79 Deluxe Reverb with reverb issues

[punkykatt]

Hello all,  Did a clean & service on the amp, while checking all the resistors and E caps, I found the 680r cathode resistor for V3 12AT7 reverb driver tube burnt and cracked. I replaced that and a couple of preamp E caps that read high with the ESR meter. Everything on the amps works fine, except at times if I shut the amp off for awhile  and turn it on the reverb won`t work until I take my volt meter and start checking voltages: Start at node A nothing, node B (for screen grids) nothing, node B (for V5 tremolo junction of 100k, 10M and 220k) the reverb comes back. I tried this many times. At times the reverb will come back at nodes C and D also, but never at node A or B for the screen grids.  Has anyone ever come across this issue or have an idea what the problem may be?  any help and advise is much appreciated.  Note: all tubes have been checked and replaced. Checked all grounds.  Also when the reverb is not working there is some hash noise in the speaker.  Thank you in advance.
Punky
https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_reverb_boost_schem.pdf

[shooter]

I take my volt meter and start checking voltages: Start at node A nothing, node B (for screen grids) nothing,

by "nothing" you mean reverb? not voltage?


IF reverb; (you'll need 2 meters)
put one on V4B plate to ground when unit is off (VERIFY GOOD CONNECTIONS THAT WON'T SHORT OUT SOMETHING)
power up, verify no verb
record V4B VDC, use 2nd meter to "jump-start" reverb
record V4B VDC
did they change?


guessing there's a sketchy connection in the reverb section/power supply tap that decides to work once you give it a good path for current to flow
possibly Ecap in that circuit

[Latole]

Bad solders ?

Post good picture of the circuit

[punkykatt]

Shooter, thank you for the reply. When I connect the second meter to the plate of V4 B the reverb works every time I restart the amp.   I just discovered the eyelet board is a bit conductive, in some areas I get up to +2 vdc. Could that be part of the problem? Thanks

[shooter]

"a bit conductive"  would be 20milliVolts, HIGHLY conductive would be 2Volts.


most tubes before the PI have about 1-2volts at the cathode. 


a poor-mans "workaround";
clean out the solder at the eyelets
run wire "through" the eyelet n solder directly.

[pdf64]

What is the V3 cathode voltage when the issue is manifesting, and when it's operating correctly?

[punkykatt]

Pdf64, Voltage on the cathodes of V3 stays the same 6.4vdc with and without reverb working.

[punkykatt]

I reflowed all the eyelets on the board and doghouse board. Now the only way to turn the reverb on is to touch the voltage meter on the plate of V4 B. I subbed in a new 25uf/25v cathode bypass cap V4 B, but that didn`t help. I`m getting 211mV on the grids of V3. I`ll work on that tomorrow.

[shooter]

follow the 100K plate of V4B to eyelet
Is there a wire on the "top", resistor side that goes to D, or is the wire on "bottom" that goes to D


Either way, unsolder that eyelet so you have one end of the 100k and one end of a wire that does to D


cut a piece of shrink-wrap that will be long enough to cover the 100K's leg AND the solder connection to the wire that goes to D AND large enough diameter to fit over everything easy.  slide it down the wire out off the way


"J hook" solder 100k to wire, let cool


slide shrink-wrap over exposed metal
TEST


IF that doesn't fix, Repeat above only following the cathode side to eyelet

[punkykatt]

shooter, The 100k plate resister for V4 B is in the same eyelet as the plate resister for V4 A where they both connect to the B+ node wire that is above  board similar to the ab763 layout.


https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_reverb_ab763_layout.pdf

[pdf64]

My guess is that there's a bad connection somewhere between the amp back panel and the tank driver coil.
The signal impulse spike that results from probing V3 anode manages to break through the bad connection and make the signal path temporarily.

To test that, in the 'no reverb' fault mode, with the amp kicking out signal, is there signal at the driver IN coil? Expect a few hundred mV AC.

[tubeswell]

Use your R-meter (and test clips) to check for DC-continuity - wiggling the wires as you go

[Latole]

Yu can use any hi-fi rca cables to replace the cables from the amp to the reverb tank.
These cable work.

[punkykatt]

Thanks for the input Guy`s, I did  continuity tests the other day, all good, and I did bring some hi fi stereo cables up to Connecticut with me for the summer to sub the original cables.. My shop is down in Florida. I think there is something wonky going on with that tank even though the ohm readings  on the coils are spot on. I subbed in a reverb tank from the amp I jam with up here 8AB3C1B and there was almost twice the reverb, Plus if you shake the original tank it makes fart sounds instead of the thunder you should get. Also the reverb has been coming on every time with the subbed tank in when I re start the amp (so far). I am going to order a new tank and some plate load resisters for that circuit, it`s a bit crackly.