I recently received a phone call from a gentleman called Alex who lives in Derby, UK, which is not too far from my home town of Nottingham. Alex explained that he had three tube amplifiers which needed checking out. One was a Laney 60 watt Head that someone else had looked at and apparently doctored. But........ it wasn't sounding right. The other two were........well, he didn't really know!
When Alex arrived he did indeed bring in three amps, and here's what followed:-
I did the Laney whilst he was here in the workshop. On the test gear it was indeed not doing too well. Following removal from the case it became apparent that this other engineer had put four silicone diodes, all in series, between the HT winding centre tap to ground! This, Alex had been told, was to reduce the voltage on the EL34's as it was apparently "too high".
I do agree that the voltages on some of these Laney amps is a trifle high. Nevertheless, the way that this modification had been done was a stupid idea. Yes, it does drop the voltages overall, but only when the amp is driven hard, and it does result in an immensely reduced performance. Also, on tick-over, the voltages are virtually the same, so defeating the object of trying to reduce the strain on the output bottles!!
I simply ripped out this stupid mod and put things back as they should be. I re-biased the tubes correctly and all the performance was then back to rights. Alex since tells me that it sounds great now. I’m not surprised at all!!
(As I had forgotten to take some photos of the Laney, Alex has kindly done so for my site. Thank you, Alex).
Alex had left the other two, rather strange small amps with me to check out. The first was a “B&N Crown”. I’ve never heard of or seen one of these things before. According to the circuit board it was British made, by a company called “Triumph Electronics”, down in Purley, Surrey.
This one was feeling “quite sorry for itself”. It sort of worked, but kept squealing, then going off and coming back on again! It took a little while to spot the problem, but eventually I saw a small arc coming from deep in the core of the output transformer….Ok, off it came for a rewind.
After that it now worked, but still there was some instability and buzzers. Again I soon sorted this by running a proper earth/ground from the circuit board ground to the two transformers (power and output) metal casings. These hadn’t been grounded properly, and as they are mounted on a kind of plastic/wood base, this was simply causing all the instability. A very bad design!!
I also had to re-cut and re-fit the circuit board mounting support bracket (the circuit board was “flapping around in the wind!).
I did all the obvious servicing like spraying all the potentiometers, checking the tube bases (actually changing one suspect base), replacing a couple of sad components, and finally fitting a screening can over the first stage gain ECC83. (This too was picking up stray hum etc. This whole thing really was a bad design!) And……..now it all works fine!!!
With the little 8” speaker and overdriven it sounds “wicked”, making a great studio, "crying out to be miked-up” little amp!!
The tube line-up is two ECC83’s (one for the tremolo) and one EL84. A typical 4 – 5 watts, SE (single ended), Class A with silicone rectification. A strange amp but nevertheless, cute!
And now to Alex’s third amp……Phew, what the hell is this thing!!??
On first removing the back to reveal the wiring, I just had to laugh! This is a home made amplifier, completely built on wood and fitted in an old kitchen or bedroom cabinet drawer!
The builder has left all the wires long, and joined everything up like a plate of spaghetti….Really cool!
The tubes are an ECL80 and an ECC83. The ECL80 is a triode/pentode with a common cathode. On test this “Drawer-Amp” was doing 0.8 watts (800 miliwatts......as in less than 1 watt) and it sounded awful!
I phoned Alex with the results and we decided that, although I could have sorted it out no problem, it wasn’t financially a viable repair. Alex just keeps it as a “museum piece” now…….A really funny amp!
After seeing this amp, I must tell you this little story:
Way back in 1959, at nine years old, I remember being on holiday with my mum and dad up in Peterhead, Scotland, UK. We were staying with the family of an old war colleague of my father. Andy, my father’s friend, had a radiogram in the bedroom that had been allocated to me, and this radiogram had a home-made amplifier in it. The amplifier was visible through the top as no cover had been put over it.
I can still see this amplifier in my mind’s eye. It had a 6V6GT, a 6K7G, and a big grey selenium rectifier. As my dad had dabbled with electronics for many years, we (well he) drew the circuit out for me as I was just fascinated by this thing. I’d never heard such a loud radiogram!
I can remember, on the long drive home back to Nottingham, pestering Mum and Dad to buy the two valves for me as I couldn’t wait to get back and start building the amp. We stopped at virtually every town coming home until we eventually found a small electronics workshop, down a back ally somewhere in Doncaster, where dad bought the two valves for me. I remember Mum saying that, after this, I “shut-up” for the rest of the journey home!!
A short time later, with the help of Dad, I had got together all the components for making a start, but….I needed a chassis? At this age, I was impatient and as I didn’t have a chassis I simply found a piece of half inch wood, about 15” x 6”, and started to build the unit on this!
For the ground line, I stripped off a piece of stranded cable and used drawing pins to secure it all around the side of this piece of wood. This was now my component ground return buss!
I used the adjustable power transformer from my Tri-ang model railway to light the heaters of the two valves. There was no power transformer for the HT; this was straight from the mains power with no isolation!!!! Lethal, but I didn’t care about such trivialities back then……I just wanted to get it finished and running.
This I eventually did and, with an extension speaker that Dad had built and given to me for this amp, it worked……….slightly. It felt like it was trying to work but it was very quite. I was so disappointed, as the amp up in Scotland was so loud!
I can remember when I was sorting out the parts, the input (grid 1) resistor of the 6K7 was 100k; (brown, black & yellow). I’d found one that was brown, black & red thinking that, as this was similar enough in colour, it would do!!! Little did I know at that age that red is only 1k. (I hadn’t learnt about resistor colour coding yet).
The following day, before school and after Mum and Dad had both gone to work, I had the amp on the kitchen worktop with the extension speaker and my portable record player to drive it with. I was just staring and staring at it, trying to work out what was wrong. I was so frustrated and disappointed that I decided to skive off school with the intentions of finding the problem.
At some point, my eye fell on this input resistor and I remember thinking to myself “I wonder if a yellow band in here would really make any difference as opposed to a red?” I got the scissors from the knife draw and simply cut through one of the legs. In doing so, the volume came flying out of it! It really made me jump! I can distinctly remember bursting into “tears of joy”. It sounded fantastic and I had now just learnt my first lesson on “the use of the correct resistors”!!
There were never any photos taken of this amplifier, my very first. I wish I had taken some, but having seen Alex’s “Drawer Amp” all the memories came flooding back. At least the builder of this one had the gumption to put it in a drawer, whereas mine was just simply “on a piece of wood!!”