Tone Stack issues TMB Modern Classic

[whboyd]

I've finally gotten my voltages all corrected and this amp works very well - EF86 channel is great and the TMB channel is good also but I can't see the treble, mid or bass controls are doing anything. I've checked & double checked all the connections and the components, and checked all the pots with a dmm but all seems to be fine.
Can someone explain the operation of the stack so I might be able to troubleshoot the issue? Thanks!

[Bieworm]

Check your wiring along with the schematic. Sounds like you bypassed the tone stack or missed a wire somewhere

[whboyd]

Thanks Bieworm, it is working beautifully now although I really don't know what I did. Just went through everything again, re-touched suspicious solder joints, re-tested components, etc.
I think I understand the basics of how it works - seems each pot just controls more signal from the cap section it works with either to the signal path or ground.

I am going to plot a frequency curve to show the effects of all the tone controls next week. I'm curious to see it to better understand the effects and maybe others will too.

Back in the day we used H.W. Sams fotofacts to help troubleshoot our amps & other electronics. They had a very great resistance chart (along with voltages & schematics) which I have done now for this amp. Your online voltage chart is a huge help so maybe the resistances will be too. I'll post it here if anyone is interested. Also shows my power supply as some will have different values.

Kind regards & thanks for all your help!

[whboyd]

Probably should mention that these resistances MUST be taken with the unit off and unplugged, and caps FULLY discharged.

[Crabman]

A possibility here is that the ground connection from your tone stack was faulty. The side effect of this would be a defeat of the tone stack. A likely candidate would be the ground connection from the mid potentiometer. This is a mod option that can be implemented in a build to remove the tone stack from the signal path.

[whboyd]

That’s interesting & entirely possible- i re-touched all the ground junctions & does work great now. Thanks for your insight!