Gibson GA-15RV power transformer

[lowell]

Hey all,

I have one of these on my bench with a bad power transformer. I ordered one from Mercury and they told me that this one will work. It’s APS TRACE-VEL-P.

I’m almost done installing it, when I came to realize there is no pair of orange leads. In the amp on the bench there is a pair of orange leads that feed a fuse, called FS4. It’s a 1 amp fast blo fuse. Which seems to me as though it would be some sort of heater circuit… but the main 3.15vac heater wires are gray. And I connected them where they go.

I had to get out the angle grinder and cut a square for this PT as it’s the flat laying type.

here is the schematic: http://www.prowessamplifiers.com/sch...V_complete.pdf

I’m going to attach some pictures of the Mercury wiring diagram and the amp that I have on the bench.

can you all please assist me in wiring this PT? I cannot find FS4 anywhere on the schematic so I can’t figure out what it’s for or what the orange leads are for.

[Helmholtz]

FS 4 is on schematic sheet 2/2.
Orange wires should belong to the 24VAC winding.

[g1]

Lower left area of pg.2 of schematic. It's a 24VAC winding. (TX6 and TX7)

You need a PT for the 'gold tone' GA-15RV from the 90's.

[g1]

Actually, the Trace Velocette is pretty much the same (see attached), so that transformer should have the winding.
What color windings does the transformer have, or is there a datasheet with it?

[lowell]

Actually, the Trace Velocette is pretty much the same (see attached), so that transformer should have the winding.
What color windings does the transformer have, or is there a datasheet with it?

Thanks all, yes the wiring diagram is attached in my OP. There are no orange leads and no “extra” leads that I don’t know what to do with.

I’ve also sent this to Mercury for assistance.

[g1]

Maybe there was a different revision of the Gibson and Trace amps that didn't have the low voltage supply for solid-state stuff.
I was going to suggest one of their Vox AC15 PT's that have a low voltage winding, but they all have center-tapped high voltage winding so they wouldn't work for the GA-15RV as it has a bridge rectifier.

[lowell]

Yep… pretty strange! Important note here: there is no reverb transformer. The verb is run with solid state devices. Perhaps the revision was just that… and they needed the low V windings.

I’m sure I can find a suitable 1A transformer for that. If you have any suggestions please save me time searching, suggestions welcome! A toroidal would be fine as well. 1A 24v secondary.

Mercury staff are all on holiday leave until after the new year.

[lowell]

Perhaps a furnace transformer would work!

40VA 24vac

https://thefurnaceoutlet.com/product...caArXPEALw_wcB

[lowell]

https://www.mouser.com/ProductDetail...GGdituEA%3D%3D

thats a vertical mount

here’s a toroid but I’m surprised how big it is! (That’s what she said). 3” diameter!
https://www.antekinc.com/an-0225-25va-25v-transformer/

one from hammond
https://www.hammfg.com/part/PHC25JGA?referer=1051

[g1]

Also Hammond BE2G (546-BE2G at mouser)

[Jazz P Bass]

Also take note that V1 & V2 heaters are running off the low voltage dc supply.

[g1]

That's really the only significant current from the 24V winding. But still only 150mA with the heaters all in series like that.
So with that and the IC's, I don't see why you would need more than half an amp max., or a 12VA transformer? Heater turn on surge?

[lowell]

Good catch guys. I’ll look for a 24vac 12VA power transformer.

[lowell]

I decided to go with this one from digikey

https://www.digikey.com/en/products/...AZSK8JIALoBfIA

I really wanted to find something smaller than 3” long but it would seem that that size is required from a physics standpoint. I guess perhaps it all boils down to total VA, so even 24v at 500ma is a 3” laminated transformer. I guess it’s possible they just use whatever common bobbins/magnets they have in stock for production so maybe they save on production by using one size for a specific range.

[Jazz P Bass]

Not bad for 18 bucks.