BF Bandmaster Vol/Tone problems

Karl Oberlander · Post by **Karl Oberlander** » 17 Jan 2004 10:21 am

I've got a BF Bandmaster amp head that exhibits a strange phenomena. When I turn the volume knob to 10 then turn the treble and bass knobs toward 10 they attenuate the volume to about a half what it should be. Anyone know what is causing this? I'd like to get this amp working a bit better than this. I tried new pots but that doesn't seem to do the trick.

Thanks in advance for any helpful suggestions.

Kobe

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Gibson D-8 Console Grande - Stringmaster T-8 - Alkire EHarp D-10
Fender Super Reverb
kobe@austin.rr.com
http://home.austin.rr.com/kobeco

[This message was edited by Karl Oberlander on 17 January 2004 at 02:00 PM.]

Ken Fox · Post by **Ken Fox** » 17 Jan 2004 11:38 am

Possibly parasitic oscillation, caused by wire dress. This was problem in later Silverface amps.
You would need a signal generator, a dummy load resistor, a scope and an insulated tool (chop stick) to move the wires around while watching the scope for changes.
Do both channels have the problem?[This message was edited by Ken Fox on 17 January 2004 at 11:42 AM.]

Karl Oberlander · Post by **Karl Oberlander** » 17 Jan 2004 12:42 pm

The Normal channel does not exhibit this behaviour just the Vibro channel. I don't have that much sophisticated equipment here so I'll have to experiment. Visually the resistors and caps and wiring look good.

Kobe

------------------
Gibson D-8 Console Grande - Stringmaster T-8 - Alkire EHarp D-10
Fender Super Reverb
kobe@austin.rr.com
http://home.austin.rr.com/kobeco

Jon Light (deceased) · Post by **Jon Light (deceased)** » 17 Jan 2004 12:49 pm

Does the volume loss occur steadily as you increase the tone levels or is it a sharp drop-off when you go from 9.9 to 10?

Karl Oberlander · Post by **Karl Oberlander** » 17 Jan 2004 1:14 pm

Volume drop is a pretty steady decline.

Kobe

------------------
Gibson D-8 Console Grande - Stringmaster T-8 - Alkire EHarp D-10
Fender Super Reverb
kobe@austin.rr.com
http://home.austin.rr.com/kobeco

Jon Light (deceased) · Post by **Jon Light (deceased)** » 17 Jan 2004 1:42 pm

OK--I had a thought but you've ruled it out.

Karl Oberlander · Post by **Karl Oberlander** » 17 Jan 2004 3:59 pm

OK, I replaced the 250pF cap in the treble stack and that fixed this problem. It works as it shoud now.

Thanks for all the help guys.

Kobe

------------------
Gibson D-8 Console Grande - Stringmaster T-8 - Alkire EHarp D-10
Fender Super Reverb
kobe@austin.rr.com
http://home.austin.rr.com/kobeco