help subbing a Marshal OT

[Randall]

I have a 1986 Marshall Artist 4203 combo with a dead OT. It is a drake 292-700/6. I think the /6 is a date code. Not coming up with anything. The amp runs 2 EL34s at 4/8 ohms. Anyone know what sub I could use?

[Jon Snell]

It is a standard 40/50W EL34 transformer, nothing special.
Have you looked here; https://www.tubesandmore.com/product...ement-marshall
If a lie down type, look up DSL401 https://www.tubeampdoctor.com/en/out...for-40w-dsl401 or standup type JCM800 series https://www.tubeampdoctor.com/en/out...8-16-ohm?c=105

Hope that helps.

[Randall]

Thank you John, that is helpful.

[Jazz P Bass]

You could go with the Heyboer APD-8039H.
https://www.ebay.com/itm/284632581613

[Helmholtz]

You could go with the Heyboer APD-8039H.
https://www.ebay.com/itm/284632581613

That is an 8k OT for KT66s.

EL34s want around 3.4k.

[Chuck H]

That is an 8k OT for KT66s.

EL34s want around 3.4k.

Ah, but it has 4/8/16 taps. So it could be run at half impedance (using the 8/16 taps as 4/8 taps) making it 4k. I've never had a problem manipulating transformer specs like this within the guitar amp frequency range. In fact I've only had happy accidents that sounded good.

[Helmholtz]

So it could be run at half impedance (using the 8/16 taps as 4/8 taps) making it 4k.

I was reluctant to suggest that solution.

Reason is that compared with designated 8k operation the primary peak current will be almost doubled, which might exceed the OT's current limit at full power.

Second reason is, that an 8k OT typically has around twice the DCR of a 3.4k OT of same size, due to more turns of thinner wire.
This means doubled power loss.
So output will be lower by 5W to 10W and OT wire temperature will increase.

[Chuck H]

I was reluctant to suggest that solution.

Reason is that compared with designated 8k operation the primary peak current will be almost doubled, which might exceed the OT's current limit at full power.

Second reason is, that an 8k OT typically has around twice the DCR of a 3.4k OT of same size, due to more turns of thinner wire.
This means doubled power loss.
So output will be lower by 5W to 10W and OT wire temperature will increase.

All good reasons not to then. I'm actually aware of these parameters but have become cavalier since I never had a problem. I've done this most with Hammond 16XX off the shelf units which are nearly indestructible.