Need help finding replacement output transformer

[jazbo8]

Classictone makes this one for the JTM45/100 that is 4k primary input.
100W Marshall JTM45/100 Output Transformer, 1202-84
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Here is the load line if the existing operating conditions are used, the output power is around 120W, wonder why the original OPT blew up?

Eg1 is changed to -31V to set the bias at 40mA, due to the slight difference in the tube model:

[Alan0354]

You need to divide the 8.14k by two, since there are two pairs of 6L6s. In any case, finding a direct replacement OPT would be very hard, unless you want to pay for a custom wound one. The other alternative is to modify the operating conditions, so an off-the-shelf OPT can be used. In this case, by dropping the plate and screen voltages a bit, the Hammond 165R (5k, 100W) could work. Here is one such load line example (a single pair, one side shown only):

[ATTACH=CONFIG]29870[/ATTACH]

Yes I forgot it's two pair. That should make things a lot easier. If the load is 8 ohm, then even the OT for twin can be used.(2K:4ohm). With 8 ohm load, you get 4K primary.

For 4K primary, it should be a lot easier to find.


But the other question is.....No body worry about the 650V?

[jazbo8]

No body worry about the 650V?

It's actually worse, during the flyback, the primary winding could see well over 1KV, so the isolation could have broken down and caused arcing inside the OPT. And this is another good reason to use a lower B+ when replacing the OPT.

[Alan0354]

It's actually worse, during the flyback, the primary winding could see well over 1KV, so the isolation could have broken down and caused arcing inside the OPT. And this is another good reason to use a lower B+ when replacing the OPT.

That's what I was worry all along right from the beginning. OP doesn't seems to worry at all. I don't think I can agree. You really need actually open that particular transformer to know how good is the insulation. As in post #7, it really depends on how the primary is wound. I calculated with tube saturation at 100V, you have 1150V peak on the primary or the output if you use 650V.