Beltone AP-22 Tone Stack Problem

[bobloblaws]

The Beltone AP-22 I'm working on had incorrect pots installed in it (500 ohm). I bought 1Meg replacement pots and decided to breadboard the control section before installing into the amp proper in case there were other issues with the amp that required troubleshooting. I have the tone stack wired up per the schematic but the treble and bass controls are doing almost nothing. The treble pot reduces the high end only marginally, it's perceptible, but only just. I expected the effect to be somewhat similar to what you would get with the tone pot on a guitar, virtual mud with the pot at 0 and gradual restoration of highs up to 10, but what I'm getting now is barely any change from 0 to 10. Instead of cutting low frequencies the bass control seems to slightly attenuate some mids and reduces the volume very slightly as well and that's it. I've played around with swapping out components to verify nothing is defective and everything seems fine in that regard. At this point I've exhausted all my ideas for troubleshooting and could use some direction/suggestions. Here is the schematic.

[Mick Bailey]

It looks an ineffective tone stack. Even without modelling it in PSpice I can see it doesn't have much tonal range. Your experience is largely shared here;

diytube.com ? View topic - Does anyone recognize this tone stack?

There are quite a few two-knob tone stacks with a much wider range, if you don't mind non-originality.

[bobloblaws]

It looks an ineffective tone stack. Even without modelling it in PSpice I can see it doesn't have much tonal range. Your experience is largely shared here;

diytube.com ? View topic - Does anyone recognize this tone stack?

There are quite a few two-knob tone stacks with a much wider range, if you don't mind non-originality.

Right, I'll have to try some other configurations.

[bobloblaws]

Put in the black/silver-face stack with 6.8K mid resistor, works great.