picked up what appears to be a custom made tube amp from an estate sale, tubes were in a separate box, the tube complement is (4) 6bg4, (2) 12sn7, (2) 12sl7, (1) 5u4g... unfortunately there are no markings on the amp indicating which tube is associated with which socket, I know enough to understand where the rectifier and 6bg4s fit but I'm not sure about the12sn7 and 12sl7 tubes (input stage vs. driver stage). I understand from doing some research that the plate resistance is different on these tubes. Given that, I'm assuming they are not interchangeable? or are they? if not, what is the best way to determine which goes where?
appreciate any guidance...
appreciate any guidance...
thanks for all the feedback... checked the cap values and it looks like the higher value caps are associated with the input tube socket so that should be the SL7... I'm in the process of cleaning out all the sockets and tube pins... will put it together a little later tonight with that configuration and start it up on the variac...
depends on the circuit. sl7 have a higher gain (70) compared to sn7 (20)
electrically the are interchangeable, pin for pin, but typically the sl7 are used more in the input stages and sn7 are more down the line as line stages, phase splitters and some output circuits.
for example : a two tube stereo headphone amp with a 6sl7 as its input, and a 6sn7 as its output tube.
a more complex example: 8 tube audiophile amp, (4) 6bg4, (2) 12sn7, (2) 12sl7, one half of the tubes per channel: (1) 12sl7 pre-amp , (1) 12sn7 as the phase splitter, (2) 6bg4 as outputs.
electrically the are interchangeable, pin for pin, but typically the sl7 are used more in the input stages and sn7 are more down the line as line stages, phase splitters and some output circuits.
for example : a two tube stereo headphone amp with a 6sl7 as its input, and a 6sn7 as its output tube.
a more complex example: 8 tube audiophile amp, (4) 6bg4, (2) 12sn7, (2) 12sl7, one half of the tubes per channel: (1) 12sl7 pre-amp , (1) 12sn7 as the phase splitter, (2) 6bg4 as outputs.
that appears to be the way my amp is set up...I fired it up on the variac with the sl7 as input...everything seemed fine as i got up to regular voltage levels... however, after about 10 minutes of playing one of the channels began to fade...it is now weaker than the other...I did the obvious and switched around the tubes from one channel to the other, no change... then I switched the rectifier tube with one I know is good (i don't own a tube tester yet) and still had the same weak channel... this amp was in storage for a number of years, thought I might get lucky and be able to use it without a lot of diagnostics.. well, time to flip it over and check all the caps and resistors...
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