Problem with a tube amp

[mnordbye]

I'm repairing a friends amp at the moment (haven't started yet actually), an amp that i built for him, the HiOctane kit from AX84.com. He actually plugged on of the outputs directly to a line in on his computers sound card. Bad move, 'ey?

Anyway, i haven't tested it yet, but he says one of the gain knobs (it has dual gain knobs, one channel) is not working or working very little. Also, he thinks it sounds just like crap now.

Anyone have any good advice to were to start?

Magnus Nordbye

[ambulancevoice]

get him to pay for a new amp kit

[ItZaLLgOOd]

You need to check the output transformer.  Tube amps don't like to run without a speaker connected.  Most sites say that your not even supposed to turn them on without it being connected to a load(speaker/dummy load).  good luck

[GibsonGM]

+1 on the OT....maybe hook up an actual speaker, and take some measurements at the power tubes and post them and whatever symptoms you get on one of the amp forums at AX84 or 18Watt.  If you can isolate the problem to the output stage (and that's most likely where it is!), you can probably assume the OT didn't like the load presented by the sound card.   That would then require unsoldering the OT connections and reading the resistance of the coil at the various taps, and asking a guru if the readings indicate a blown tranny.

And of course you know, you will be VERY CAREFUL if taking any measurements inside a tube amp, where the high voltages can kill you!!  But you built it, so I'll assume you are ok with this.
Good luck!