Epiphone Pathfinder

[goldtop5]

I have an Epiphone Pathfinder tube amp combo that has a problem with the reverb. I replaced the 6c4 tube and still the problem persists. When you bang on the cabinet, you can hear the reverb springs through the speaker. I can only hear just a small bit of reverb ambience when I plug a guitar into the amp, and that's with the reverb control turned all the way up. What could be the problem?

[goldtop5]

Here is the schematic for this amp, by the way.

[Jack Hester]

Have you swapped V1 with V2, or V4? Half of V1 is the 1rst stage of the Reverb Driver. As you've already traded out V3, I'd say a tube swap of the 6EU7's is the next step. V4 is your Phase Inverter and your Tremolo oscillator.

Jack

[Mick Bailey]

You can hear the springs, so the output transducer and recovery circuit is working. If tube swapping gives no result then check if the driver circuit is providing enough drive and the transformer is good. A reverb tray takes a fair bit of power to drive and a way of checking is to unplug the tray input and connect an 8 ohm speaker. You should hear your guitar through that. If so, then the tray is bad. If not, then either the driver circuit or transformer has a fault.

[52 Bill]

Hey welcome to the place.

The first thing that I always test is the reverb tank connections. They are the weakest link in the entire system.

As you can hear the springs rattle when you hit the amp, you know that the output side of the tank is working as it should. Now you need to test the input side. Do you have an ohmmeter? If you do, you can read the resistance across the input coil and see if it is still connected.

First test would be to make sure that the RCA plugs going into the tank are clean and tight. Use a little DeoxIt on the connections and twist the plugs in the jacks to burnish then clean. Look inside the metal tank itself and check the two small wires that connect the transducer coil with the RCA jack for breaks.

If you remove the tank from the case, be careful of the wires that connect the tank to the reverb drive transformer. If you pull too hard, the terminals on the transformer can be pulled out of the transformer winding.

Let us know what you find out.

[TimmyP1955]

Most likely a broken wire (or two) in the tank - a very common failure. In about 1 out of 15 or 20, the transducer is toast and the tank has to be replaced.

[Mick Bailey]

I rewind transducers on older amps if the owner wants to maintain originality, and sometimes just to get the job out of the way rather than wait for parts. If there's some faint reverb then the transducer is probably OK. Sometimes the driver transformer can suffer a shorted turn in the primary and severely reduce drive.

A straight resistance check on the tray's RCA sockets will establish if the transducers are good.

[goldtop5]

I used deoxit to clean the RCA jacks. I even tried a brand new reverb tank. It still does the same. We ordered new pair of 6EU7s that I'm going to try.

[52 Bill]

We ordered new pair of 6EU7s that I'm going to try.

Did you try as Jack suggested swapping the 6EU7 tubes around? Probability is that if none of the existing tubes gets it working, new tubes will not be the answer.

How do the voltages on the tubes compare to the schematic?

[g1]

The reverb control is in the send side of the circuit, that would be a prime suspect. As would be the driver transformer, which you could test with a speaker as Mick suggested in post #4, but you would need to know there was signal at the plate of the driver tube.

[goldtop5]

Update. We got the new 6EU7s in. I installed them, but the problem still persisted. I think that little bit of reverb was the vibration coming from the amp when I play through it. So I focused my attention on the reverb transformer. I removed it from circuit, tested it with a vom, and it read wide open on both sides. Could this part be purchased from the manufacturer regardless of its age? Or could you use a generic?

[52 Bill]

The transformer should be marked E-6400. Gibson will not have a replacement. Mercury Magnetics lists a replacement for $55. Some others here have said that a basic Fender driver transformer will work as a replacement.

[goldtop5]

Update: We ordered a fender reverb transformer off of ebay for $25. I swapped out the old with the new. The reverb is now working.