18 Watt OT

[FunkyE9th]

I was just at Magnetic Components site checking out their 18Watt OT. Thinking of experimenting with it. It says they use M6 steel. Is M6 the standard steel for the original Marshall OTs? What's also interesting, the primary is as follows...

PRIMARY IMPEDANCE = 10.8K Ω WITH 4Ω LOAD
PRIMARY IMPEDANCE = 9.2K Ω WITH 8Ω LOAD
PRIMARY IMPEDANCE = 8.4K Ω WITH 16Ω LOAD

Any opinions/comments?

Thanks!

[Phil_S]

The primary:secondary is generally about the turns ratio. I think, what they are saying is that the typical tapping points for 8 and 16 ohms are not where makers usually put them to keep the primary at the same impedance.

I am guessing that "someone" "figured out" what "sounds best" with respect to the turns ratios and EL84's. But that's just a guess and a cynical guess, at that.

[JamesHealey]

It's a clone of the original RS Spares transformer used on the original 18w Marshalls from the VERY early 60s.

It's essentially a hifi transformer, that was available as a replacement for "many" applications that Marshall used on there amps.


so it had a few different primary impedances available for different tube types etc.

the 8.4k would be the perfect load for two EL84 tubes in A/B Push Pull.

[FunkyE9th]

Thanks. That's what I was trying to understand. I was wondering if it was a clone, or if the spec was their own take on the OT.