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ellejammer 6th December 2010 01:49 PM

Unknown PP output transformers
Hi everybody,

3 years ago I got on the bay a NOS pair of identical PP output transformers.
The end bells say respectively:
FT4725698-138305E and FT4725698-138217E
The core is a 1_3/4 inch stack of EI 1_1/8 inch lamination
Primary inductance is about 250H @ 5Vrms, 50Hz, plate to plate with a DC resistance of 125+125 ohm.
They weight 2.2Kg each and look like an A470, maybe a bit smaller...
Nominal impedances, from voltage ratio measurements, are:
Primary: 7.0 Kohm plate to plate
Second: 0-8-16-32 ohm, tapped

Does anybody know the manufacturer and their use ?
Thank you, Franco

Tom Bavis 6th December 2010 07:48 PM

138 is Stancor - 1963 week 5 and 1962 week 17 (1952 and 1972 seem unlikely). Harman-Kardon had part numbers that started with "FT", so that's where I would look - one of their 6L6 or 7355 based amplifiers. Like A500, A700, HK-250, TA260...

ellejammer 7th December 2010 05:56 AM

OK Tom, I thank you for the very detailed info and fast answer !
I'm going to check with Harman-Kardon....

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