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Old 24th December 2008, 10:51 PM   #1
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Default McIntosh transformer turns ratio

I was studying the MC275 schematic and was wondering what the turns ratio is for that output transformer.

I searched and found another thread where Douglas (Bandersnatch) said that it is 8:1 to the 8 ohm tap. I'm guessing that this is the ratio of turns on one of the primaries to the 8 ohm secondary (three total primaries). Since the output tubes work into two of the primaries, as far as the output tubes are concerned the turns ratio is 16:1.

Is this correct? Anyone know anything about these transformer specs?
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Old 25th December 2008, 12:50 AM   #2
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The three primary windings on this transformer are 600 ohms each, end to end. IE: Plate to plate = 600 ohms; cathode to cathode = 600 ohms; driver plate to driver plate = 600 ohms.
The MC60, MC75 are 600 ohms. The MC30 and MC40 are 1000 ohms.
Hope this helps...
Daniel
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Old 26th December 2008, 12:15 AM   #3
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Thanks, Daniel.

I was looking at the Plitron unity coupled transformer and the turns ratio seemed a bit high (over 28:1 ratio for all primaries to the secondary). If the Mac transformer is exactly 600 ohms this would be a turns ratio of about 8.6:1 per primary winding or a little over 17:1 for the entire output tube load, since it uses two windings to load the power tubes.

Have I got all this right?

It seems that the primary impedance of the Plitron is quite a bit higher at about 1600 ohms for the plate to plate winding with an 8 ohm load. It seems to me at first glance that you wouldn't get nearly as much power out with the Plitron transformer.

Any thoughts?
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Old 26th December 2008, 04:44 AM   #4
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Download a copy of the Radiotron Designer's Handbook. It covers the McIntosh output transformer design.

If you split a standard output transformer between the plate and cathode, you've changed the turns ratio by splitting the primary that way (4 not 2 sections). If you work the turns vs. impedance equation then, it all makes very simple sense!

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Old 26th December 2008, 05:20 AM   #5
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As far as I can tell, Plitron is spec'ing that high 28:1 ratio for a 4k primary impedance, which is the equivalent load seen by the tubes, given a 5 ohm secondary impedance. The actual windings are 1k, like the MC30, but for a strange 5 ohm secondary. I'd hope that they could make a standard 4/8 ohm winding instead. Nice transformer, but the price is way out of my league.
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Old 26th December 2008, 08:59 PM   #6
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Unfortunately, when you load the 1070UC with 8 ohms you get almost a 6400 ohm primary impedance, which just throws away power in my opinion.

I emailed Plitron and they said that they could alter the design if I agree to buy in quantity. Not likely!
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Old 26th December 2008, 10:19 PM   #7
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Quote:
Originally posted by SpreadSpectrum
Unfortunately, when you load the 1070UC with 8 ohms you get almost a 6400 ohm primary impedance, which just throws away power in my opinion.

I emailed Plitron and they said that they could alter the design if I agree to buy in quantity. Not likely!
Quantity!?!? That's disappointing ... I'd love to buy a pair (if I had $700 to spare), but 5R output is just too useless.


If this is for your own project and not any sort of business endeavor, email me regarding another possible option
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Old 27th December 2008, 04:14 PM   #8
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jon,

I am curious as to what your other option is. You don't seem to have the email button enabled.

I am just interested for personal experimentation.

Heath
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Old 27th December 2008, 09:50 PM   #9
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Oops, my bad... message sent
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