McIntosh transformer turns ratio

SpreadSpectrum · 24th December 2008, 10:51 PM

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?

danFrank · 25th December 2008, 12:50 AM

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

SpreadSpectrum · 26th December 2008, 12:15 AM

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?

bear · 26th December 2008, 04:44 AM

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

jon_010101 · 26th December 2008, 05:20 AM

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.

SpreadSpectrum · 26th December 2008, 08:59 PM

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!

jon_010101 · 26th December 2008, 10:19 PM

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

SpreadSpectrum · 27th December 2008, 04:14 PM

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

jon_010101 · 27th December 2008, 09:50 PM

Oops, my bad... message sent

24th December 2008, 10:51 PM	#1
SpreadSpectrum 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?

26th December 2008, 04:44 AM	#4
bear expert in tautology diyAudio Member Join Date: Apr 2002 Location: New York State USA	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 [...2SJ74 Toshiba bogus asian parts - beware! ] -- Btw, I don't actually know anything, FYI --

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25th December 2008, 12:50 AM	#2
danFrank 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
SpreadSpectrum 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, 05:20 AM	#5
jon_010101 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
SpreadSpectrum 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!

27th December 2008, 04:14 PM	#8
SpreadSpectrum 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
jon_010101 diyAudio Member Join Date: Nov 2005	Oops, my bad... message sent