new deluxe reverb style reverb oscillation

[bepone]

this also

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[imo1]

Tanks is Mod® 4AB3C1B

https://www.tubesandmore.com/products/r ... y-2-spring

Driver is 125a-20b. https://www.mojotone.com/Mojotone-Reverb-Driver-125A20B

looks like reverb is grounded.. pls check all the connections to the gnd during all connected (secondary of the reverb transformer to be grounded, reverb chassis to be grounded, reverb recovery to be grounded)

here is one shot what can cure the problem, lets start with that
IMG_1908.jpeg

Thanks for this. It’s seeming like the issue is in the recovery. I’m curious to try this and see what it does to circuit-
I can send a more detailed pic, but reverb transformer is grounded at RCA jack ground, which is chassis grounded. The reverb unit is grounded through the rca jacks, though oscillation happens with reverb into not connected. What do you mean by reverb recovery? Do you mean the next stage at the 12ax7 or the reverb output Jack? Both are properly grounded.

Question- with the grid stoppers, would you connect to grid with other side floating? I am using teflon coated wire, which isn’t as rigid as some of the older wire, where I’ve seen grid resistors connected directly to wire

[imo1]

this also
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I am following this grounding circuit. So, you would ground the 220k at that preamp ground by the input jacks?

[imo1]

Yes and one or both of those triodes could be involved. I would shorten up the grid lead on pin 2, and run it direct from the reverb return jack along the chassis surface. edit: looking again I guess maybe it isn't that long.

The grid to pin 2 is pretty short and mostly runs along bottom of chassis. I’m not the best photographer! Some of the details aren’t translating.

[martin manning]

This wire can connect like this to get some length out. Also push it down on the chassis at the socket pin. Might not fix it, but can't hurt.

[imo1]

This wire can connect like this to get some length out. Also push it down on the chassis at the socket pin. Might not fix it, but can't hurt.

Martin. Sorry. I’m not totally clear on your suggestion. Are you saying to run that grid wire along back of the chassis?Or are you saying to run the grid straighter, which would mean not along the bottom of the chassis?

I’ll reflow the solder at pin 2 to keep it closer to chassis at connection

[martin manning]

Move the connection to the other jack, and direct to the grid pin, but against the chassis.

[imo1]

Of course! Funny. Took a minute. I’ll check try that.
I am trying to figure out next steps too.

I have found when trying to diagnose this stuff in a fender circuit it can get kind of crazy. I am trying to be methodical.

What do you think about temporarily creating the plate and cathode circuit on a tag board? It’s still a little difficult because there is quite a bit going on. I am also thinking about the “y” point that goes under the board. Seems like that could somehow be crossing paths with something. I was careful with the under board routing, but can’t see it..

[martin manning]

It should work with the original layout. Here is a '65 DR. You might want to flip your socket 180° and make your wiring look more like Fender's.

[bepone]

Thanks for this. It’s seeming like the issue is in the recovery. I’m curious to try this and see what it does to circuit-
I can send a more detailed pic, but reverb transformer is grounded at RCA jack ground, which is chassis grounded. The reverb unit is grounded through the rca jacks, though oscillation happens with reverb into not connected. What do you mean by reverb recovery? Do you mean the next stage at the 12ax7 or the reverb output Jack? Both are properly grounded.

Question- with the grid stoppers, would you connect to grid with other side floating? I am using teflon coated wire, which isn’t as rigid as some of the older wire, where I’ve seen grid resistors connected directly to wire

never leave anything floating, grid stopper in series with blue wire. remove the blue wire pin 2, solder the grid stopper to the socket pin 2 , other end of grid stopper resistor solder to the blue wire...it is 30 sec job to finish maybe your problem..

[imo1]

I meant tied to a tag strip or just connected directly to the wire. I put a tag strip in because my wires are more flexible and I would worry about reliability on the road with the wire “floating”

IMG_1910.jpeg

[bepone]

ok no problem, i do "floating" with heatshrink, but all ok, now sensitive grid is isolated from reverb tank coil should be better

[imo1]

So put a grid stopper on the grid going into recovery stage as well as grounding the 220k at the cathode of that stage. Neither affected the oscillation. I am noticing an inductive hum when I put my hand close to the amp

IMG_1911.mov

[bepone]

ok, chassis is not grounded or something is not grounded or something need coax, hand on the grid wire normally will produce hum

[bepone]

if we have this situation, i would try now to separate cathodes to 12AT7 driver tube...2k2 to disconnect, jumpers, and install 2x4k7 - or for the test only one will be ok, so using only half of the 12AT7..this will tell us if the problem is driver tube, internal oscillation through the tube because of forced bias of uneaqual triodes

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