"This was the first 100 watt amplifier from 4 x EL43's that I made myself at the age of 12 or 13! This was not long before the first "branded" amp that I was to subsequently use, a Geloso, crossed my path." - John
"I remember first acquiring this amplifier at the age of 12, back in 1962. On an evening at the local Grange Community Centre, I was helping put a lot of foldable tables and chairs away in a storeroom when my eye fell on this amplifier. On asking the gentleman in charge what it was doing there, he said "Oh that. It’s been there for years and doesn’t work". I then asked him what was going to happen to it as I was interested in this sort of thing, to which he replied “If you want it take it”. This I did. I had to carry it about half a mile and at 12 years of age it was quite heavy! There was no base or a cover with the amplifier so I couldn’t lean into it in case I broke any of the valves. I was certainly glad to get it onto my bench at home!
As I seem to remember, this amp looked home made. (?) The valve line up was originally (I think), working from left to right: 1 x 6J5, 1 x 6SL7, 1 x 6J5, 1 x 6SN7, 2 x EL37, 2 x 5R4. On investigating the fault, it turned out that the mains transformer was burnt out. Shame! At this age I hadn’t yet learnt about transformer design, so there was little I could do with it.......or was there?
A few months later in 1963, when I was rummaging around in an old, burnt-out cinema with a friend of mine, about 4 miles from where we used to live here in Nottingham, we found all the audio equipment laying around. It was all charred and black with soot, but some of it looked only superficially damaged and that it might still work. My friend ended up snapping up a big Vitavox horn speaker with twin drivers on it, whilst I went for this big amplifier that was there for the picking. The amplifier itself was pretty badly burned so we left that, but somehow managed to remove the enormous mains transformer! I can still see the funny looks we were getting on the bus home with this big horn in my friend's hands, and me with this rather large chunk of iron!?
When we got back home, it was my intention to attempt to fit this transformer to the amplifier, if it worked. I was, at this point, knowledgeable enough to work out which windings on a transformer were for what. After a good clean-off of the soot and a check on the windings, I was ready to test it so..... into the mains (power socket) it went!! Reading off the voltages with my then £2.50 analogue meter, it seemed very suitable for the amp. Things were looking good. I left it on for a few hours to see if it was going to be OK after the fire damage, and it was fine. Next off came the old burnt out transformer, and I drilled new holes for this larger one that dropped through OK, but there was one big problem. As the new power transformer was considerably larger, the drop-through section with all the cables was too deep and it hit the bench before resting on the chassis!? I got around this in a very novel way by simply bending down the two end flaps of about half an inch each that ran down the sides of the chassis from front to back. This can be clearly seen in the above photo. Whilst remedying the problem, it did nevertheless leave two edges quite sharp when lifting this pretty heavy amplifier. Hey......come on..... I was 12 years old.......I didn’t care about trivial things like that back then!! Once the transformer had been fitted, the amp came to life and, after a few tired component changes, sounded pretty good. My guess is that it would have been about 70 watts from the pair of Mullard EL37’s (which I wish I still had now!!).
This was about the time when EL34’s were appearing everywhere for guitar amplifiers and to see a quad set of them in an amplifier advertisement was absolutely breathtaking at the time. It was such pictures that inspired me to re-design and re-build this amplifier to the finished article in the photo. As best as I can remember, these were the following modifications:
I needed to use the 2 x 5R4 rectifier bases for output valves so these were the first to go; replaced with 4 (2 pairs in series to handle the high inrush voltage) of the then famous metal "Top Hat" Type BY100 silicone rectifiers.
Next came a re-wire of the output tubes and the addition of 2 more. I re-designed the phase inverter stage to drive 4 bottles, along with a tube change from the 12SN7 to an ECC82. (Note the novel idea of mounting a B9A base on top of an octal plug as an adaptor!).
I think I left the first two stages as is. However I remember spending a lot of time designing my own bass/treble tone circuit around the ECC83 (- replacing the 12SL7, again on another home made adaptor).
Some of the potentiometers were a bit crackly, so a complete new set went in. Don’t ask me why the long spindles were left!? Maybe it was just trendy then or maybe I hadn’t discovered what a junior hacksaw was for at this point in my life!?
Though I have a good digital camera (pretty much a must nowadays with the internet), and have learnt how to use it reasonably well, I actually have never, throughout my life, had any interest in photography. I remember borrowing my late father’s old box camera to take this photo after he’d set it up for me. I don’t even know why I took the picture back then? Though I’m really glad that I did now.
Whilst I have good recollection of most things I have had or done in my life, I cannot remember what eventually became of this amplifier? Just memories now...........
- John.