Vintage Club 60 Reverb Problem

[plexi50]

The reverb cables are good. The reverb is present but fades out after 20 seconds. Tried 2 other tanks but that is not the problem. I have replace a TL072 OP amp in the schematic and still have the same problem. Thinking Tip32C (Q14) (Q13) MPAS06 are next

[PRR]

First question in ANY lost reverb: bad drive or bad recovery?

Recovery is easy to check... put your finger on the reverb return, it should hum LOUD.

Drive can be checked by substituting a speaker or headphones for the reverb tank input. In classic Fender a 4-8 ohm speaker is perfect. Dummy-load the main output so you can hear the plink in the reverb driver and test speaker.

In this case we don't know the reverb tank impedance, and we might suspect it isn't 4-8 ohms. You could meter the tank and see if it is a few ohms, a hundred ohms, or many hundred ohms.

There's test-point voltages on page 1.
 Did you check the DC voltages? Which ones go way-wrong after 20 seconds?

In general I would not suspect a tank... tanks don't heat up. (Except this one does.) Likewise the chip "usually" will work or dont-work. Bad solder joint is always possible, but some poking should provoke it to cut in and out, and you know that dance.

I figured-out some of the "right" voltages. Not same-as the test-point numbers, but it is a funky plan and some variation is expected.

I said tanks don't heat. This driver runs _DC_ through the tank. That's barely kosher. The tank coil _will_ get warm. So it very well could be a broken lead inside the winding, which touches when cold but opens when the coil expands.

This driver is hyper-fussy about tank input DC resistance. I figure it needs to be 100 ohms. A few-ohm or 1K winding will throw the power transistor out of bounds, no signal.

If the tank "may" be burned-open, replace it with 100 ohms and see if the DC voltages now hold near nominal.

[plexi50]

Im going to test the voltage points tommorrow. If i touch the recovery cable i get a hum but not real loud. Then after closer to 5 seconds it will fade away. It wont come back for 1-2 minutes. The reverb tank that was in it is bad and the transducers are open as well

This amp had a bad PT and i had to get one built from Mercury Magnetics. After powering on the amp i have reverb but it is very weak. The amp works for roughly 20-25 minutes before a reverb voltage crackling whistle develops with the chassis on the bench. As soon as it starts to whistle i can lift the chassis off the bench and blow on TIP32C and the whistle stops immediatley. So i figure i have a thermally sensitive part in the reverb path

Sorry about all the explaining. This amp has another problem where the front panel channel switching doesnt work as well
Not a friendly amp to work on so far. I'll check those voltages and get back to you

[plexi50]

Might as well get this figured out today. This is my diagram and voltages. This is without a tank connected

All resistor values are within specs except: I can not get a correct reading on R101-22K & 102-10K / In circuit?

DAM THIS IS FUN!  

[sluckey]

If i touch the recovery cable i get a hum but not real loud. Then after closer to 5 seconds it will fade away. It wont come back for 1-2 minutes.

That statement makes me want to look at the recovery circuit.

But...

This amp has another problem where the front panel channel switching doesnt work as well

...this statement makes me want to check the +12v power supply. Multiple problems, look for a common cause first.

Troubleshooting any ss circuit should always begin with checking the power supplies.

[plexi50]

Steve i have a problem with remembering which is the input and which is the recovery stage.  What is a good way to get this stamped in my brain once and for all. I dont do a lot of reverb work.

[sluckey]

Put your shotgun down and just look at the schematic.

[plexi50]

Put your shotgun down and just look at the schematic.

[John]

Put your shotgun down and just look at the schematic.

I'm gonna start making a compilation of your and PRR's replies! 

[sluckey]

Bam, bam! You're shooting too low. You just shot the PI. Look at the top of the page. But first, look at TP25 and TP26 on page one.

[plexi50]

Ok/ I checked TP25 & TP26 diodes and IC2/IC3 circuit. Diodes read good
I put new voltage regulators in place yesterday
I just noticed that the regulator numbers are different on the schematic than the ones i removed from the board
But they both have the same input and output voltage specs
Removed  L7812ABV (IC2) & MC7912CT (IC3) and replaced with the same yesterday

Hum! Man do they get hot. Those tin heatsinks dont do much to dissapate heat
Back in a bit

[sluckey]

I just noticed that the regulator numbers are different on the schematic than the ones i removed from the board
But they both have the same input and output voltage specs

There's a MAJOR difference. 7812 is a PLUS 12v regulator. 7912 is a NEGATIVE 12 v re3gulator. What voltage did you read at the test points???

[plexi50]

I just noticed that the regulator numbers are different on the schematic than the ones i removed from the board
But they both have the same input and output voltage specs

There's a MAJOR difference. 7812 is a PLUS 12v regulator. 7912 is a NEGATIVE 12 v re3gulator. What voltage did you read at the test points???

IC2 is positive & IC3 is negative. Yeah i know im always forgeting about - &+

IC2 L7812ABV has +12.00 VDC & +19.70 VDC

IC3 7912CT has -12.00 VDC & -19.93 VDC

[PRR]

> This is my diagram and voltages. This is without a tank connected

I can see the tank is out 'cuz TP20 is slammed to +12V. Put in the tank, or 100 ohms, and measure again.

> Sorry about all the explaining

No, you should have included that in the first post. I'd assumed there was no complaint except sick reverb. Now we know there are multiple problems (including the clean/dirt switching which seems to affect reverb).

[plexi50]

Ok here are the new voltage with the tank installed
Also i just noticed that when you turn up the FX Loop level pot the noise gets much worse
This is with no cable pluged into the FX Loop

I was thinking weather or not the channel switching could be causing this as well

This is a mess but doable. I appreciate all of your help

[PRR]

Q14 is surely blown.

This doesn't explain your other symptoms.

[plexi50]

Thanks  PRR. I ordered TIP32C and some other parts friday. The channel switching has eluded me so far. The channel switching works with a footswitch but i can hear the volume for the dirty channel is lower when using the footswitch

I have dirty channel on at all times. No clean channel unless using a footswitch