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 Post subject: GU-50 push-pull amp
PostPosted: Thu Mar 17, 2011 7:24 am 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
After completing one of the GU-50 SE amp, will probably embark on a PP amp before going for another SE amp with that tube. Any good suggestions for a simple P-P amp? Will most likely use some power transformers as the OPT. Any thoughts?


 
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 Post subject: Re: GU-50 push-pull amp
PostPosted: Thu Mar 17, 2011 8:49 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7317
Location: Pleasant Hill, California
For GU-50 push-pull you will need something like 8K 100W, the most optimal option is Edcor, $100 a piece.
We are going to start manufacturing of output transformers in Israel using amorphous cores, but I am afraid we can't make in Edcor price range.

Speaking of schematic, you can take Pyramid-VII-M bones. It's real High-End.


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 Post subject: Re: GU-50 push-pull amp
PostPosted: Thu Mar 17, 2011 1:09 pm 
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Joined: Wed Oct 01, 2008 9:14 am
Posts: 41
Location: Denmark
One thing I have always been wondering is how a standard 2x 115V <-> 6V mains transformer might do as a PP output device? If you connect an 8 ohm load to the 6V secondary, then you have something like a 6K load impedance across the dual primaries. Might be worth considering?

Coincidentally I am considering building a 'junk box' amp of whatever scrap I have floating around. Won't be anything spectacular, as I only have one output transformer worth mentioning, and it is worse than bad. Just use whatever I have at hand for the different parts, like grabbing my lonely 829B and run it in PP with my junk transformer etc.

The idea would be to have something to compare the big amp to, once that is done. Additionally I now have to wait a fair few weeks until I have my transformers, and I might spend some of that time on this side project.


 
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 Post subject: Re: GU-50 push-pull amp
PostPosted: Thu Mar 17, 2011 1:19 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7317
Location: Pleasant Hill, California
Knarf wrote:
One thing I have always been wondering is how a standard 2x 115V <-> 6V mains transformer might do as a PP output device? If you connect an 8 ohm load to the 6V secondary, then you have something like a 6K load impedance across the dual primaries. Might be worth considering?


No. They are designed for contradictory requirements A first, it has too low inductance (low end, close to saturation on 60 Hz, up to 10% loss, including on heating of core) and too high leakage inductance (high end, helps to filter out garbage due to separate bobbins). May be good though for some mid-freq amp, like security siren (300 Hz -- 3KHz), or megaphone, but it's cheaper to use some SS amp for this purpose. Wink

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А женщина даже в мужской рубашке выглядит гораздо приличнее, чем мужчина в женских колготках! Be-be-be!


 
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 Post subject: Re: GU-50 push-pull amp
PostPosted: Thu Mar 17, 2011 11:27 pm 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
If it were toroids being used? I am sure the bandwidth would be good. Smile

What would be the reflected impedances of a 115-0-115 : 18-0-18 transformer? if the 8ohm was connected across 0-18 and 18-18?


 
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 Post subject: Re: GU-50 push-pull amp
PostPosted: Fri Mar 18, 2011 12:24 am 
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Joined: Wed Oct 01, 2008 9:14 am
Posts: 41
Location: Denmark
I have heard some people claim good results from using mains toroid transformers, never done it myself. I suspect Anatoliy's comments would still apply.

8 ohm across 0-18: 8 * (115/18)^2 = 327 ohm.
8 ohm across 18-0-18: 8 * (115/36)^2 = 82 ohm.

This is per side, of course, so double this for Ra-a. Kind of low, unfortunately.


 
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 Post subject: Re: GU-50 push-pull amp
PostPosted: Fri Mar 18, 2011 5:26 am 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
that's where the beauty of the toroid comes in, add or minus windings to your heart's content Smile


 
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