Superstrange reverb on Normal channel problem... (BFSR)

[Victor Denance]

Hi!

For some reason, the reverb is present on my homegrown Super Reverb Normal channel (trem is on both but that's because it's a power tube bias very type trem).

The verb on the Normal channel is not as "reverby" as on the Vib channel (like half of it).

The verb on Normal channel does increase when the verb knob is turned up.

Also, there's a hint of verb on the Vib channel even when the verb knob is turned to 0.

This phenomenon does occur just the same whether the "Reverb In" plug is connected or not.

There's also a massive feedback coming from the tank (whether the "Reverb in" plug is connected or not), as soon as the verb knob is turned up past 4 (and I did my best to isolate the tank acoustically, including heavy tape, cardboard back, fabric wrapping).

Electronically, I lowered the 3.3Meg reverb paralleling resitor to 2.2Meg, but kept the 10pF cap.

The Normal channel verb problem is still here when V2 tube is pulled out (so it's not the signals mixing at the shared V1 / V2 cathode).
I messed with all the tubes and they're all fine.

The thing that bugs me the most is the problem occurs even when the "Reverb in" jack is pulled out.


Now the questions:

- Where should I look for first? (My electronics are very clean and I'd be very surprised if it'd be a lead dress issue).

- Could it be a bad tank (tank is a Belton replacement for the std Fender Accutronics.
(I'd love to cure the Verb on normal channel issue + squealing tank at the same time!)

- What is the purpose of the 10pF cap //ing the 3.3Meg verb //ing resistor?
Should I really higher the cap if I lower the resistor to 2.2Meg?

Thanks a million folks,

Victor

[txstrat]

Somehow I think it could be a grounding problem in the reverb section. Sometimes when a ground is missing in some part of the circuit the signal "searches" it's ground through other stages or circuit parts.
I'd start my search there.
The 10pF is a high pass to let high frequencies pass while the lower frequencies are damped by the 3.3meg resistor (think 2.2 meg is ok too - dampens less).

[Robert M. Martinelli]

Hi Victor, ( Hi Matt ),
This could be not the case because you stated your builds are very clean, and Matt raised a good point about the grounding issue but...I would also check the signal's path. Are you using shielded cable for all the signal paths? If not, and if the paths have not been chosen carefully, there is a chance for signal wire to pick up signals from the surroundings.

Hope this helps

Best regards

Bob

[txstrat]

Hi Bob,

since Victor stated his build very clean I didn't go in that direction.
I was also thinking of a missing mixing resistor with the signal going back to the other preamp stage.
I thought of the ground issue cause it happens also when the "reverb in" is unplugged. But now I think that leads also to your assumption.

Matt

[Chuck H]

Mediocre filter caps with longish ground leads or a questionable ground connection or scheme in this area can cause power supply coupling.

Just another idea.

Chuck