AN Wonderland reverb issue

[galtjunk]

AN Wonderland/JM 100 reverb problem

I have built the amp using Taylors' boards and chassis.
I used the layout in the JM/wonderland thread.

https://ampgarage.com/forum/viewtopic.p ... wonderland
Everything works except for the reverb.
I get no reaction to turning the send and receive pots.
If I jumper the rca plugs on the amp I get the expected response from the send
and receive controls.

I used a PT-22921 transformer and Mod 4AB3C18 reverb pan.
I connected the pan and cables to a deluxe reverb and they both work.
On the pan white is marked in and red is marked out.
I have tried the cables both ways and neither way works.

The transformer is hooked up with red going to B3a. 373v
Black to preamp ground.
Blue goes to v3 pins 1 and 6. 363v
Green goes to the center of the white rca jack.
I have a wire running from the center of the red rca jack to pin 7 of v2.
There is a 220k resistor from the center of the red rca jack to the preamp ground.

The rca jacks are isolated, the ground tabs are connected to the preamp ground.
PT and OT are Classic-Tone
All preamp tubes are 12ax7.
I have tried swapping preamp tubes.

v1-1 163v
3 1.26v
6 164v
8 1.23v
v2-1 168v
3 1.28v
6 169v
8 1.27v
v3-1 377v
3 3.9v
6 377v
8 3.9v
v4-1 158v
3 1.45v
6 158v
8 1.44v
v5-1 271v
3 55.5v
6 268v
8 55.5v



I have triple checked all of the connections on the boards, pots, switches and

sockets.

I have everything wired like the layout.

[rootz]

Your preamp voltages look a bit low to me. I’d expect between 180 and 200 Vdc on the plates of V1. That’s not the issue though,

Your cathode voltage on the driver looks low too. Iirc there should be around 7 vdc there (over the 2k2 resistor of the driver that is. I get almost 8vdc over a 3k9 cathode resistor on a single triode ecc81 driver. Thus 2mA per triode.

I had a reverb issue yesterday. The connector in the drive side of the tank didn’t make a good connection. The driver itself was fine though. I found out because I tested the driver with a signal generator and a scope. I had drive voltage on the secondary side of the reverb transformer. I suggest you test that too. Just measure if you get a substantial Ac voltage on the output of the reverb driver. Test clips to the rca connector of the cable from the driver. Also test if there is signal on the grids of the driver. If both are the case, the driver is probably fine.

You can do the same for the recovery side. Fast check: turn up the recovery and simply touch the rca jack on the cable. If you get a hum (much like when your guitar chord is plugged in the amp, but not your guitar), the recovery is probably fine.

If driver and recovery are fine, the tank is probably to blame. Since you tested the tank in another amp, there is probably a problem around either the driver or recovery stage.

Iirc the driver should put out a substantial ac swing. I believe in the order of magnitude of 20 v p-p. I’d have to check to be sure, but I’d say that anything significantly lower would suggest a problem. Of course you should turn up the send to max.

[rootz]

Misread something in your post. Your driver is an ecc83. That does work and explains the low cathode voltage. The driver should be an ecc81 though.

And I’m wrong about the preamp voltages. Should be approx 170V on the plates of V1, so you are actually pretty close.

[galtjunk]

I will try a 12at7 and see what happens.

[galtjunk]

I put in a 12at7 and the voltages came up a little.
I tried a different pan and it still didn't work.
I played it a while and the reverb came on.
I put the old pan back in and it still works.
It must have been a bad connection.

I'll keep an eye on it for a while.

Thanks for the suggestions.