Please help me!

[hypnot84]

I recently came across a Crate tv 6210 amp, which one of the power tubes wasn't working. I decided that just to be sure I would replace all old tubes with new ones, I also changed for 6l6 to el34. Now when I turn the amp off of standby it makes a squealing noise that will drop you to your knees (same sound with volume on 0 or set to 10). All the tubes are properly lit and the amp is self biasing. I'm new to the tube amp scene and I don't really know the ins and outs yet. There are 5 preamp tubes ( 4 12ax7 and 1 12ua7) I tried to look at the schematic on the crate website but the picture is all blurred. I was thinking maybe that I put the 12ua7 in the wrong place.

Thanks.

Also I forgot to mention that the amp for the most part sounded fine before I changed the tubes, all except some hum and crackling.... but nothing like the squeal that i have now.

[Andy Le Blanc]

6l6 and EL34 have different pin out, not all amps are designed or built to
accommodate both. If it squeals like that with no signal and none of the
volume up it could be either a power side issue or a wrong tube.

Can't seem to get the pdf off the crate site, got a link to the manual/schematic?

[hypnot84]

It says in the manual that the amp is built to accommodate bot 6l6 and el34 tubes. Could that go for the preamp tubes as well? When I removed the preamp tubes some of them were so worn I couldn't tell which one was the 12ax7 or the 12ua7. Is it possible that I put the 12ua7 in the wrong place and that is causing my problems?

Thanks for replying.

[David Root]

Sort of. If you put a 12AX7 in the 12AU7 slot it might do that, depends on the circuit.