Laney VC30. The ‘VC’ stands for ‘Very Cwiet’.

Well, the light came on. Always a good sign. But the speaker did not speak to us.

A quick look through the rear grill told all. It was dark as the Munsters’ lounge. Or Trump’s thought processes. Not a working heater was to be found.

Inside the amp a toroidal mains transformer is mounted on the chassis, and from that, eight cables connect from the secondary of that transformer to an eight way, dual-in-line connector. The female end of this is flying and the male counterpart is fitted into the chassis. There is an interesting piece of design thinking here. Two of the cables carry the heater voltage/ current. The voltage is 6.3 volts rms. But the heater current through this connector is the total of all the heaters in the amp which is around three amps.

The connector, however, has a rating of one amp, and therefore has to carry a current that is three times its rating. Sooner or later, this is going to burn up, and it did.

The practical method of sorting this problem out is to cut all the cables on the transformer side, and solder long insulated link cables to them. The male part of the connector we prize out of the chassis. You need to make notes of what cables went to which when the connector was fitted. Then all the cables are cut to the connector. This makes it easier to desolder the cables from the pcb. Then your links from the transformer are soldered to the pcb in the order that you (hopefully) noted when you cut the cables.

This has effectively got rid of the burned connector and hard-wired the transformer wiring to the pcb.

I’ve had similar problems (for the same reasons and with similar repairs) on some Fender reissue amps. It’s a time-consuming fix, but at least the fault will not occur again.

Unless you are particularly slick with a soldering iron, this would be best left to your local tech gentleman.

Tea calleth.

 

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.

 

DBX 160xt …….under pressure….as Freddy would have had it.

The DBX 160 compressors are definitely a cut above average. They use a chip called a VCA chip. These have been used in analogue synthesisers, more or less from their inception.

You might be wondering at this point why I might want to use the word ‘inception’. Apart from it being a wondrous bullshit word, it reminds me of the Jenson Interceptor, a car with more carburettors than sense. I always thought of it as a sort family saloon AC Cobra. A great way to get rid of your ears, as it would rip them off at the first dab of the gas.

The VCA chip stands for ‘Voltage Controlled Amplifier. There were also, of the same ilk, the VCF and VCO. They were/ are respectively ;Voltage Controlled Filter’ and Voltage Controlled Oscillator’. They all worked in basically the same way. A dc voltage (the control voltage) is applied to the control pin of the chip (Before the advent of chips there were….fish. No, no! Come on, get a grip.) Let’s try that again. Before the advent of chips these devices were built up from discrete transistors. Before that, they were built from valves.

I remember a valve analogue computer at Chesterfield tech college. It had six operational amps and they shifted it from room to room on a fork truck.

The output of a VCA is proportional (I don’t know a car of that name…..wait a minute…..a pro Porche…nal. That’s relief, I thought I was turning sensible.) to the input dc control voltage. In other words, its output amplitude goes up as the dc control voltage increases. On a VCF the filter effect frequency rises or falls according to the voltage, and with the VCO the oscillator frequency rises or falls similarly.

What has any of this to do with the DBX 160xt? Well, this compressor has a VCA chip in it. The control dc voltage is sensed from the input level, and also from the setting of the compression level.

This probably won’t help to fix it, but might help a bit to understanding it.

Here’s a practical fix it bit. The DBX160 xt compressor uses a six pole push switch to bypass the compressor. If this goes bad, it won’t work, and you can’t buy one. I have heard there are plentiful stocks on Calisto, but DHL don’t ship from Mars. But you can get four pole push switches (alps switches). You can use these if you know how to a) solder and b) not panic when tracks peel off.

Take the original, bust, switch out. Tricky, but not impossible. A good desoldering device is advisable. Put the new switch in so that it occupies the 12 holes furthest from the front. Solder it in. Get a piece of heat shrink sleeving, and cut it so that the front bypass switch will push the switch operator forward. I also used a bit of the pipe from an aerosol can inside the heat shrink to make it more solid to the touch.

This will work and also switch in/ out the bypass function. What it doesn’t do is switch the led on the front which remains on. If you can live with that, you’ve fixed it.

I’m now going to phone somebody on this macaroon. It is, of course, my hermit-o-phone for the week. Last week it was a Tesco radish.

Tea…..ahhhh!

 

 

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 mains 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.

 

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.

 

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………?