Only hum from a 206A

[adcurtin]

I've got a 206A, hooked up to a 4 ohm speaker. First, I was using a direct connection to the speaker, which worked. I was using a connector before that didn't isolate the speaker ground from the chassis ground, and again it worked fine. I just switched to a different connector that will isolate the speaker ground from real ground, and all I got was hum, until fuse F2 blew, then nothing. I've tried _temporarily_ bridging the fuse, and hooked the speaker up without the new connector, and still all I get is hum. I hook a computer speaker (with its own amp) up to the preamp out, and that works fine.

Any ideas what could be causing this?

[adcurtin]

Replace the fuses, recapped the board (not the preamp yet, but that's not the problem), and replaced the output transistors (with newer equivalents), but still nothing but hum. It fried another fuse. The speaker is peaked, somehow way too much voltage is getting to it (I'm kinda surprised the speaker still works...). I think TR14 is toast, it seemed to have -22volts on all three terminals. The amp emitted some magic smoke, it burned through R34 I think (it's the 220 ohm on the bias control), which I have since replaced with a 1/2W from ratshack.

I have removed all the transistors on the main board, and plan on testing them individually, once I build a simple circuit to do so. I might just replace them all anyway, if it's cheap enough.