slightly off topic but relevant to this thread.
I was given a TRIX of London - possibly late 50s valve amplifier.
it was obviously designed for hifi - a three position rotary switch selects mag PU, ceramic PU, and radio. it has a volume control and a treble and bass control also.
Someone had rescued it from going to the dump - landfill etc., and sold it in a recycling centre for $5!!!!!
I removed the metal cover and there was 2 x EL84 output tubes, 2 x ECC83 preamp tubes and an EZ81 rectifier tube. I removed the bottom panel and observed a very neatly laid out wiring scheme - all wires bent at right angles and carefully laid out.
After first testing the tubes, I powered the amplifier up and observed a rather sad oscilloscope picture of the output waveform into my 8 ohm dummy load.
SO ( and here is the point of this ramble) , I measured the voltages on the 5 x TCC .05uf 350v waxed covered coupling capacitors - every one of them showed leakage - ( a capacitor is supposed to block DC voltage - 250v DC one side and 0 volts on the other side), some showed as high as 20v DC on the input grids of the output tubes, wher i was expecting to fin 0 volts (cathode biased) - no wonder the amp looked and sounded sick.
I replaced them with suitable .047uf 630v dc film types and it made a huge difference, but still there was something wrong, so i replaced the cathode bypass capacitor ( 130 ohm cathode resistor), which was a 22uf 25vdc Dubilier type, with a 220uf 63vdc electrolytic and the scope picture showed another marked improvement. I plugged my guitar in to it, and although the radio input was a little quiet, (needs another gain stage) i was blown away by the AC15 style tone I was getting from it.
MORAL of this story - if it is over 30 years old, replace ALL the coupling capacitors and electrolytics, before you shell out money on tubes - your ears will thank you for this
bajaman
ps: if anyone is interested I can post some gut shots
