old JTM45 power txfr 2 x 6.3vAC windings?

[Alex R]

I have here a very old Tremelo JTM45, to which I am fitting an equally old RS laydown power transformer. I have all the txfr windings ID'd. In addition to the 5v rectifier heater supply, it has two sets of centre-tapped 6.3v windings. Both are of equal-weight wires, using single-core lacquered wires for the AC and multicore for the CT. One set has blue insulation, the other green. One set for the preamp and one for the power tubes I guess. The equal-weight wires lead me to guess they are interchangeable and of equal power rating... unless you know different? Any ideas?

[Alex R]

...or phase them up and connect them in parallel? Anyone know what Marshall used to do with them?

[tubeswell]

it has two sets of centre-tapped 6.3v windings. ... One set has blue insulation, the other green. ... Any ideas?

Hi Alex

Are you sure it was from a JTM45 originally? Have you fired it up yet and measured the VAC across the secondaries?

I think the blue leads could possibly be a separate bias winding, and the PT could've been originally from a 200Wer

http://www.drtube.com/schematics/marshall/200w.gif

[Alex R]

Hiya, and thanks for the response, but yes I have measured the output across both sets of windings and it is 6.3vAC (well 6.6vAC but you know what I mean). It's definitely a JTM45 tranny, an RS. It came with an RS deluxe OT I've already fitted. Way too small to be off a 200W anyhow. I note that MM produce a couple of JTM45 RS clones with dual filament windings, 2.5A each, looks about right for the wire sizes I'm looking at, but I can't find out how they were hooked up in the JTM. I'm guessing in parallel, but there's no coding to help you phase them as I might have expected (it's ok I can scope them instead).

I guess these RS jobs were all-purpose transformers and the split was so you could run the old Brit 6.3v rectifiers like the EZ81 on a separate winding.

[dai h.]

hi,

you might try asking Brian at Marstran. He's reverse-engineered Marshall transformers and might know something, although I don't know if he has reverse-engineered that one specifically.

Marstran.com • Index page

[Two Tone]

one for the power tubes,
the other feeds the preamp

[Alex R]

Thanks! Can I ask if that's an absolute certainty...? I want to get this one right.