Fender Quad Reverb - No Reverb - Help

[ilcaccillo]

Hello I'm trying to fix a Fender Quad reverb but I'm stock and loosing my ideas.
The Reverb Doesn't work, and I tried all I could to make it work and can't figure out what's going on.

I Know the Recovery circuit and reverb PAN are good, because When I tapped the reverb tank I heard the clangy mechanical spring sound, but to test also the input of the Pan what I did was used another amp , a Twin Reverb with a dummy load, as I send the reverb signal of the Twin Reverb into the Quad Reverb reverb tank input.
So basically the Twin Reverb was feeding the reverb Pan and recovery circuit of the Quad Reverb amp. Well both the PAN and Recovery are fine because with the Twin reverb driving it I hear perfectly good reverb on the Quad Reverb.



Then I went for the driver circuit,
Reverb transformer measured 1K2 primary DC resistance and secondary 30 ohms DC resistance. Normally the secondary should be around 1 ohm, so I replaced the Reverb transformer for a new one with the right DC measurements.

Reverb still doesn't work.

I measured the voltage at the reverb driver tube pate and I have 470 volts.

The 12AT7 that came with the amp measured fine in my Hickok tube tester, but I replaced it anyway for a new 12AT7 and
Still No reverb

I injected audio signal at the input and probed around the circuit and I have signal going into the reverb driver and signal also at signal at pin 6.

I replaced the 1 Meg resistor , 25uf/25V cap and the 2200 resistor.

Checked continuity with the schematic, everything tests fine.

Still no Reverb.

Let me know that I did all the tests without the footswitch connected and checked in every test by taping the reverb tank do see if the output signal of the tank was being amplified and mixed into the output.

I also tried to have the Quad Reverb drive the Twins Reverb PAN and recovery circuit and it didn't work, only a really week signal came out.

I replaced the Tube Socket for a new one.

Still no Reverb.


I'm sorry but I'm in a Dead end I don't really know what I can do more.

If you have any ideas, suggestions to help me out fix this issue I would be highly appreciated.
Thank you so much






Schematic

[ilcaccillo]

I forgot to say something that might be really important,
With the signal probe the signal I get at V3 Pins 2-7 (input) is much stronger than the signal I probe on Pin 1-6 (Output) So it seems the tube is not amplifying.
This happens regardless of the tube used and before and after the new tube socket




DC Voltages V3 - 12AT7 - Reverb Driver

PIN1 472V
PIN2 0.1V
PIN3 9V
PIN4 0
PIN5 0
PIN6 472V
PIN7 0.1V
PIN8 9V

Heater Voltage between 4-5 and 9 - 6.89 AC volts

[Enzo]

OK, so the pan works. Easiest test would have been to measure resistance through the drive side transducer, it iwll either be open or be OK.

You have a Twin reverb that works? Why not take readings around the drive transformer ther for point of reference?

If the transformer is OK, you replaced it, then I might think the reason my plate signal was so small was that the transformer secondary was loaded. Unplug the cables to the pan from the chassis jacks. Now how does the plate signal look? What level signal is on the empty jack? Will that jack drive a small speaker? Check the cable for shorted condition, or just sub a different pair of cables. Is teh chassis jack shorted? Pull the wire off the center pin and see if sig lis on the tranny wires.

[ilcaccillo]

Thanks Enzo, I was able to solve it.

Sorry,
After all this work it was just RCA input jack (actually the output from the amp) that had a bad Chassis connection.
Really Simple

Oh Well,
thanks it working now