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Old 17th April 2012, 06:45 PM   #1
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Default 6-8x el84 Per channel

Looking for a schematic with 6-8 EL84s PP per channel, Preferably 8 Something like :: AUDIOVALVE :: unique highend tube amplifier made in germany .. , Have been looking on google but can only seem to find designs with 2-4 tubes. So do you know any designs like this or do you have the schematic for the avalon ?

(This is for a school project)
Regards x3me00/viktor
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Old 17th April 2012, 07:07 PM   #2
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Choose any circuit, including such for a 2 tubes, and multiply currents by the quantity you want, and divide the output impedance from the transformer for a same amount. Finally, add some low value resistors (10R) between plates, screens, and grids. And if you will use cathode bias, divide the ohmic value for them by the amount, and the power increased similarly. If they are operated without grid positive current, the driver no need modifications at all, nor the NFB if it exists.
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Old 17th April 2012, 07:27 PM   #3
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Allright, Thanks for a very informative answer. Will do something like that on paper once i find a design to use and then post it .

Regards x3me00/viktor
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Old 17th April 2012, 09:29 PM   #4
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2 X EL84 almost equivalent to EL34. If you need more power than a pair of EL84 can deliver, pair of EL34 usually is the way to go, unless you have size restrictions.
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Old 18th April 2012, 03:40 AM   #5
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What's cool about EL84's is that they are so easy to drive, even compared to EL34's. A push-pull-parallel EL84 amp could make 25 watts per channel and only require 11 volts peak to the EL84 grids to get there. Come to think of it, SY's ImPasse would make a good driver for that... No?
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Old 18th April 2012, 04:39 AM   #6
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It is very good idea. Except EL84 tubes have to be carefully selected to match each other on all swing of signal.
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Old 18th April 2012, 12:36 PM   #7
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Quote:
Originally Posted by DeathRex View Post
2 X EL84 almost equivalent to EL34. If you need more power than a pair of EL84 can deliver, pair of EL34 usually is the way to go, unless you have size restrictions.
I believe that 2 * 2 * EL84 needs more load impedance than 2 * EL34. EL34 needs about 3K and single push pull el84 needs about 11K, so 2 pairs need about 5-6Kohm for proper working. Im remembering, so I may be wrong.
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Old 18th April 2012, 01:16 PM   #8
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Quote:
A push-pull-parallel EL84 amp could make 25 watts per channel......single push pull el84 needs about 11K, so 2 pairs need about 5-6Kohm for proper working
I make a board using EL84's called the Simple P-P. It uses a 6600 to 8000 ohm load for 15 to 25 WPC from a pair of tubes. To get 25 WPC you need good tubes and a B+ that is over spec. I have used NOS Sylvania 6BQ5 or JJ EL84 at 430 volts plate and 320 screen for 30 WPC with a 6600 ohm load.

I simply wired two channels in parallel through a common OPT for 60 WPC from 4 JJ EL84's with a 3300 ohm load and 430 volts B+.

Don't try this with wimpy tubes!

Quote:
It is very good idea. Except EL84 tubes have to be carefully selected to match each other on all swing of signal.
Tube matching is a good idea for any design where multiple tubes are paralleled, and usually required unless individual bias adjustments are used.
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Old 18th April 2012, 01:18 PM   #9
lechuck is offline lechuck  Netherlands
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Quote:
Originally Posted by Osvaldo de Banfield View Post
I believe that 2 * 2 * EL84 needs more load impedance than 2 * EL34. EL34 needs about 3K and single push pull el84 needs about 11K, so 2 pairs need about 5-6Kohm for proper working. Im remembering, so I may be wrong.
I have been using a pair of EL84's in PP UL config on 8k pri. without any problems, a PPP config should be able to work nicely with 4k pri.

@TS:
Do you already have transformers for your project? If so, could you post the specifications of these transformers?
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Old 18th April 2012, 02:35 PM   #10
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Quote:
Originally Posted by tubelab.com View Post
..... To get 25 WPC you need good tubes and a B+ that is over spec. I have used NOS Sylvania 6BQ5 or JJ EL84 at 430 volts plate and 320 screen for 30 WPC with a 6600 ohm load.
Wow... 430v plate... no fireworks? The mil-spec Sovtek EL84M should be more reliable at that kind of voltage...
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