so I built a copy of the "Matchless DC30" amp but I used only 2 6P14P tubes (Russian EL84's) and used the output transformer form a Rigonda 102 and connected the taps for screen grids to the screen grids of the pentodes (I connected it like an ultra-linear output)
it also used 6N2P preamp tubes (Russian 12ax7's) I don't have the 2nd channel since the only 6J32P (also Russian, EF86) seems to be dead, while the heater measures 8Ohms it doesn't light up whatever I try.
anyway,
all the parts I used are pretty much scrap parts since I'm so cheap

but I used mostly ceramic or tubular caps and the only (I think) oil cap I have is the coupling cap to the PI cause I didn't have any other that was that value, but I never seen those Russian oil (I think) caps fail catastrophically i.e I only have seen a few of them be leaky in a sense that the next stage is over biased.
the only way I've seen them fail "catastrophically" is when they go pretty much open.
so that might be the case.
I'll try finding a good cap that value and change it if I find any.
I measure 293v on the output transformer for the output and 148v for the preamp tubes (but I have more dropping resistors dropping the voltage after that)
so it may be too low voltage on the preamp tubes, I'll connect it to a sooner point on the PSU.
I'll link a sound sample I recorded.
I used a small 16Ohm resistor to load the output and they used a 47nF cap (in case there's any dc) straight to my sound card.
and I have the amp cranked AND I have super-hot pickups and I am smacking the strings as hard as I can.
also at the start, I just touched the tip of the input jack thus inducing some 50Hz hum into it.
I have a 1Meg volume pot just before the PI.
untitled.mp3 (1100.32 kB - downloaded 44 times.)
EDIT: actually it's 148v for the output transformer and 293v for the preamp tubes. so I'll fix that.