JMP and Power Transformer Question

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JMP and Power Transformer Question

Post by kfowler8 » Tue Jul 02, 2019 12:50 pm

Hi guys,

I'm in the process of building a JMP/JCM 800 2204. I have an old 1968 Traynor YVM-1 PA head. This amp has 50 watts, 3 12AX7s, and 2 EL 34s. So pretty similat spec wise to my build. Other than some of the original mustard caps, I'm using the Hammond PT, OT, and Choke off the Traynor. All three are in good working order.

Some questions:

The PT has the following wires coming out of it:
- 2 Black (primary)
- 2 Red (secondary/High Voltage)
- 2 Green (filament)
- Green/Yellow (filament center tap)
- 2 Blue (bias supply)

For the two black primary wires, I assume it doesn't matter which I hook up to the fuse and which to the power switch? So basically there's no defined common or hot lead?

The red HV wires have no center tap. As I understand it since I'm running these to a solid state bridge rectifier, this is not needed, correct?

I won't need the 2 blue bias wires for this build. What's the best way to cap them off? Snip any exposed wire off and heat shrink the ends?

In the MetroAmp plans, there's an 8.2K 1 watt resistor in series with a 10K voltage dropping resistor going into the choke. What's the purpose of the 8.2K resistor? I don't see this on any of the stock JCM 800 2204 schematics.

Coming out of V1b pin 6 is a .022uf coupling cap that says you can use a .0022uf instead. As I understand it the lower .0022uf filters more the bass and allows the amps to focus on the mids and highs for a smoother distortion. Curious as to how much of a difference this makes?

Thanks so much for the help!

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