1-Tube Reverb addon

[Ray48]

Hi, after successfully adapting the tremolo part of the Fender Custom Vibrolux into a (German) Madamp A15Mk2 (15W push-pull) tube amp, I decided to give the 1-Tube Reverb circuit, as Tubenit used in several of his designs, a try.
And that's what I'm doing now since weeks, trying ....
I tried two reverb tanks (9AB3C1B) and several ECC83's, two different reverb transformers (125A20B - 1750A) and no result whatsoever! Bumping the tank gives a horrible thunder in the loudspeakers, what would suggest that the recovery side is working. I checked the resistors and caps.
The 1Meg reverb pot makes a cracking noise when turned about 3/4 clockwise, a newly installed potentiometer made the same noise. The circuit is actually rather simple but I can't get it to work.
I even made a whole new circuit with brand new components.
No result. I am grateful for any help or suggestions that could give me an idea about what I'm doing wrong.
You can see the attached picture of my doing so far.

[tubenit]

Without seeing the entire schematic,  I am having to do guess work ............... so I could be incorrect?

However, based on what you have shown ......................... it appears that you have a wire that bypasses the entire reverb circuit (?) and if that is the case, I am not surprised that it would not work.

I have used the one tube reverb design on quite a few amps and without exception, it has always worked whether the amp was LTPI or concertina phase invertor.


With respect, Tubenit

[sluckey]

It appears that the FX loop has your entire reverb circuit short-circuited. Surely that's not the case, but if so, just break the straight line connection between the FX send and return points.

[Ray48]

Thanks for the quick reply. I forgot to mention that the signal line to the Phase Inverter was cut as you pointed out in my drawing. So the signal goes then to the 100K resistor ( R2) and leaves the circuit on the other end of R2. I added a copy of the  original amp circuit drawing,  so you can see where the signal goes into the fx loop. At this point I connected  with R and R2 as in your circuit was shown. Hope you will excuse my bad English, but I hope you get an idea what I've been doing so far. Thanks again.
Ray48

[tubenit]

IF this is what you are saying you did ............ I have NO idea why it wouldn't work?

AND do voltages look right to you?

Having said that ........................  IF it appears to be wired correctly, I would bypass the FX loop straight into the LTPI and see
if you are getting reverb signal.

With respect, Tubenit

[Ray48]

Tubenit, thank you for the advising so far.  I even tried to cut the fx loop part and added the reverb right into the signal line to the PI. Unfortunately no result too. Will it help if I give you the drawing of the preamp? Maybe the signal could be taken from an other part of the preamp?
Greetings, Ray48

[kagliostro]

Have you try to give a look to the Vox Cambridge schematic ?

K

[Ray48]

Hello Kagliostro. The Vox Cambridge Reverb looks very interesting but isn't a 1-tube design. With 8 tubes in my amp I'm afraid the PT can't feed an extra valve. Nevertheless thanks for your reaction.
Something els is bothering me though. Measuring the voltages on  the reverb (driver) tube pins shows 283V on pin 1, 6V on pin 2 (and when turning the Dwell pot to max the voltage changes from 6V to 36V) and 2.2V on pin 3. On the recovery side of the ECC83 I measured 163V on pin 6, ZERO volts on pin 7 and 1.3V on pin 8.
Is this as it should be? I'm rather new in Tubeland but very interested to learn.
Greetings to all,
Ray48

[sluckey]

6V on pin 2 (and when turning the Dwell pot to max the voltage changes from 6V to 36V)

Pin 2 of the driver must be zero volts. It will not change when turning the dwell pot if wired IAW the schematic you posted.

[kagliostro]

The Vox Cambridge Reverb looks very interesting but isn't a 1-tube design. With 8 tubes in my amp I'm afraid the PT can't feed an extra valve.

To add a two tube reverb wasn't my intention, I only want you to give a look on the way they have implemented the insertion of the reverb, via the 3.3M resistor with the paralleled cap

the function of the resistor is to prevent the signal of the reverb to be rejected by the circuit

as you posted an incomplete schematic I haven't understand well the way you connected the reverb on the amp, may be you do exactly as in the Cambridge

I think you have already give a look to this tread http://www.el34world.com/Forum/index.php?topic=7957.0

there are also version of one tube reverb that uses pentode and triode in one bottle

K

[tubenit]

Pin 2 of the driver must be zero volts.

PLEASE follow Sluckey's direction on this & attend to this issue and report back.

Perhaps a complete schematic and photos of the build would be good in helping us help you.

With respect, Tubenit

[Ray48]

Hello Tubenit & Sluckey,
thinking about your suggestion that, according to my drawing, the circuit should work, I did cut the signal from point R (IN), left the R2 (OUT) connected as it was and made a temporary lead from R (IN) to the input jack. And voilà, there was (although not as strong as one would like to..) a nice reverb coming out of the speaker! That means, the reverb circuit is doing it's job after all.
The signal is not available right before the fx loop, but when I cut the wire between the send and return jacks, the amp is dead silent. That would mean there is a signal but it can't be used by the reverb circuit.
Once again, I'm just learning (and reading a lot...) to understand how tubes in an amp work.
I am adding the preamp drawing so one of you Gurus might enlighten me on this last part of my technical journey through tube-land.

[sluckey]

Measuring the voltages on  the reverb (driver) tube pins shows 283V on pin 1, 6V on pin 2 (and when turning the Dwell pot to max the voltage changes from 6V to 36V) and 2.2V on pin 3.

Did you fix the voltage problem on pin 2?

[tubenit]

And voilà, there was (although not as strong as one would like to..) a nice reverb coming out of the speaker! That means, the reverb circuit is doing it's job after all.

Glad to know the reverb circuit is working.

Now fix the problem that Sluckey has pointed out. Have you switched out the .001 going to the dwell pot?  That may not be the issue, but it wouldn't hurt to do so & would quickly rule another component out as problematic.

With respect, Tubenit

[Ray48]

Hello Sluckey & Tubenit,
yes, I checked the voltage on pin 2 and the voltage is now zero. Don 't know why this is so. I only changed the 100k resistor between IN and OUT to 150k and the plate resistor on pin 6 from 330k to 100k as shown in your circuit.
What do you mean by 'switched out the .001 going to the dwell pot' ? Do I have to remove this cap or change it for a new one with no result, as I did this afternoon (European time).

[tubenit]

IF the voltage on pin 2 is now zero.  Did that happen AFTER you changed out the .001 cap?  IF so, then perhaps you had a leaky cap allowing voltage thru which is why I suggested perhaps switching it out.

 

Does the amp and reverb work now? 

IF the reverb is removed does the amp work?

IF reverb and FX is bypassed allowing preamp into LTPI does it work?

With respect, Tubenit

[Ray48]

The zero voltage on pin 2 was measured with the dwell pot turned to the left. Turning it to max does the voltage increase to about 19 volts. The .001 cap was exchanged by an orange drop .001 capacitor but there was no improvement. I tried with and without a cap and still no result.
The other changes I've made were the plate resistor on pin 6 which I changed from 330k to 100k and the 100k resistor between the IN and OUT to 150k as in your circuit shown.
The amp is working OK without the reverb. Even the added  bias modulating tremolo (adapted from the Fender Custom Vibrolux Reverb) is functioning fine.
Bypassing the FX didn't do the trick either.
Your circuit is working OK if I connect the IN (R in your scheme) directly to the input jack. Not very loud because of the bypassed  preamp, but its shows the circuit is basically functioning.
I think I will let it rest for a couple of days and then see if I can give it another try.
For now I thank you all for your input and suggestions.

Ray48

[tubenit]

OK,  the preamp into LTPI is working.  

The reverb into LTPI is working.

Running the preamp into the reverb into the LTPI is not working.

So the problem (in my thinking) is that there is something wired wrong between the preamp into the reverb.

Hopefully, Sluckey will chime in and make a comment about that probably being the problem area?  

You shouldn't have voltage on the pin 2 of the reverb send. That helps pinpoint a problem area if not the problem area.

My understanding is this schematic represents what you have wired.  Is this correct?  Please answer.

With respect, Tubenit

[tubenit]

Let's work at continuing to eliminate areas and find what is working.

Would you connect a jumper wire directly from the high gain volume straight to the reverb insertion point and bypass the clean channel?

Just lift up the wire end connections from the clean channel to take them completely out of the circuit.

IF that works, then we know the problem is the other channel connection to reverb and we've narrowed it down.

With respect, Tubenit

[sluckey]

The zero voltage on pin 2 was measured with the dwell pot turned to the left. Turning it to max does the voltage increase to about 19 volts.

YOU MUST GET RID OF THAT VOLTAGE ON PIN 2. Pin 2 must be zero volts and it doesn't matter where the dwell pot is turned.

Turn the amp off. Measure resistance between pin 3 and chassis. Put meter lead directly on pin 3 of the socket. What do you get?

Turn the amp on. Measure dc voltage between pin 3 and chassis. Put meter lead directly on pin 3 of the socket. What do you get?

[Ray48]

Hello Tubenit and Sluckey ,I want you to know that, although it's 3:27 over here in the night (morning), I'm glad with this new suggestions. I was already thinking of giving up.
I will give them a try as soon as possible and then report back. This might take two or three days (the wife wants some attention too) and we're away for the weekend.
Greetings, Ray48

[PRR]

> Turning it to max does the voltage increase to about 19 volts.

If Positive 19V, the cap is leaking.

If Negative 19V, the amp is howling (since you don't mention that, it must be supersonic).