Question regarding Magnequest transformers

JohnEss · 2101

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Offline JohnEss

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on: September 12, 2023, 12:37:12 AM
A friend gifted me a pair of the Magnequest transformers from an older SEX kit and I was wondering if anyone here has the specs and correct wiring diagram for these. Writing on the outside says "CUSTOM PART NO 05009"...Thanks in advance.



Offline Paul Joppa

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Reply #1 on: September 12, 2023, 04:35:38 AM
I'll dig out my notes - and get back to you shortly.

Paul Joppa


Offline Paul Joppa

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Reply #2 on: September 12, 2023, 06:09:57 AM
OK, found my notes. The transformer is the BH-1, our first custom/proprietary Magnequest product. Spec is 8000:8 ohms. The core is M4, a higher grade of grain-oriented silicon steel than the usual M6. A few were made with nickel pinstripes. This is a parallel-feed (parafeed) output, so no DC current - it was used with the PC-2 plate choke which is a Magnequest BCP-15 modified with a smaller air gap for more inductance (50 henries at 40mADC).

I can't find any documentation of the lead colors, but my personal SEX amp has the upgrade installed. So I took  down to the lab and found the standard colors were used - primary winding blue to plate, red to AC ground; secondary orange is positive to speaker, black is ground.

Paul Joppa


Offline JohnEss

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Reply #3 on: September 19, 2023, 07:00:33 AM
Thanks for looking that up.



Offline ssssly

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Reply #4 on: November 04, 2023, 05:33:22 AM
 I just started rebuilding my old SEX amps with MQ iron as well. The old 2.0 instructions are still available on the way back machine

https://web.archive.org/web/20060312101926/http://www.bottlehead.com/et/adobespc/S.E.X./ironsupplementkit.htm

That has the old C4S boards with the twin 270k resistors though. If I remember correctly without looking at my notes the resistors should be ~150k 2w (R1) 500r 1/2w (R2) for the newer boards.

And the parts layout changed post 2.1. So depending on the instructions version you have for them, you may need to adjust terminal numbers.
« Last Edit: November 04, 2023, 05:48:48 AM by ssssly »