One Tube reverb - dwell control problem?

[10thTx]

I would say the voltages with/without tube are within normal limits.

Describe specifically what you hear if you bang on the reverb tank or shake the reverb tank with the amp on and reverb tube in.

Are you getting a LOUD crash or a distorted/muted tone?

IF you would double check the value of the 150k "mixing resistor" that R & R2 insertion points are connected to?

IF your mixing resistor has an open circuit, then the reverb amp (meaning send and receive triodes) would be in series instead of parallel to the signal chain. That might explain the distorted tone and the need for your odd dwell and reverb settings?

Try a value of 470k or 1M for the mixing resistor, any difference in the reverb?

[Shamadan]

Thanks
I did change mixing resistor from 100k to 330k this improved loudness of reverb and distorted sounds.
Banging reverb - Can't hear a thing
Droping amp on a floor - can hear springs a bit
Droping amp on a floor harder - springs hits cabinets bottom quite sound from speaker

I did listen to this distorted sound more and now I hear it better
Dwell doesn't change normal sound - more dwell gives more distorted sound under normal sound - I can hear 2 sounds

[10thTx]

If banging and dropping the reverb tank isn't making a LOUD crashing noise, I would suspect either a bad reverb tank as a 1st choice OR something is improperly wired.

The return of the reverb "amp" (meaning the entire reverb circuit) either isn't working (possibly due to not being wired correctly ......... OR the reverb tank/pan is defective.

With any amp I've installed a one tube reverb in, banging the reverb tank and/or "dropping" the amp created an obnoxiously LOUD noise.

Take an amp like the Fender Princeton reverb and hit the reverb pan with the amp and reverb turned on, it will make an incredibly LOUD sound.

with respect, 10thtx

[Shamadan]

Thanks 10thTx I will chack it. I will look under the turret board tommorow if all fine new tank it is. I took the tank out hiting strings make a small sound. Hopfully I did some stupid mistake - if its tank i would be MAD

I will check recovery reverb triode with my guitar - will see if it works

[jjman]

The 2meg pot from the reverb output is not wired correctly in the scheme. Not sure if that was mentioned.

[10thTx]

What are you seeing that is not correct with reverb pot? The 330k resistor connects with pot & the tiny gap in the drawing is just a cut and paste issue. Is that what you're referring to?

[Shamadan]

Did some more tests.
I pluge guitar to recovery- can play but not very loud using 12u7. Change to 12x7 and its louder lets say bedroom volume.
I connected tank to make some crashing tests with 12ax7 it's louder but nothing disturbing. I play with dwell a bit and than it happened. Oscillation with dwell past 7 very tiny but could cause distorted sounds. I thought that my lead dress was good but apparently will have to work on that. Reverb transformer wire was to close to unshielded signal wire.
I am not 100% sure but I don't think that hitting tank in this circuit would make huge noise - there is only one +gain stage before power tubes. With Princeton Reverb 4 +gain stages. But thats my first reverb so correct me if I'm wrong.

[Structo]

In my limited experience with reverb tanks, any time I would move the amp or tap on the tank, it would make pretty loud crashing sounds.

I am not saying your tank is bad, double check wiring to be sure it isn't a mistake.

[Shamadan]

HI. I was trying to solve this problem for a while now. (fixed small oscillation but not main issue) I disconnected few wires and what is left on schematic still causing problems. If I remove ground from reverb driver cathode resistor - dwell doesn't effect sound. I replaced all components in this section. I don't know how can this cause any problems but it somehow does. More dwell more distorted sounds. I have put 100k grid resistor on reverb tube but it didn't change much. If You have any ideas how to fix it I will give it a shoot.

[10thTx]

New reverb tank? Use 1M dwell resistor instead of a pot?

[Shamadan]

Old reverb tank.
I tried 1M resistor and no change. I disconnected tank, reverb transformer, B+ as on schematic and still problem remains - I think that this circuit is somehow effecting cathodyne PI but don't know how. (and if it can be fixed) I did few tests last week. And when I disconnected reverb transformer - dwell was changing voltege across cathode resistor (from few mV to 0 - if i remember correctly)

[martin manning]

What happens if you disconnect the wiper of the dwell pot? If the problem goes away, and all you have connected is what's shown in the schematic, it must be a problem with the reverb driver tube (take it out and see if the problem persists), or the socket, or some wiring error like a short between pins.

[Shamadan]

I changed all ( wires, resistors, pots, capacitors, tubes, grounding, B voltage) that could cause this problem except socket. Will have to order some more and give it a try. Putting grid resistor like 200k reduced distortion but weaker reverb.
With lower B+ like 80V (few days ago I install a switch with two B+ options 380V and 80V) those distortion are gone but reverb is very week so it can be that I can't hear it well.


To be honest I love this amp and want to make it perfect. So one last obstacle remains. Hopfully it's just a socket - but can't see anything wrong with it?I would order tank but in my country there is only one shop that have them and no point to order from them if they have faulty batch. So would need to order from ebay but 60$ hurts. Thanks.


Disconnecting dwell wiper - No distortion.

[10thTx]

it must be a problem with the reverb driver tube (take it out and see if the problem persists), or the socket, or some wiring error like a short between pins.

Given what you've tried, I agree with the above.

With respect, 10thtx

[Shamadan]

Ok will check it. I was expecting a socket but I have beltons so i rule that out. Once during tests something strange happened for few minutes. I was taping on heaters wire and could hear this taping in reverb sound from speaker-only heater wires next to reverb tube. Than small crack sound and it didn't happen again but It may point to socket or wiring.
It was strange but I said hey - wired staff can happen once. So I forget about it, but now I think It could matter. Thanks for Ideas. Will report if any progress.