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24th December 2008, 10:51 PM  #1 
diyAudio Member
Join Date: Nov 2007

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? 
25th December 2008, 12:50 AM  #2 
diyAudio Member
Join Date: May 2005
Location: California

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 
26th December 2008, 12:15 AM  #3 
diyAudio Member
Join Date: Nov 2007

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? 
26th December 2008, 04:44 AM  #4 
expert in tautology
diyAudio Member

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! __bear
__________________
__bear http://www.bearlabs.com  Btw, I don't actually know anything, FYI  every once in a while I say something that makes sense... ] 
26th December 2008, 05:20 AM  #5 
diyAudio Member
Join Date: Nov 2005

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.

26th December 2008, 08:59 PM  #6 
diyAudio Member
Join Date: Nov 2007

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! 
26th December 2008, 10:19 PM  #7  
diyAudio Member
Join Date: Nov 2005

Quote:
If this is for your own project and not any sort of business endeavor, email me regarding another possible option 

27th December 2008, 04:14 PM  #8 
diyAudio Member
Join Date: Nov 2007

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 
27th December 2008, 09:50 PM  #9 
diyAudio Member
Join Date: Nov 2005

Oops, my bad... message sent

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