Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: waldner on November 19, 2023, 02:04:07 pm
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I get no reverb on my Rockerverb mkII. The only schematic I can find is for the mkI, but I think the reverb portion is the same.
When I shake the tank I get spring noise output through the amp.. I changed tubes several times and no change. When I checked the tank impedance I get the appropriate higher impedance (200+ ohms) on the output side and about 1 ohm on the input side. So I think the tank is good.
When I checked the cables for continuity, I measured a short on the input cable between the hot and ground connection. When I then disconnected those cables and measured at where they connect at the circuit board I get the same short (continuity).
Not sure what to do next as it seems my tank works, cables are good, tubes are good, but I'm only getting output from the tank and nothing going into it. On the image below from the schematic it appears that the two points on the circuit board where the reverb hot and ground are connected for the input to the tank, are tied to TX13 and TX14. When I check continuity between those two I get a short. I also can't see on the schematic where TX13 leads to? It doesn't seem to go anywhere.
Any help would be appreciated.
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...where TX13 leads to? It doesn't seem to....
The TX pins go to the Reverb Transformer, which you did not mention at all. The TX13 pin goes to the REVERB1 pads and coax to the tank.
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Measure the vdc on each side of the reverb transformer primary (red and blue wires - TX11 and TX12 on the schematic). What do you get?
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Doh :embarrassed: Of course they go to the transformer! Thanks PRR. So the signal coming from the plate of V6 goes to the primary of the reverb transformer and then the secondary from the transformer goes to TX13 / TX14. From there to the input of the tank.
I just can't figure out why I get no signal going into the reverb tank but seem to get spring noise coming out. :help:
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Measure the vdc on each side of the reverb transformer primary (red and blue wires - TX11 and TX12 on the schematic). What do you get?
I get about 30vdc on the red and on the blue it starts at 4vdc and starts descending.
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Are those measurements with the amp powered on and not in "standby"? If yes, that's a problem. Should be much higher. What vdc do you measure on each side of R2 (15k connected to red wire/TX11) ?
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Are those measurements with the amp powered on and not in "standby"? If yes, that's a problem. Should be much higher. What vdc do you measure on each side of R2 (15k connected to red wire/TX11) ?
I think I may have found a difference between my mkII and the schematic for the mkI because there is no 15K 1W resistor located at R2. As a matter of fact, there is no resistor at all at R2, which is in the area of the bias adjust circuitry. See pic.
I looked around the board and don't see an equivalent resistor either.
I also re-measured with the amp on and not in standby and I'm still getting the meter jumping around, mainly descending starting at about 10vdc at TX12 (blue)
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Do you still get the same readings on TX11/Red? While you're at it, what's vdc on pin 1 and 6 of V5?
A good clear pick of the PCB around the reverb transformer connections and V5 might help too.
Edit to add: Looking at the schematic there are least two different R2. One in the bias supply and one connected to TX12.
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Do you still get the same readings on TX11/Red?
A good clear pick of the PCB around the reverb transformer connections and V5 might help too.
Sorry I should have checked both. I get 388vdc on the TX11 Red now. Below are two pics that I hope will show the pcb in that area. Thanks!
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If you have 388 vdc on the red and you should have about the same on the blue. Disconnect the red and blue wires from the PCB and measure resistance from red to blue. What do you get?
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> I just can't figure out why I get no signal going into the reverb tank but seem to get spring noise coming out.
If you shake the springs, they WILL make a sound. Don't have to have an electric shake if you have a mechanical shake.
Hay-wire a speaker or headphone to the REVERB1 coax. Can you hear guitar? Why not?
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Ok, I just left my shop for tonight and will continue and try those remaining recommendations tomorrow. Thanks again Deric and PRR for taking the time to help me troubleshoot.
:worthy1:
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If you have 388 vdc on the red and you should have about the same on the blue. Disconnect the red and blue wires from the PCB and measure resistance from red to blue. What do you get?
Ok, measured again with amp fully on and still getting 388 vdc on the Red and only about 9 vdc on the Blue. Possible issue with the reverb transformer?
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Looks like you have a bad reverb transformer. Disconnect the red and blue wires from the PCB and measure resistance. What do you get?
FWIW - I don't work on a ton of amps but I've come accross 2 bad reverb transformers in the same amp. Both had an open primary.
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Looks like you have a bad reverb transformer. Disconnect the red and blue wires from the PCB and measure resistance. What do you get?
FWIW - I don't work on a ton of amps but I've come accross 2 bad reverb transformers in the same amp. Both had an open primary.
I get zero when I disconnect the Red and Blue and measure resistance. Maybe I need a new transformer. Do I need to get this specific one from orange or will a similar basic Fender reverb type transformer work?
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As far as I know the only available drop in replacement is the Mercury OR-RV which is what I used. A quick Google search shows this is a very common issue with these amps. It also looks like like several people have used a standard Fender transformer with good results. They do have a different footprint so mounting it may be an issue.
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As far as I know the only available drop in replacement is the Mercury OR-RV which is what I used. A quick Google search shows this is a very common issue with these amps. It also looks like like several people have used a standard Fender transformer with good results. They do have a different footprint so mounting it may be an issue.
Thanks Deric. I just ordered the Mercury transformer.
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Thanks again for the help PRR and Deric. I got my new transformer, installed and have glorious reverb working!
The Mercury was expensive, but a direct replacement that fit the holes in the chassis and had the same wire color codes.