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Old 31st December 2008, 10:02 AM   #1
Skorpio is offline Skorpio  Denmark
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Default Simple EL84 amp...

Has anybody tried this circuit:

http://diyparadise.com/web/index.php...d=135&Itemid=5

I have not seen this on any tubeamp yet, what are the pros and cons?

Happy new year!
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Old 31st December 2008, 03:06 PM   #2
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One of the cons is that with the output stage as phase splitter, you limit yourself to about 1/2 the power you get with a "normal" phase splitter.

There is a discussion of this circuit elsewhere on the forum, precipitating from a magazine article reproduced on someone's site (IIRC one of the US tube or transformer sippliers)

dave
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Old 2nd January 2009, 08:27 AM   #3
Skorpio is offline Skorpio  Denmark
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This gyy measures 10W output with 0.6% distorsion....I don't think it is half of normal.....it is like the Baby Huey?

Can't seem to find that discussion?
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Old 2nd January 2009, 10:46 AM   #4
mjf is offline mjf  Austria
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i think it is a push-pull design that runs in class a (most of the time) .10w output should be able.
greetings.........
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Old 2nd January 2009, 04:32 PM   #5
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Quote:
Originally posted by Skorpio
This gyy measures 10W output with 0.6% distorsion....I don't think it is half of normal.....it is like the Baby Huey?
Bruce followed the idea of that amp in his EL84 Push-Pull tube amp build. He did a number of measurements and was getting less than 0.7% at 10W.

I would like to see that discussion also.
Cheers
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Old 2nd January 2009, 07:14 PM   #6
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I don't see it as hobbled to 1/2 whatever normal class A
power output would have been... Certainly it needs twice
the drive signal voltage swing to achieve the same output.
No big deal, that swing is still only a small fraction of B+.

These sort self splitters are limited to class A operations.
Once the driven side cuts off, it can't pass any information
to the cathode of the opposing device to fill in the other
half of the waveform. Class AB simply ain't gonna work.

A2 is also right out. Bleeds grid current pollution onto the
shared cathode node that make it impossible to split the
music signal with accuracy.

But as long as Class A is all you care about, I don't think
this circuit any less powerful than "normal". Should have
characteristic distortion half single Ended, half PushPull.
Its never going to be in perfect cancellation of the 2nd
harmonic, which is fine by me.

Antitriode is a slightly more evolved scheme that might
be worth looking into. If you like this sort of thing....
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Old 2nd January 2009, 07:40 PM   #7
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Quote:
Originally posted by kenpeter
These sort self splitters are limited to class A operations.
I haven't seen it explained quite as well (at least that sunk into my head). So due to Class A about half the power possible vrs Class AB.

Here are the other threads i was mentioning earlier.

Very simple P-P output stage...will it work?
modifications to compact EL84 amp

You might also want to search on Audio Asylum for John Swenson's variation

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Old 2nd January 2009, 09:25 PM   #8
mjf is offline mjf  Austria
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Default class ab

i think heatdisspation is often the limitation to class a outputpower;
in push-pull-designs(ab and a) there is nearly no limitation of the outputcurrent(equal outputpower?),but in single ended there is it i think .................
regards............
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Old 3rd January 2009, 06:44 AM   #9
Ian444 is offline Ian444  Australia
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Skorpio, I tried Bruce's implementation of the output section on a Chinese 6L6GC push-pull amp and it immediately sounded better, wider frequency range and more clarity. Maybe the CCS helps too. Then I drove it straight from the output of the first input valve (6N2 with both halves in parallel) instead of from one half of the LTP phase splitter, this gave more detail from the music. So now I have 2 x 6N1's just sitting there, heaters glowing but no power on the plates...

So as long as you use the CCS and don't mind class A operation only, I think its a great circuit and doesn't seem to compromise sound quality at all, in my case it was a definite improvement. Less components and better sound...

Thanks for the class A explanation kenpeter, easy to understand.
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Old 3rd January 2009, 07:32 AM   #10
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Easy to understand??? Never been accused of that before! Must be slipping...
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