Tore-Vibe Hissing Tone Pot

[Diablo]

I've finished up building a Tore-Vibe and have been pretty pleased with it. However, playing with it a little more, I've discovered that it adds quite a bit of hiss to my amp that increases with the reverb tone control. The hiss is not effected by the other reverb controls. I can turn the mix and dwell all the way down, but the tone control still adds hiss. Anyone have any ideas how to fix this or is it just one of the "features" of the design? Thanks in advance for any debugging suggestions.

Here's a link to the schematic.
https://taweber.powweb.com/store/5h15t_schem.jpg

[loudthud]

How is the hiss when the reverb is cut off with a foot switch? You might be able to knock it down some by connecting a capacitor across R13 and/or R12. Experiment with values of 250pF to 1000pF or so. Could be a bad tube V1A or resistor R12 or R13.

[guitician]

The 2.2meg resistors used for the grids is adding hiss to this design.

[Diablo]

How is the hiss when the reverb is cut off with a foot switch? You might be able to knock it down some by connecting a capacitor across R13 and/or R12. Experiment with values of 250pF to 1000pF or so. Could be a bad tube V1A or resistor R12 or R13.

When the reverb is cut off with the foot switch, there is no hiss. Also, my original diagnosis was a little off. The dwell doesn't effect the hiss. The mix pot is the hiss master control, and the tone changes the frequency of the hiss. Perhaps hiss is the wrong description, it really just increases the noise floor. I swapped in a new 12AX7 into V1 and it made no difference at all. I remeasured R12 and R13, and they're right on the money at 220K and 100K.

[loudthud]

Some resistors are just noisey, especially carbon comps. It's interesting that the footswitch cuts the hiss off. It's either coming from the tank, the drive circuit or the resistor right at the footswitch. Disconnect the drive to the tank, if that kills it, work towards the input to see if you can find the source.

[Diablo]

Some resistors are just noisey, especially carbon comps. It's interesting that the footswitch cuts the hiss off. It's either coming from the tank, the drive circuit or the resistor right at the footswitch. Disconnect the drive to the tank, if that kills it, work towards the input to see if you can find the source.

No carbon comp resistors in this build, just metal film. I disconnected the drive to the tank, and it still behaved the same. So, I tried moving the tank away from the chassis, and as I was touching the tank and the chassis I could effect the hiss. I tried running a ground cable between the chassis and the tank and that made things worse. Then when I grabbed the output cable from the tank, the hiss got quite a bit louder. I then tried the tank in my deluxe reverb and its cables - the hiss improved quite a bit. Tried the DR cables with my old tank and it was equally quiet. So, I concluded it was just a bad shielded cable that was causing my problem.

Thanks Loudthud for the lesson in troubleshooting...