transformer wiring

[Rick1114]

I'm replacing the burnt Power Tranny in my Gibson GA5 (already did a cap job and checked all the resistors). Gibson amps are very hard to decipher because they rarely follwed the schematics from what I've heard, and this amp surely follows that script.

Anyway, I've got all the connections figured out except for two, the Primary center tap (red/yellow) and the B+ sheild (green/yellow). I noticed with the original transformer both of these wires are soldered to pin 7 of the 5Y3. In the Gibson schematic, the Center tap goes to ground and there is no mention of the Sheild (but I've read it usually goes to ground as well).

Since this was an ungrounded amp with a 2 prong plug, were these connected to pin 7 of the rectifier for that reason? I don't want to follow the old wiring scheme without knowing why!

Thanks,

Rick

[52 Bill]

Anyway, I've got all the connections figured out except for two, the Primary center tap (red/yellow) and the B+ sheild (green/yellow).

By "Primary center tap", do you mean the High voltage secondary center tap?

Standard US transformer color-codes would use red for the high voltage secondary with red/yellow as the center tap.

Green is used for 6.3 v filaments, with green/yellow as center tap.

Yellow is used for 5v rectifier filament, which never has a center tap.

I noticed with the original transformer both of these wires are soldered to pin 7 of the 5Y3. In the Gibson schematic, the Center tap goes to ground and there is no mention of the Sheild (but I've read it usually goes to ground as well).

Since this was an ungrounded amp with a 2 prong plug, were these connected to pin 7 of the rectifier for that reason? I don't want to follow the old wiring scheme without knowing why!

Pin 7 of the 5Y3 is not connected to anything inside the tube. They used the pin as a tie point for what probably is a ground connection.

[Rick1114]

By "Primary center tap", do you mean the High voltage secondary center tap?

Standard US transformer color-codes would use red for the high voltage secondary with red/yellow as the center tap.

Green is used for 6.3 v filaments, with green/yellow as center tap.

Yellow is used for 5v rectifier filament, which never has a center tap.



Pin 7 of the 5Y3 is not connected to anything inside the tube. They used the pin as a tie point for what probably is a ground connection.

Thanks for clarifying that - I must not had gotten enough sleep last night. I meant center tap for the red wires (300V) which is labeled as "B+" in the diagram I received from mercury, and the Green/Yello which is labeled as "Shield". They go to pin 7 as well as the negative ends of the filter caps, so that must be the ground. I still can't how this is "grounded" though. There is another wire from pin 7 going to the other tubes sockets and then the volume pot - and even to the pilot light from that connection on the 6V6. Nothing soldered to the chasis I can see and no death cap either....

Anyone know what kind of grounding scheme this is?

[pila]

I believe Gibson built a few different GA-5 type amps, so you may need to research the schematics available to see which one you really have.
I've been looking a "Crest" version of the GA-5 for a build project.

[domocaster]

hi,
I have a Ga 5T, that has an overheating problem, I was wondering if yours was suffering the same problem; is that why you changed the power tranny?
As far as conections go; follow the old conections exactly,you should be fine.
Thanks dom,