Help with a JCM 2204 Build and PT Question

[kfowler8]

Hi guys,

I'm building a clone of a JCM 800 2204. I'm using parts from MetroAmps and Mojotone.

For PT, OT, and choke, I'm using what I've salvaged from a 1968 Traynor YVM-1 PA head. This was a 50 watt head with three 12AX7s and two EL34s. So very similar to the JCM. The iron is Hammond so they're pretty stout.

Several questions on the PT. It has two black wires (primary), two red wires (high voltage AC), two green wires (filament), one green/yellow (filament CT), and two blue wires (bias).
- I assume it doesn't matter which black wire I hook up to the fuse and which to the power switch? There's basically no designated common or hot, correct?
- The red high AC wires has no center tap. I assume this is OK since I'm running these to a solid state bridge.
- Since I don't need the two blue wires, what's the best way to cap them off? Heat shrink on the end?

The generalJCM 800 Schematic online has the 10K 1 watt resistor coming off the choke. Assume this reduces voltage. The MetroAmp plans have an additional 8.2K 1 watt resistor in series with the 10K. What's the purpose this additional 8.2K resistor?

Thanks for your help!

 

[RAG7890]

I'm sure someone here will answer the question but if I were you I’d send Hammond an Email with the Serial No.'s and Pics & ask if they can help with a Wiring Diagram on the Iron Set: -

Contact Us

Hammond Manufacturing is a leading manufacturer of industrial enclosures, electronic enclosures, racks & rack cabinets, transformers, outlet strips and climate control products.

www.hammondmfg.com

My 2c FWIW.

 

[Cjsinla]

The black wires have no polarity afaik, but the red wires should have a center tap to ground. I built that Metro/Valvestorm kit with the rectifier bridge and my Classictone PT has a red/yellow tap.

Heatshrink is fine for unused wires.

The 10k + 8.2k is used to drop the high voltage that goes to the plate resistors for the phase inverter. I’ve seen some guys play with those voltages. It probably depends how much voltage you have leaving the rectifier. My PT has 312 per side. You will have to figure what voltage you need after those dropping resistors. One 2204 schematic I saw says that there is 390 volts to the plate resistors and 250 volts at the PI plates.

 

[kfowler8]

The black wires have no polarity afaik, but the red wires should have a center tap to ground. I built that Metro/Valvestorm kit with the rectifier bridge and my Classictone PT has a red/yellow tap.

Thanks! As I understand it, using a solid state bridge rectifier negates the need for having a CT on the reds. I know there's a way to make an artificial center tap but I believe it's just duplicating the diode process in the bridge rectifier.

 

[kfowler8]

Man, kudos to Hammond. I emailed them this morning asking for specs on the PT and they've already responded. Great Customer Service

 

[RAG7890]

Man, kudos to Hammond. I emailed them this morning asking for specs on the PT and they've already responded. Great Customer Service

Man, kudos to Hammond. I emailed them this morning asking for specs on the PT and they've already responded. Great Customer Service

That is awesome...............& no guessing with the original PT Specs in hand.

Good luck.

 

[V2]

All good. no CT required on the HT (red) secondaries when using a bridge rectifier.