The Amp Garage

Replaced the 6sl7 tube socket. Not the problem.

Thanks xtian. I've any suggestions as to what resistor to add to the dropping string? I'm going to change the tube socket at the PI and change out the cap can. Maybe add a choke?

Increased the grid stoppers to 10k. No effect on the ghosting/distortion. Bad cap can?

1k5 grid stoppers might have changed the sound a little. It seems like the ghost notes might be in a bit of a higher register. When playing two notes I definitely hear a 3rd, distinct ghost note. For instance, when I play G#on the 3rd string, 11th fret and and E on the 1st string, 12th fret simultan...

Redid the preamp grounds and filtering. That made the amp quieter but didn't help the strange distortion. Moved the power tube cathode resistor off of the tube socket and onto a terminal strip so I could have more space to work with the lead dress around the power tubes. Nope. Changed out the tone c...

This morning I have replaced the 6sc7 with a 7f7, tried a 820r grid stopper on the PI input, added screen grid resistors to the to the 6l6's (not good sounding) changed the ground location of everything that I have moved back to Zottola spec, reflowed every ground connection, and cleaned out the tub...

What were the oscillations like?

Thanks guys for sticking with me through all of this. I'm puzzled as well. My only departures from the Tino Z layout originally were adding grid stoppers to the 6sc7, using a larger chassis, and using oversized iron. Maybe the larger chassis is less forgiving of the grounding scheme for some reason....

How about adding grid resistors and/or screen stoppers to the 6l6's? Is there any reason to think these could be helpful in quelling low frequency parasitics?

Not a lot of progress tonight but I did replace the PI coupling caps and change the output transformer ground from the jack to the power supply ground. No improvements.

Thanks RP. All my voltages are ok. I did adjust the dropping string to raise the screen voltages on the 6l6's but before that my voltages were within 10% of Tino Z's chart. Maybe I should try screen grid resistors? I'm using 80's vintage Russian military PIO coupling caps. I tested them for leakage ...

Thanks for the replies and suggestions guys. Keep 'em coming! Here is what I tried tonight: 1) Grounding the 27r resistor to the speaker jack. 2) Grounding the cathode of the power tubes to the same place as the can cap 3) Moving the negative feed back from the 4 ohm to the 8 ohm OT tap. 4) Changing...

Thanks Dave. Ken Fox over on the steel guitar forum pointed out that Hammonds sometimes used brown and blue leads for the opposite phase compared to Fender for the plate leads of the OT. I swapped the leads and it seemed to make the amp less brilliant (more dull) sounding. I still had the low freque...

Timely post! I too have a Bandmaster Reverb with a ticking tremolo. I'll put this info to work as soon as I get my 5b6 sorted out.

Got the scope hooked up. I have my signal generator set to 400hz and can see sine waves on all the plates of the different stages. Now, ummm, what exactly am I looking for? Can you guys help me interpret these?