1978 Fender Super Reverb UL -- WEAK REVERB HELP!

[cluster]

Got a 78 Super Reverb with the UL OT and MV. Been trying to clean it up and get it running again. Completely disconnected the MV/Push-Pull since I hate those MV-Boosts on the late Fenders. My issue now is weak reverb. Tank seems ok. I smack the tank and I get that famous reverb rattle coming through. I swapped out both the driver and recovery tube -> no change. I swapped the reverb tank -> no change. Cleaned and tested the cables -> no change. I do get the typical increased signal noise when I turn up the reverb pot. Signal noise goes away when I switch reverb off on the foot switch. So everything seems to work, but still very weak reverb. Pulled the reverb cables and tested the reverb transformer red-blue = 1.95kohms, black/green=1ohm but red to green = 30kohms but dropping resistance. Not constant. Does this mean the reverb transformer is dead?? Thoughts.

Thanks so much.

[Chuck H]

There's some tricky stuff with the switching for the master volume on that amp that affects the reverb circuit. If you didn't remove the master volume and it's associated switch functions correctly this may be having an affect on the reverb signal.

Since your recovery stage seems to be behaving as normal (other than hum ) look to the input stage. Notice in the schematic that there is a 1k shunt to ground at the input when the MV switch is in one position. Considering the reverb transformer and tank impedance I wouldn't expect that to make much difference at all, but if anything is cattywhompus about the removal process there may be different circumstances. And, of course, the plate voltage and cathode current of the reverb driver tube and the signal going into it could be tested.

[Helmholtz]

Got a 78 Super Reverb with the UL OT and MV. Been trying to clean it up and get it running again. Completely disconnected the MV/Push-Pull since I hate those MV-Boosts on the late Fenders. My issue now is weak reverb. Tank seems ok. I smack the tank and I get that famous reverb rattle coming through. I swapped out both the driver and recovery tube -> no change. I swapped the reverb tank -> no change. Cleaned and tested the cables -> no change. I do get the typical increased signal noise when I turn up the reverb pot. Signal noise goes away when I switch reverb off on the foot switch. So everything seems to work, but still very weak reverb. Pulled the reverb cables and tested the reverb transformer red-blue = 1.95kohms, black/green=1ohm but red to green = 30kohms but dropping resistance. Not constant. Does this mean the reverb transformer is dead?? Thoughts.

Thanks so much.

The reverb transformer (022921) in my '66 Super Reverb measures:

Primary (blue-red) : 1.85k
Secondary (black-green): 0.85 Ohm

Any measurements between primary and secondary leads should read open. But make sure you are not touching both contacts with your fingers while measuring. Otherwise you will read your body resistance.

[cluster]

Thanks for that. I think your right. I completely disconnected the MV Push Pull pot and I might have messed with the reverb circuit by accident. Here is a gut shot with outlines of the points I cut. The yellow was from the MV volume. And the green is from the push-pull. I remember the push pull connecting to the green wire from the reverb 2nd transformer. I might have disconnected a round wire or something. I did jumper where the MV pot was on the board (yellow wire). Anyways, any recommendations on what I can jumper or wire up to see if I could get the reverb working again. Thx

There's some tricky stuff with the switching for the master volume on that amp that affects the reverb circuit. If you didn't remove the master volume and it's associated switch functions correctly this may be having an affect on the reverb signal.

Since your recovery stage seems to be behaving as normal (other than hum ) look to the input stage. Notice in the schematic that there is a 1k shunt to ground at the input when the MV switch is in one position. Considering the reverb transformer and tank impedance I wouldn't expect that to make much difference at all, but if anything is cattywhompus about the removal process there may be different circumstances. And, of course, the plate voltage and cathode current of the reverb driver tube and the signal going into it could be tested.

[cluster]

took some voltages:

Reverb transformer primary:
blue = 372 DCV
red = 396

Reverb transformer secondary:
black=green= 0 DCV (does this mean the transformer is dead)

Reverb Driver Tube V3a:
Plate=378, Grid=0.235, Cathode=7.77

Reverb Driver tube V3b:
Plate=377, Grid=0.383, Cathode = 7.91

Reverb Recovery tube V4a:
Plate=245, Grid=0 (bad sign??) , Cathode=1.8

Reverb Recovery Tube V4b:
Plate=240, Grid=.06 Cathode=1.8

[cluster]

So I opened up the cap tray and found this:

I wonder if this bad cap could be part of the problem??

[nevetslab]

Old date codes....7840 = 1978 40th week; 7906 = 1979 6th week. You're approaching 40 yr old birthday on those caps, so while this wouldn't be the problem of your weak reverb, it does show you've got some caps, one which is definitely leaking poop out the vent hole. Time to replace them.

[cluster]

Old date codes....7840 = 1978 40th week; 7906 = 1979 6th week. You're approaching 40 yr old birthday on those caps, so while this wouldn't be the problem of your weak reverb, it does show you've got some caps, one which is definitely leaking poop out the vent hole. Time to replace them.

Thanks for that. 220uF at 500v is a weird cap to find. On mojo musical the closest I found was a 220uf at 350v. Anyone know of a place that sells the 220uf at 500v?

[cluster]

don't know if I should start a new thread but does anyone know how to test a reverb transformer?? Do I disconnect the leads and apply a 9vdc battery to one side and measure the other??

[cluster]

Is this just a standard reverb driver or do I have to order a special part.

assume this will work...

https://www.amplifiedparts.com/produ...t-3-12-w-8-ohm

[Helmholtz]

don't know if I should start a new thread but does anyone know how to test a reverb transformer?? Do I disconnect the leads and apply a 9vdc battery to one side and measure the other??

What makes you think that the reverb transformer is not O.K.?

Did you re-check DCR values (see my post #3)?

Transformer function cannot be tested with DC. You might connect the primary to the 6.3V heater supply and measure the secondary voltage. This should be around 0.1V AC.

[Chuck H]

Thanks for that. 220uF at 500v is a weird cap to find. On mojo musical the closest I found was a 220uf at 350v. Anyone know of a place that sells the 220uf at 500v?

In the schematic those 220uf caps are only rated at 285V. You'll be fine with 350V parts and that's what most people use to replace them.

On that same note, replace all those caps. Some guys would choose to replace only a cap that is obviously failing. But those caps are 40 years old and have an expected service life of probably half that. If one is belching it's innards I think it's reasonable to replace them all.

[cluster]

What makes you think that the reverb transformer is not O.K.?

Did you re-check DCR values (see my post #3)?

Transformer function cannot be tested with DC. You might connect the primary to the 6.3V heater supply and measure the secondary voltage. This should be around 0.1V AC.

Just checked again. With transformer in place I got:

blue/red = 1.917 KOhm

black/green = 1 Ohm

So, does this look like the tranny is ok?

[cluster]

In the schematic those 220uf caps are only rated at 285V. You'll be fine with 350V parts and that's what most people use to replace them.

On that same note, replace all those caps. Some guys would choose to replace only a cap that is obviously failing. But those caps are 40 years old and have an expected service life of probably half that. If one is belching it's innards I think it's reasonable to replace them all.

For sure. I had that in mind. Thanks for the reminder.

[cluster]

Well.... I finally figured it was indeed the tank. After pulling my hair out I decided to revisit the tank thing using a new tank from my reissue super that I have here. Well, it worked. So, I opened up the suspecting and found the culprit. Broken wire. Doubt that is fixable. Looks like a new tank is in order.