90s Super Reverb issues

[jkey04]

A friend of mine gave me his 90s model Super Reverb to troubleshoot. When playing thru it at any volume it has a grungy distorted sound. Kinda like a harsh blocking distortion. Also, neither the reverb nor term work.

I changed all the tubes and that didn't make any difference. I've built several tube amps, but never had much experience with troubleshooting bad components. Could this possibly be a bad OT? That wouldn't explain why the effects don't work though.

Any thoughts?

Thanks!

[Stevem]

If the reverb pan and it's drive transformer are good, and the 12at7 that drives that transformer is good than the reverb will work without the foot switch provided that the 12ax7 in the V4 location is good.
If you unplug the RCA cable going into the reverb pans out out jack and touch the end of the cable with the reverb turned up you should hear a buzz which would mean that v4 is working.
The input side of the pan being feed by that small transformer is really just a 1 watt amp, and you can hook that up to a speaker and hear if and how well that side of the reverb system is working.
You can pull v1 out if the normal channel if that channel works and place it in the V3 and V4 socket to test for tube issues in the reverb circuit.
The tremolo however needs the ground connection from the foot switches reverb RCA plug and or jack to be good otherwise the tremolo will not work.
Also the the item called the opto coupler in the amps trem section could be bad.
Low volume and distorting could be a output stage issue and or a power supply issue, have you ruled out the speakers by playing the amp thru different ones?
how do the two resistors look mounted on top of the output tube sockets, does the big one (470 ohm) have over 400 volts on each side of it, and does the small one (1.5k half watt) have a negative 45 volts or greater at each end?
The amp being a 1990 model may need power supply filters as these where for crap at best and if one is going leaky than I f you pull the cover on the filter cover case you may well find one or both of the power supply node dropping resistors is burning up and this could well the the root of your issues along with the filters that started the whole mess!

[jkey04]

Just wanted to give an update here. Thanks for the reply Stevem.

I finally had some time to take a look at this Super and found that the issue causing the low volume and trashy distortion sound was a bad plate resistor on one side of the phase inverter. I swapped it out and she sings beautifully now!

The tremolo works as should, but the reverb does not. I appears that the reverb tank is bad. I read ~2ohms across the input, but the output of the tank reads open. After some research on reverb tanks, it looks like the MOD replacement seems to be a good one to buy. Any other suggestions troubleshooting-wise or on what reverb tank is best?

[martin manning]

Here's a case where using 1W plate resistors is a good idea. High voltage, higher current 12AT7 PI... The issue isn't the voltage, it's dissipation.

[xtian]

After some research on reverb tanks, it looks like the MOD replacement seems to be a good one to buy. Any other suggestions troubleshooting-wise or on what reverb tank is best?

I bought both MOD and Accutronics tanks with the same spec. Both sounded good, but different. Brighter/darker, longer/shorter decay. Don't remember which! Anyway, cheap, easy to swap--buy both!

[Stevem]

It's the Mod brand that tends to sound on the dark side, may be not bad for a early Ampeg replacement, but not for a Fender if ya ask me!

And thanks for the up date!