to positive and ground to negative. The power rail voltages can be much lower than in the traditional configuration, and this results in better efficiency in  the power amp section.

There were two faults showed up on this amp. The first was easy and fairly obvious. It didn’t work. With certain faults in mosfet devices, (these are !RF640 used in a push-pull configuration) an output signal can be produced which disappears when there is no load (speaker) connected. This amp has four !RF640 mosfets. Each pair produces a push-pull output, and the two pairs are out of phase; and applied to the speaker at either side. This was the bridgemode arrangement described earlier.

These devices were replaced and…It worked!

Un…fortunately I found out that a transient (a ‘pop’ or a slap on bass) switched it off. It returned after a delay and would do the same thing again. Etc…etc…

The ‘protection’ (if that’s what it is; one could argue that it’s musical assassination) switches off the carrier signal mentioned earlier.

Clever? Yes, but not very sensible.

Time for tea.

Accutronics spring reverb

The Accutronics spring reverb has been around for a long time. They haven’t changed much, except that there are more options for the transducer specs. The idea of this little missive is to get to find out when they might be repairable. The answer to that is ‘Quite often’, and for no more money than a blob of solder. But let’s clear up what a ‘transducer’ is, for a start.

The yellow thing is a transducer.

A transducer can be many things, but basically, it’s any electronic wozzit that converts one form of energy into another. In this case, this wozzit converts movement into electrical voltage/current. Or the opposite way round, i.e. electrical current/voltage into movement.

This means that the speaker in your amp is a transducer, as is any form of microphone.

The Accutronics has two transducers, one at one end of the springs we can see in the top pic, and another (looks the same but isn’t) at the other. One is the input transducer, the amp puts out a voltage /current to this, which creates a magnetic field in a dooflicky called ‘the armature’ and this acts on two very small magnets connected to the springs. This effectively creates movement in the springline which is an analogue of the electrical impulses applied to the transducer coil. That’s basically what the transducer is; a coil. The coil at the other end (the output transducer) of the spring picks up the movement of the spring, converts it to electrical signals, and the amp’s circuitry amplifies these small signals and mixes it with the straight sound through the amp.

So the amp circuitry for the input side of the reverb is completely different to that of the output. Depending on how old (or expensive) the amp is, the drive to the input might be a chip (op-amp, and cheap), or a transistor (still cheap,) or a complementary pair of transistors (not so cheap) or a valve driving a transformer (definitely not cheap. Most early Fenders had this arrangement and the later ‘reissues etc.’ not.) It makes a big difference to the quality of the sound through the Accutronics device.

From the above we can see that, if you plug the unit into your amp the wrong way round, you are up for a disappointment, because it won’t work. The two transducers have completely different specs; the input being quite low impedance and the output very much higher. If you’re going to swap a unit in an amp, you should look on the Accutronics/Belton website, because there are a lot of variations of these things these days, whereas the early models were a spring line unit that worked, and nobody bothered too much about the numbers. Anyway, there is a code printed on these units , and you need to compare this to the various specs on their website. Not difficult, just irritating. Or maybe that’s me. Damn! I was going to do this blog without any niggly quips etc.

So what might you be able to repair in one of these?

 

The first thing to check with a multimeter set on a low ohms scale, is the readings on the phono connectors. The input should read a few tens of ohms and the output, a couple of hundred or so. If these read ok, you’re looking for a fault in the amp reverb circuitry. A check on this is easy. Turn the reverb up and put your finger on the plug of the output lead. It should buzz. If not, problems. Not easy to test whether you have a drive to the input. Grounding on the unit comes in a variety of forms. The old ones used to be grounded through the frame of the unit via the rivets that held the phono sockets in. Corrosion often messed the ground integrity up. A ground wire between the two phonos will usually sort that out. Have a good look at the wire from the phonos on the unit to the transducers. They often break because of the constant vibration of the spring unit. A break at the phono end is repairable (easy); a break at the transducer end is usually not.

Much of this can be sorted out with the unit out of the amp case.

A cup of tea. And a macaroon!

 

And Now…..KAM !!!! Another fully paid-up member of ARS

“So!” I hear you ejaculate (?); “What is this ‘ARS’ that you insist on my sensibilities?”

ARS is a fine example of the group of phrases known as ’acronyms’. It is also, by the by, a fair description of the companies who deal in ‘Anonymously Ridiculous Subterfuge’. These people’s productions are soooo….clever, that they are quite convinced that there is nobody else can repair them. This not all that surprising when you discover that the schematics are encoded in Sanskrit and buried under the Sphinx.

I have to admit that most current and recent gear blends into a sort of mess of colourless nonentity when I have to recall what they are. Or what they’re called. Or even what they do, sometimes. So I can’t really be expected to remember this KAM mixer because it also blended into the undergrowth of standardised, erm, undergrowth.

The last DJ-esque thing I looked at was a Neumark Dimension something or other power amp, and the thing I remember most about it is that it had been imported from planet Zarg; and the schematics, so far as I could work out after various expeditions up the Unpopo, were still residents of Zarg. I was bloody minded enough (on that occasion, and usually, anyway) to draw the thing out with my trusty pencil on the back of a fag packet, which enabled me to prevent the owner paying out a few hundred quid to Neumark. So it was worth the effort just for the opportunity to deal a hefty fiscal boot to the groin of another member of ARS.

Back to KAM. It’s a while ago now but the most memorable bit of it was that it looked like everything else. From my point of view that means ‘made of tin and sharp edges and most of B&Q’s stock of self tappers’. And it didn’t work. I often forget that bit because when I get something it nearly always doesn’t.

In this case the left hand output was down. After week or two’s trawling the internet, I had to admit that KAM was definitely a member of ARS. In that situation one is reduced either to:-

a) giving up; b) eating the workshop carpet; or c) having to think.

This one wasn’t that bad. If you look at the mixer from the front, on the right hand side are the two output faders. After removing a tinful of screws, the pcb is revealed, as are five SIL (single in line) chips. Four of them are situated in a square formation between the faders. The really interesting one is at the top of that pcb. This is the final amplifier before the output, and this was the one that had faulted. Get your favourite integrated circuit data book out and find the pinout arrangement for that chip. All you need then (and this test works for most op amp chips) is your multimeter, set on a volt range of say 0-25 volts or so. This is a dual chip so it has two outputs. At those two output pins you should see a zero volt reading, or at most a few millivolts. A faulty chip will often give out rail volts (that’s plus or minus 12 or 15 volts-ish). That was the case for this KAM mixer. And, once again, the customer did not spend a few hundred quid with KAM for a new mixer; but about £40 with me. I doubt, however, if he was going to heartily recommend KAM to anybody except for a good kicking.

All’s Well that Ends Well. Shakespeare said that. “And now for a cuppa and a macaroon.” I don’t think he said that.

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….