Fairchild 275 Pair on Auction site

I have a pair of N.O.S g.e.c kt77's that I one day want to do the 260 mod too but I still need another pair to go forth with. Until then I'm happily lisiteng to them with a original pair of Svetlana winged c 6l6gc's.
 
Your better off comparing it to a amp that uses the same output tube compliment which has already been said. If you want to use the marantz's that you listed try those are more on par with the output power and tubes that they use.
Fairchild amps are a good example as as all of them used either 1614/(6l6gc) el34/6ca7 except the 275 but they didn't all start out using that tube compliment and changed it up from the 255 to 260.
When the Fairchild 255 came out it used a pair of 6l6 for tubes and power was rated at 25w. Then the 255a came out and the power increased to 30w using a pair of 6ca7's. The 260 originally used a pair of 1614 metal output tubes which are basically a 6l6 on steroids. The tube was mostly used in rf applications and allowed them to get the '50w claimed output. They then came out with a modification called the 260r revision which then allowed you to use 6ca7 /el34 tubes.
There were a number of post-Williamson amps that used the big 6550 /KT88 outputs, the Dynaco Mk-3 probably the most numerous. I mentioned the Marantz Mullards because they were a touchstone standard in that era.
Fwiw, some owners of multiple examples think the MC225 the best sounding McIntosh tube amp, and the Marantz 8/ 8B the alternative. The 225 is afaik the simplest McIntosh amp using the unity coupled output circuit.
 
Fairchild used double C-core grain-oriented output transformers. Winding them had to be an absolute pain in the keister. I'm not sure that even McIntosh went quite so far out in their OPT designs. I'd love to see someone reproduce the Fairchild OPTs, but the cost would probably be prohibitive.
 
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Fairchild used double C-core grain-oriented output transformers. Winding them had to be an absolute pain in the keister. I'm not sure that even McIntosh went quite so far out in their OPT designs. I'd love to see someone reproduce the Fairchild OPTs, but the cost would probably be prohibitive.
Afaik, Todd made the OPTs for Fairchild.
 
Indeed. This image was taken from an article in the November 1956 Radio & Television News. Note the transformer wound through a pair of C cores, rather than the single C core of that Macintosh 240 OPT. Also, note the byline.
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I've seen similar construction in German xformers, single sided. I recall other examples of both constructions and am not aware of the practical advantages.
How were the UTC LS series done?
 
What are the advantages of the double C-core?

I sort-of understand eliminating the switching transients with McIntoshs' 1947 development of the "unity coupled" transformers... But how does the Fairchild/Todd transformer keep thd below 1% at 75% of rated power? I think, (If I'm not mistaken) that the Mac Trannies of the same time period have quieter numbers, but I admit that the specs are very close in the lions share of the curve.

I've read this ( http://www.vt4c.com/teach_room/choose_transformer.html ) and my tiny mind is having a hard time understand the advantages of the double C... It is obviously twice the manufacturing time... is it Magnetics, harmonics, or just a cleaner amplification method?

I also found this video where Gordon Gow is explaining the Unity Coupling on the Mac Tranny-
 
It would be interesting to see some side-by-side evaluations. Obviously the guys at Fairchild and Todd thought it was worth the extra expense for an all-out amplifier.
 
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