ghost noting

[Down Time]

I have a fender silver face bassman that has been overhauled with filter caps, cathode bypass caps, all new resistors, new orange drop caps, new output transformer from Mercury Magnetic's, and new filter choke.
When I hit the 12th fret, the ghosting notes come through on all strings, when I am in the volume range of 6 or greater. I am repairing this for one of my customers, and is this normal at this volume, or am I chasing my tail? All the biasing is set 65 to 70% of max plate dissipation, and have checked the bias circuit, and also replaced all diodes with good quality 1N4007's.

[pdf64]

Have you replaced the bias caps? Best to go for 100uF / 100V rating.
Try measuring the ac on the B+, either side of the choke, at no signal and full signal. That will tell you how well the filtering is working.
Also try it through a different speaker cab. Peter.

[R.G.]

Try it through a different speaker first, then go to things that are harder to check and fix.

I once chased a ghost note in an amp for a few days solid and found out belatedly that one of the speakers rubbed. I can't tell you how silly that made me feel.

[Jay D]

Hello:
I have previously replaced the bias filter cap with a 100 uF, 100 VDC and still ghosts.
Thanks.

[Jay D]

Hello:
I have tried my twin reverb amp, and a peavey amp speakers, all have the same result - ghosting notes. This is a fustrating problem!

[Jay D]

Hello Peter:
A friend helped me post this thread, and I am now a member of the forum.
I have tried several speakers and several different cabinets for the Bassman, and the result has been the ghost notes.

Thanks,

Jay D.

[Down Time]

I have a fender silver face bassman that has been overhauled with filter caps, cathode bypass caps, all new resistors, new orange drop caps, new output transformer from Mercury Magnetic's, and new filter choke.
When I hit the 12th fret, the ghosting notes come through on all strings, when I am in the volume range of 6 or greater. I am repairing this for one of my customers, and is this normal at this volume, or am I chasing my tail? All the biasing is set 65 to 70% of max plate dissipation, and have checked the bias circuit, and also replaced all diodes with good quality 1N4007's.

I posted this for friend, he is now a member Jay D. I told him this a great forum full of many helpful people. I'll let him take over.

[R.G.]

If it were mine, my next step would be to measure the actual AC ripple voltage on B+, and to check the balance in both static bias current on the output tubes and the gain balance on the tubes.

I guess while I was at it, I'd use an oscilloscope to look at the bias voltage; while the cap has been replaced, it is possible that it's still got some ripple on it.

[Jay D]

Ghosting Notes

Hello:
Thank you all for your help and ideas.
I have found the problem!
Using a Fluke 189 meter on capture mode (min and max), and a digital oscilloscope with capture mode, that the AC voltage at the 0.1uF feedback capacitor was cutting out at high levels of amp volume (6 to 8 on the volume controls). What was mostly frustrating is that the capacitance tester I have used to check all capacitors, this cap check good as far as capacitance. The in-circuit testing proved to be the method for checking capacitors.

[pontiacpete]

was that .1 cap one of the new ones you put in?

[Jay D]

Yes it was, and probaly defective.
I have visited Fun with tubes website, and have a cap tester under voltage you can build. I have included the link:
A Simple Way To Test Capacitors.

Thank You,

Jay D.

[Diablo]

Maybe try resoldering the cap? Sounds like vibration at high volume is making it intermittent.

[pontiacpete]

Yes it was, and probaly defective.
I have visited Fun with tubes website, and have a cap tester under voltage you can build. I have included the link:

Thank You,

Jay D.

FWT is a great site and Max runs a very interest forum! Been reading and participating for a bit over a year there.

[Prairie Dawg]

FWT is a great site and Max runs a very interest forum! Been reading and participating for a bit over a year there.

What about testing for resistance/leakage with an insulation tester? Mine's an IRT-2 that I have used to test transformers and insulation for high resistance shorts. I think I've got some C-D cubs around here that leak like crazy.

[R.G.]

You know, one thing that doesn't get much play that will cause ghost notes is a shorted choke. That lets the ripple through to the screens where it will modulate output tube gain without changing much about the DC operations of the tube.