Can anyone tell me the proper way to test a guitar amp with an oscilliscope, tone genertator,and vom meter. I know how to set the bias on a tube amplifier without a scope but I still don't quite understand what I am doing when I put a sine wave into the amplifier. I have been putting one probe on input and the other probe on output so I can compare the two waves.

Hi Mike, I can't tell you what you want to know, I guess you're looking for maximum output before clipping and symmetrical distortion. If you look down this forum to the 15th. Dec. 99 there's a posting for Bass Guitar with a lot of excellent web sites listed for guitars, you might get the information you want from there. Hope it helps, Don Black.

: Can anyone tell me the proper way to test a guitar amp with an oscilliscope, tone genertator,and vom meter. I know how to set the bias on a tube amplifier without a scope but I still don't quite understand what I am doing when I put a sine wave into the amplifier. I have been putting one probe on input and the other probe on output so I can compare the two waves.

In order to set the bias exactly, you need to attach a dummy load to the output of the amp. Set all tone controls to their mid point and feed a 1000hz signal into the amp. adjust the input signal strength and the amplifier controls to get the cleanest signal going into the output tubes. Put your scope across the dummy load to monitor the output waveform. Raise up the volume until the top of the waveform begins to clip. (becomming squared off) then back off to get the most output without clipping. If the bias is off, you will se a little hitch in the waveform at or just around the zero crossing point. Adjust the bias until the waveform is as clean as possible. (you may have to adjust the gain on the amp as you adjust the bias to keep the waveform clean.

Mike - what you're doing is correct, but I don't think
you really need to go to all that trouble to test your
amp. if you have schematics, and have already adjusted
the bias on the power tubes - then check voltages at each
stage in the curcuit. Most common problems on tube guitar
amps are either filter capacitors or coupling
caps between stages. If voltages are OK, bias voltage
is set correctly and the amp sounds good - chances
are pretty high that it's in good shape.

:ken any one giveme info a but were I be able to get
manual.