1974x ot?

[chuckb]

Hey guys , i have a set of trannies that were removed from a 1974x marshall . they are Dagnall trannies. I need help determining the b+ wire. Normally this is the red wire with a brown and blue, but my ot(DED4910} has a brown,white and a red. sometimes the white is the ct? any help would be greatly appreciated.

Chuck.

[Leo_Gnardo]

I need help determining the b+ wire. Normally this is the red wire with a brown and blue, but my ot(DED4910} has a brown,white and a red. sometimes the white is the ct? any help would be greatly appreciated.

True Marshall (and other UK & European) OT's seldom follow US convention in wire colors. Break out your handy multimeter, read ohms between each pair. The wire that is has nearly equal readings to the others is your CT. "Nearly" because seldom is the CT perfectly at the center of the primary winding.

[chuckb]

thanks leo, i did the check and it's B+ is the white wire. i need a 10H 65ma choke so what size of a power resistor would i need in place of the choke for now?

[Leo_Gnardo]

thanks leo, i did the check and it's B+ is the white wire. i need a 10H 65ma choke so what size of a power resistor would i need in place of the choke for now?

Hard to say. Both would serve as filter elements. If you install a resistor that simply knocks down the B+ to the same level a choke would, you'll find a good deal of hum still left on that line. OTOH if you put in a resistor large enough to knock down the hum to the level you'd expect from the choke, then you have to accept the large loss of high voltage to the screen grids, and if it's in series with the rest of the hi voltage circuit, lower hi voltage to the rest of the circuit.

For a value just to prove the amp's working, say anywhere from 100 to 500 ohms for a "proof of performance" test. And make that a 10W Resistor.

[loudthud]

Peavey likes to use a 400 Ohm 10W. That's not a standard value, 390 is close enough. They run quite hot so mount them up in the air off any PCB or eyelet board.

[Enzo]

Peavey has used 400 ohms forever. And in fact when you order one from them, sometimes you get a 390 instead, due to supply issues.

[Dave H]

what size of a power resistor would i need in place of the choke for now?

The 1974 uses 1k5 doesn't it? I have 1k 5W in mine.