Gibson GA-35 RVT Lancer Reverb transformer

[vibrovox7reverb]

I'm not sure if this thread belongs in the repair section, but I couldn't figure out exactly where it should go.

I'm currently modifying the amp in the title, and I was planning on putting in a Fender style reverb section, but this particular amp that I was able to buy cheaply off of eBay because it wasn't working...only has 2 wires coming from the transformer which is not only incorrect for a Fender style amp, but also for this amp as well.

It does however have 2 tabs coming from the reverb transformer that I assume are the taps for the missing parts of the amp, but I don't know how to identify which side of the transformer either the taps or the wires are supposed be: primaries, secondaries, the primary that gets grounded, the secondary that goes directly to the input side of the reverb tank, or anything of the sort.

If I had left the wires in from before, or made a note of what the two wires were connected to then I would have a better idea of where the other 2 tabs should go, and I'd know where the two remaining wires were supposed to go as well...live and learn.

So my question is if it would be possible to measure across the transformer and figure out which tabs and wires were which part of the transformer.

In case anyone has any experience with these amps the two wires that I still have are brown (maybe yellow), and blue which might help you to tell which part of the circuit these two wires are connected to.

[imaradiostar]

Only two wires seems to indicate a choke. I've seen transformers with three wires and one soldered to the steel transformer bracket, but no output transformers with only two leads.

Have you looked at the chassis layout on schematic heaven? Google it and take a look if you haven't.

Brown and blue are generally opposing plates but that's usually on a push-pull transformer. Are you 100% certain you're looking at the right one? It should have four leads.

jamie

[vibrovox7reverb]

Yes, I've verified through schematic heaven where the choke, reverb transformer, and phase inverter/driver transformer (I don't really know what these are called, but they perform the duty that a normal phase inverter tube does) are located and what I'm looking at is T4 on the chart.

It doesn't have the usual wires one side, but instead it has two tabs while the other side has two wires. I have verified now that the two wires it does have are the secondary wires, and the blue goes to the plate of the driver, and the brown to ground.

This means that the side I'm wondering about should be the primary, but I don't know which tab is which of the primary, or if perhaps the tabs aren't even connected internally, and someone clipped the wires really close requiring a new transformer.

If I have to get a new it's not too big of a deal as they're usually about 30 bucks give or take, but I would prefer to know which side is which as this would keep from having to spend money and wait on a part.

I can check to see if wires were supposed to be coming out of it, but it doesn't seem like that's the case. So out of curiosity, if I were looking at the schematic and the top wire on the secondary side was blue...would the top primary wire be adjacent to the blue wire on the physical transformer?

Like


Blue(top primary wire on schematic)-------3 II E-----top secondary wire from schematic
Brown(bottom primary wire on schematic)------3 II E-----bottom secondary wire from schematic

Would the wire that is labeled "top secondary" actually physically be towards the same side of the transformer as the blue wire just adjacent to it?

Edit: the 3 II E was supposed to look kinda like the schematic drawing of a transformer.

[Enzo]

Let's get our terms straight. The primary side is the side that gets driven, the secondary side is the output. In this case the secondary connects to the reverb drive coil.

The primary is the side that connects to the tube. Blue is for plate, and the blue wire to the plate of the tube sounds right. It could be brown, but I'd wager the other wire started life red instead of brown. In any case, it does not go to ground, it goes to B+. Otherwise there would be no plate voltage on the tube. The B+ node this connects to says +252v on the schematic. Follow the wire from the transformer down and over aqnd back up... 252.


If you are unsure which wires and tabs connect, use an ohm meter to find which ones have continuity.

That is your two wires. They would not likely have put B+ on bare tabs. That kleaves the two little bare tabs. Those are the secondary and there used to be a cable connected there running down to the input jack of the reverb pan. The input of the reveb pan is a low impedance, just like a little speaker would be. SO the wires don;t need to be shielded. The return wires from the pan output MUST be shielded, but not the drive end. It CAN be shielded there, but need not be.

This is a reverb, we are driving springs, polarity is not important. Connect the two tabs to the reverb pan either way.

[vibrovox7reverb]

Yes I think I referred to the each side as the primary at one point, and I said the brown wire went to ground when it actually receives the B+. Thanks for explaining the two tabs for me...the amp came without a reverb tank or any wires from the reverb tank, so any wire that went to the tank or transformer from the tabs was gone. Thank you so much, I was afraid that I'd have to get a new transformer. Merry Christmas

[drewl]

I have a GA30RVT on the bench, just as Enzo explained, the secondary "tabs" are on the top of the transformer.
I've used standard Fender type reverb transformers in these amp also, and they work fine.