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Old 29th November 2004, 05:35 PM   #1
arbus is offline arbus  Taiwan
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Smile Having a problem with building this 6C45 PP amp.

Hi .
I want to try this schem.
http://digilander.libero.it/paeng/devices_frame.htm
Is there any suggestion about the input trans like the SOT3?
http://digilander.libero.it/paeng/magnetics_frame.htm
I have two old UTC A20 like this.
Application: Mixing, matching
Primary lmp Ohms 50,125/150,200/250,333,500/600
Secondary lmp Ohms 50,125/150,200/250,333,500/600
Can I use them in this case?
If its OK how should I choice the primary and secondary lmp?
My English is poor, forgive me plz.
Any response will be very useful to me. Thanks a lot.
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Old 30th November 2004, 03:54 PM   #2
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Hi Arbus,

The input transformer SOT3 that Stefano uses is a phase splitting transformer and therefore has two matched secondary windings that can be connected (internally or externally) in anti-phase yielding the two antiphase signals necessary to drive the push-pull output stage.

The UTC A20, judging from the photo and your data, has only one secondary winding and therefore cannot be used for phase splitting.

ciao

James
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Old 30th November 2004, 08:48 PM   #3
arbus is offline arbus  Taiwan
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Thank you Tames.
And what do you think about how much static resistance of the primary and the secondary will be better in this case?
Or just take any transformer that i can find it's data sheet as the example.
Thanks again.
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Old 30th November 2004, 09:06 PM   #4
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Your transformers should work. Both windings are center tapped. Perfect for PP duty.
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Old 30th November 2004, 09:07 PM   #5
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In general for an input transformer use a 1:1 connection at the highest impedance possible - so 600:600 in this case. However if your source impedance is high it may have trouble driving the input side at l.f. and trouble driving the reflected capacitance of the 6C45 at h.f. In other words they are not great transformers for this application. They might work well so trying them is the only way to be sure.

Thinking about the PP use, if you use both in parallel connection at input and with each secondary driving a seperate 6C45 but with one secondary reversed connected then one would approximate the phase splitting required for PP. The balance would not be that good and the frequency response might not be great but it should work enough to see if you like the sound of 6C45 in PP...

have fun!

James
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Old 30th November 2004, 09:10 PM   #6
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Frank,

Did I miss the CT info? |Do you know these trannies? I don't so I may well have it wrong.

However one still needs a low source inpedance to drive the 6C45s through the trannie...

ciao

James
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Old 1st December 2004, 07:55 AM   #7
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James,

I have used these transformers ... Many years ago.
They are good quality transformers and quite heavy for their size.
If you wire the primary for 50 ohms and the secondary for 300/CT/300 ohms, you'll get voltage gain. It might be enough to drive the PP grids.

I'd try the transformers and see how they work.
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Old 2nd December 2004, 06:08 AM   #8
arbus is offline arbus  Taiwan
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Thumbs up Thanks Frank and James.

Now I see. I'll try it.
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Old 3rd December 2004, 11:02 AM   #9
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Frank,

Thanks for the update on the trannies.

Arbus,

Good luck with the project. I've used 6C45 qute a lot as drivers and output tubes. It's a nice tube but needs some tweaking to tame oscillations and can need a lot of driving as it has a lot of Millar capacitance. My latest creations uses it as the lower valve of a cascode to minimise the Millar cap. Let us know how you get on.

ciao

James
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