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Old 5th January 2011, 01:58 PM   #1001
Tyimo is offline Tyimo  Hungary
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Default Power tansformer

Hi!
How big power transformer need for such an EL84 PP amplifier?
Is 100VA enough for two channels?

Tyimo
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Old 5th January 2011, 09:15 PM   #1002
Tyimo is offline Tyimo  Hungary
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Nobody knows the VA rating of the power transformer for this amp????
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Old 6th January 2011, 04:25 AM   #1003
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My BH monoblocks are each powered by Hammond 270EX transformers 275-0-275 @ 125ma each; the Hammond website now rates the 270EX at 144ma or 118VA.

The EL84's need about 38ma each x 4, plus the phase splitter current, etc. so a stereo amp needs 175-200ma or so....more than 100VA

Last edited by boywonder; 6th January 2011 at 04:36 AM.
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Old 6th January 2011, 11:26 AM   #1004
Tyimo is offline Tyimo  Hungary
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Thanks!
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Old 24th February 2011, 05:00 PM   #1005
CSlee is offline CSlee  United Kingdom
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I visited my old dear at the weekend and had a look at her BH.

Couple of points, the bias for the input stage seems to drift every time I visit. Reading the plates of the input valves it always drifts a few volts. What might be the reason for this? Or is that quite normal?

Also, a more generic question. The volume pot becomes noisy from 50%-99% turned, becoming more and more noisy. Then at its fully on position it is dead silent. Is this poor layout or wiring? Would a stepped attenuator be the answer?

The sound still amazes me, can't believe I gave it to her!

Cheers

Charlie
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Old 24th February 2011, 05:30 PM   #1006
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Quote:
Originally Posted by CSlee View Post
Couple of points, the bias for the input stage seems to drift every time I visit. Reading the plates of the input valves it always drifts a few volts. What might be the reason for this? Or is that quite normal?
Yes, that's quite normal; I've seen the same thing in my own projects. As to what causes it, it's due to fluxuations in the AC mains voltage. The bias current of the finals drifts a few mA, depending on the time of day, and the overall load on the AC distribution system.

Quote:
Also, a more generic question. The volume pot becomes noisy from 50%-99% turned, becoming more and more noisy. Then at its fully on position it is dead silent. Is this poor layout or wiring? Would a stepped attenuator be the answer?

The sound still amazes me, can't believe I gave it to her! :headbash
It's dirt on the track and/or the thing is simply worn out. You might also want to take a look at the schemo to see if there is any DC flowing across the track and wiper. That'll cause a pot, especially a high resistance one, to go scratchy in no time.
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Old 27th February 2011, 07:08 PM   #1007
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Default Schematic for the latest version? & Parts list ?

Has Ginger settled on this version? A finalized schematic is would be great. This amp fits my requirments nicely.... Excellent project/thread... Thx
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Old 28th February 2011, 11:18 AM   #1008
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+1 On that request
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Old 28th February 2011, 11:21 AM   #1009
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Has Ginger settled on this version?
What version do you call "this version"?
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Old 28th February 2011, 12:12 PM   #1010
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There are "essentially" 2 versions.

From the Wiki page I've put up:
"AFAIK there are 2 major versions. The first (auto bias), which is probably the one newbies should build and a fixed bias version."

Baby Huey PP EL84 amplifier - diyAudio

I would suggest building the version in the Wiki (Which is AFAIK the latest auto bias version). And you can always try something you've lifted from this thread.
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