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Old 11th December 2012, 12:06 PM   #1
Tesla88 is offline Tesla88  Italy
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Default EL34 PushPull UL Amp

Hi !I'm new on this forum ,i'm from Italy so sorry for any mistake.

I bought a new pair transformers for a PushPull Amp with Ultra Linear connections .
Here you find specs fot the trasformers:
TU052

Primary Z :4300 ohm
Primary Rdc :220 ohm
Primary Inductance :40H
Current :120mA
Pout rated 35W RMS

I think 4300 would be Ok for a Pair of 6CA7 - EL34 tubes in Push Pull , the UL connections are at 43%

What circuit would you suggest for best results?
What about Dynaco ST70? Any better ?
Thanks
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Old 11th December 2012, 12:19 PM   #2
DF96 is offline DF96  England
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Mullard 5-20? The main snag with that is that it has too much gain for modern sources. The Lundahl site has a modified version.
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Old 11th December 2012, 12:59 PM   #3
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Check the various board options at Classic Valve Design - Welcome!. I've always found them easy to deal with, and the products are good.
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Old 11th December 2012, 02:01 PM   #4
Tesla88 is offline Tesla88  Italy
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uhm , in the Mullard 5-20 schematic i don't like the ECC83 as driver so much ...
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Old 11th December 2012, 03:40 PM   #5
DF96 is offline DF96  England
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People often say that. Often because they have heard someone else say it. If you substitute a lower mu valve then you will need to add a CCS tail to the LTP, or use different anode resistor values to restore balance.
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Old 11th December 2012, 04:23 PM   #6
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Dynaco ST70 is a good circuit.
I would modify it by adding both bias- and drive balance adjustments.
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Old 11th December 2012, 05:09 PM   #7
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Quote:
Originally Posted by Tesla88 View Post
uhm , in the Mullard 5-20 schematic i don't like the ECC83 as driver so much ...
Check out the OPUS 5.0 A Modern Mullard thread as a reference.

jeff
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Old 12th December 2012, 12:25 AM   #8
roline is offline roline  United States
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IF you want to use less feedback the 6550 and kt88 tubes can drive the 4.3k Ra outputs easier. The 6L6, EL34 and 6P3S-E needed more feedback. There are thousands of ST70's with the EL34's if you want to copy that feedback scheme.
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Old 12th December 2012, 12:47 AM   #9
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Check the various board options at Classic Valve Design - Welcome!. I've always found them easy to deal with, and the products are good.
I've been living with the proto of Gregg-the-Geeks DynaMutt and can highly recommend it.

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Old 12th December 2012, 02:01 AM   #10
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Has anybody paid attention to the fact that the O/P trafos lack the magnetic headroom needed to cope with a GNFB induced low freq. error correction signal?

I suggest the OP scan the archives for Bandersnatch's "exolinear" style circuitry, which does not place the O/P trafo inside a NFB loop. FWIW, I like having the O/P "iron" inside a NFB loop, but what has already been acquired will not support that type of circuitry.
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