Deluxe Reverb problem

[tyler8611]

I wonder if something is wacky; with respect to circuit common 0V, what are the actual measured Vdc at the power tubes' terminals 3, 4, 5 and 8 at idle, without a tube in V6 socket.

I will check that again. I posted those values previously when there was only a 10k tail resistor on the bias pot.

[tyler8611]

I sense a basic misunderstanding.
You are saying that you want to bias your 6V6s hotter. I.e. more bias current. At the same time you say you are trying to make the bias voltage more negative. Those are incompatible goals. The -35V shown on the schematic is just a guideline reference value. Furthermore, it was based on the original tube brands used 50 years ago with the amp operating at the line voltages of the day. You need to set the bias voltage "less negative" to achieve hotter bias or use different power tubes.

As stated above I agree that 17ma at your plate voltage may be fine. How does the amp sound at that setting? Listen with your ears not your DVM.

You're right, I gotcha. They are indeed incompatible. I was too focused on aiming for schematic range. Is there any harm in negative voltage that low?

I did play through both channels last night. The normal channel sounded good. Worked normally. Vibrato was low volume but I didn't have the reverb driver or recovery installed because I had traced the motorboating to the reverb recovery stage. So I will have to change caps there or simply touch up a solder joint, although they looked good to me. It's either the .1 coupling cap or cathode bypass. It's not the tube.

Just out of curiosity, how do you check caps for leakage in the circuit? I never got nailed that down for sure. Then again never had a leaky cap.

Oh just for laughs, last night I found out my tweed deluxe picks up bluetooth. Nice bonus feature. That'll be the next mission- finding out how to prevent that. I wonder if the same trick used to eliminate RF would work?

[Leo_Gnardo]

You're right, I gotcha. They are indeed incompatible. I was too focused on aiming for schematic range. Is there any harm in negative voltage that low?

- - - - -

Oh just for laughs, last night I found out my tweed deluxe picks up bluetooth. Nice bonus feature. That'll be the next mission- finding out how to prevent that. I wonder if the same trick used to eliminate RF would work?

With the bias voltage so low, you run the risk of trying to force the output tubes' control grids positive with a lower than normal signal level. That will result in early onset of clipping distortion. Might not be the worst thing in the world, "if it sounds good it is good" still works.

Yes, any of the usual RF suppression techniques can be used in your tweed Deluxe. Many of these have no shield on the back side of the amp, and even the ones that have metal inside the back cover, don't have that metal grounded. That's where I'd start. And these days it seems cell phone chatter finds its way into practically every amp somehow.

[tyler8611]

I wonder if something is wacky; with respect to circuit common 0V, what are the actual measured Vdc at the power tubes' terminals 3, 4, 5 and 8 at idle, without a tube in V6 socket.

Did this just now. No V6:

Pin 3: 403, 405

Pin 4: 405

Pin 5: -20.9, -21

Pin 8: 15.9 mA (64.2 mV)
. 16.2 mA (65 mV)

[tyler8611]

With the bias voltage so low, you run the risk of trying to force the output tubes' control grids positive with a lower than normal signal level. That will result in early onset of clipping distortion. Might not be the worst thing in the world, "if it sounds good it is good" still works.

Yes, any of the usual RF suppression techniques can be used in your tweed Deluxe. Many of these have no shield on the back side of the amp, and even the ones that have metal inside the back cover, don't have that metal grounded. That's where I'd start. And these days it seems cell phone chatter finds its way into practically every amp somehow.

Yeah, as long as it sounds good and is operating like it should, I'm happy. But I wanna try to identify whether there's an issue with the bias circuit that should be corrected. Maybe it's the PT 0V wiring for instance, as someone mentioned. We'll see.

The interference - I used to have an apple but switch to samsung just for the hell of it. This never happened with the apple. I was thinking of installing in the tweed deluxe a suppressor at the input, but I'd have to look up the best way to do that.

[tyler8611]

Yeah, as long as it sounds good and is operating like it should, I'm happy. But I wanna try to identify whether there's an issue with the bias circuit that should be corrected. Maybe it's the PT 0V wiring for instance, as someone mentioned. We'll see.

The interference - I used to have an apple but switch to samsung just for the hell of it. This never happened with the apple. I was thinking of installing in the tweed deluxe a suppressor at the input, but I'd have to look up the best way to do that.

I checked and it does have grounded shielding on the back.

[tyler8611]

I have an isolated problem with the V4 reverb recovery circuit causing motorboating. I substituted all the coupling caps and cathode bypass cap associated with V4. Nothing worked and I've tried four different 12AX7s- all the same result. I went in resoldered every point in the circuit.

Could it be a bad filter cap?

[Tom Phillips]

Yes. Most likely a bad fiter (decoupling) cap or bad grounding.

[tyler8611]

Yes. Most likely a bad fiter (decoupling) cap or bad grounding.

Thought so. I'll replace that particular power cap and check the grounding joints.

[Tom Phillips]

Thought so. I'll replace that particular power cap and check the grounding joints.

Don't jump straight to "replace." Troubleshoot first including connections & grounding. In this case just clip a new cap across the one in the circuit. If that makes no difference then the existing cap is not the problem.

[tyler8611]

Don't jump straight to "replace." Troubleshoot first including connections & grounding. In this case just clip a new cap across the one in the circuit. If that makes no difference then the existing cap is not the problem.

Went straight to replace and the cap ended up not being the problem. I did have to touch up the heater pins on this socket earlier. I guess I should be checking every connection.

[tyler8611]

Went though and resoldered all the associated pins. Still motorboating from the reverb recovery. I traced the problem to V4. Tries Tried multiple tubes, changed all caps, same result.

[tyler8611]

I'm not actually sure if it's motorboating per se, but its definitely a loud low rumble. Never experienced before.

[tyler8611]

I wonder now whether the problem relates to the grounding of the 2nd filter cap. I tied it along with the PI and preamp filter caps, with a wire connecting to the copper bus. Perhaps I should have grounded it with the first stage at the PT bolt with the center tap.

[Randall]

I just built a DR, I connected C and D to a copper preamp ground bus, and the first three caps to chassis next to the PT. Mine is as quiet as a mouse.