Crate GT500H/Vintage Club 50 no reverb

[lo-watt]

Looking for a little advice. Amp is working well in all other ways except reverb. Tested resistance of tank 20 something ohms on one side,200 something ohms on the other. Both cables test OK for breaks. It has a SS reverb circuit im pretty sure. Any advice?

[The Dude]

If memory serves, the Gt500H is virtually identical to the VC50, so this schematic should be close if not exact.

http://trentstuff.com/Crate/crate_vintage_club_50.pdf

If you have a scope, just follow the signal and see where it isn't.

[lo-watt]

Yes this is just the Vintage Club in head form. Sorry for not posting the schem. I tried another known good tank,no dice. When i turn the Reverb Level knobs up,all i get is a hum that gets louder. If i bang the tank i do get a slight crash through the speaker,but not much.

[lo-watt]

Sorry,no scope just a DVM.

[glebert]

If you pull the RCA plugs off the tank you should get some good hum/pop when you touch one of them (the return cable).

The VC amps are pretty notorious for cracked solder joints, so maybe be on the lookout for those. I have a VC30 that I am just going to reflow everything on because I know I have a crack somewhere.

[The Dude]

My first thought is a switching jack issue. Run a plug in and out of the foot switch jack a couple times and see if starts working. Or, plug in the footswitch and see if you can get reverb using the foot switch.

[lo-watt]

I did look for bad solder and put my burnishing tool through the Cliff jacks. Also checked the header that connects the circuit to the reverb circuit.

[glebert]

My first thought is a switching jack issue. Run a plug in and out of the foot switch jack a couple times and see if starts working. Or, plug in the footswitch and see if you can get reverb using the foot switch.

Don't think reverb is switchable on this.

[The Dude]

Not "per se", but is switched with the channel switch for the appropriate and associated reverb level control. There's not a separate reverb footswitch, but if you look at TP 10 & 11 on the first page, they feed a pair of FET's on the second page that are switched for each reverb level, depending on which channel is selected. Don't ask me for details. It was a long time ago, but I remember battling this problem in the past and it ended up being the switching jack.

[lo-watt]

Im familair with the issues of these amps and thier Cliff jacks. I was hoping that my burnihing tool would at least get it going. After loking at the schem,are there any other voltages besides the tes points i should be looking for? Like Op amp 15vdc? or JFET?

[glebert]

Not "per se", but is switched with the channel switch for the appropriate and associated reverb level control. There's not a separate reverb footswitch, but if you look at TP 10 & 11 on the first page, they feed a pair of FET's on the second page that are switched for each reverb level, depending on which channel is selected. Don't ask me for details. It was a long time ago, but I remember battling this problem in the past and it ended up being the switching jack.

Of course, because there is separate reverb controls for each channel, which I should know, since I have a VC30 and a VC50.

[lo-watt]

Any more thoughts on this repair?

[The Dude]

Sans scope, you can inject a test tone and follow signal using the AC volts function of a DVM.
Check DC voltages on IC1. Is there voltage on pins other than 4 & 8 that might indicate it is shorted? Is there supply voltage on pins 4 & 8?