PPIMV mod on SF Princeton has issue

[rockybottom16]

A friend has an old SF Princeton that's been heavily modded, including added reverb. Great sounding and LOUD little amp, but he wanted a master volume. So I recently installed a MV using the Granger Amps kit. I studied several youtube videos and I'm sure it's wired correctly. And it functions the way it should. The problem is a little hum that only occurs when the control is backed down to around 8 or 9. The pot also makes a little noise when moving between 8 and 9. When it's on 10, the noise goes away. The amp has had so much work done to it by several people, that I suspect that maybe there was some lead dress issue that the MV has "woken up". Or maybe the new pot is bad? Been scratching my head over this one. Anyone else experience this?

[Enzo]

Anyone else experience this?

Has anyone else faced your particular heavily modified amp with this specific problem? Likely not.

Mastre volume means a new pot on th panel? And wires to and from? Are they shielded wires?

[Jazz P Bass]

Not too sure what ". So I recently installed a MV using the Granger Amps kit." means.
Do you have a schematic.
I have used fellow member Bruce's PPIMV mod with great success.
(Thank you Bruce!)

[rockybottom16]

From Granger's website: "This MV is based on Ken Fisher’s Type II, with the LarMar refinement (2.2M Ohm safety resistors). It is also the most transparent when rotated fully clockwise (maxed, or “dimed”)." And yes, shielded cable used. I believe this design is the same as Triode Electronics'.

[J M Fahey]

And-WHERE-is-the-schematic?

Would you care to show the schematic referring to your question?

In your particular case, a picture showing pot and wiring would help a lot.

Thanks.

[pdf64]

Granted that though it works as intended, I don’t see what the point is of putting a master vol after a cathodyne?
Being as a cathodyne has no voltage gain and typically unpleasant overdriven characteristics.
As such, they present a totally different scenario to a typical Marshall 12AX7 LTP phase splitter, which adds maybe 39dB gain and a pleasant overdrive character.
If a master vol must be added, a type 4 between the 3rd gain stage and the cathodyne would seem to make better sense. Also would be simpler and avoid disturbing the sensitive power tube control grid circuit.