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zman01 12th October 2012 06:32 PM

Cheaper OPTs and dual secondaries
I've been trying to locate some budget OPTs with dual secondaries for a friend's SSE build. The Edcor CXSE come with choice for only single secondary; out of luck with the entry level Transcendars too - no 8 and 4 Ohm secondaries before their 15 watt model.

Only Hammond has as such, but they are rated for 100 Hz - 15k Hz which is much lower than the Edcor's (40 Hz - 18 KHz).

The tubes for this project are EL34s. My friend would be swapping in and out speakers of different impedance ratings and would like to have an option of 4 & 8 Ohms.

I have also thought about a OPT with 6 Ohm secondaries as middle ground, but also read that the impedance that the tubes would see from connecting 4 or 8 Ohm speakers would not be necessarily be linear (depends on OPT design).

Would appreciate any suggestions in this regard.

tomchr 12th October 2012 06:54 PM

Jack Eliano of Electra-Print recommends using 6 ohm secondaries as a middle ground between 4 and 8 ohm. Of course, when you load a 6-ohm secondary with a 4-ohm speaker, the primary impedance will be 2/3 of the nominal primary impedance and vice versa for when loading with an 8-ohm driver. For many practical purposes, this doesn't make that much difference.

When I had E-P wind my transformers, I still went with dual secondaries, though. I have my eyes on some magnetostats that come close to 3 ohm...

Another option for you may be to look at replacement transformers for various amplifiers. Triode Electronics and AES have some.


zman01 12th October 2012 07:52 PM


Thanks a lot for the suggestions. I wanted to double check as I read in a forum that Edcor did not confirm proportionate change in primary (for that particular discussion IIRC it was an Edcor OPT with 10k primary, builder loaded the 8 Ohm secondary with a 4 Ohm speaker to get 5k primary); it was working pretty well for the builder though.

Regarding replacement transformers, lot of the more affordable stuff I see at AES and Triode are mainly for guitar amps? Sorry if that sounds stupid, but I am pretty much a noob here :).

Most likely Edcor GXSE (not CXSE as I had incorrectly mentioned in my first post) with 6 Ohm secondaries it shall be.

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