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Old 8th April 2005, 07:11 PM   #1
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Default anyone tried the diy paradise simple el84 pp

I too, just picked up an old Magnavox console stereo PP amp with EL84s and 6EU7s. Haven't powered it up yet but was told it worked perfectly. I'm not sure what to do with it yet and was wondering if it is worth keeping it in its original configuration or should I do something else with it? How good are the OPT? Not the best but are they pretty good?

This diyParadise Simple EL84 PP amp looks interesting and was wondering if anyone has tried it yet. How does it sound? Are there any other PP circuits that are worth building with these EL84s?

http://www.diyparadise.com/buildel84b.html

Also on my plate is the RH EL84 partial feedback SE amp now that I have some EL84 to use... Too little time but need to start building....
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Old 8th April 2005, 07:27 PM   #2
SY is offline SY  United States
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We just had a thread about this, or at least another variant on that circuit. It's not that simple (you need a high current CCS), it does not overload gracefully, and the distortion is high.
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Old 8th April 2005, 08:23 PM   #3
Sheldon is offline Sheldon  United States
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Here's some:

http://www.wdehaan.demon.nl/mono/mono/el84dc.html
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Old 10th April 2005, 03:16 AM   #4
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http://www.wdehaan.demon.nl/mono/mono/el84dc.html

Would a normal PP OPT work with these circuits or do I need to get these multi tap OPT? Also, there is no mention on how these designs sounds. Any idea? It does look interesting though. I do like the sound of DC coupled circuits and might try one for the fun of it.

Any more circuits to try?
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Old 10th April 2005, 04:34 AM   #5
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Quote:
Originally posted by RockysDad
[url]Would a normal PP OPT work with these circuits or do I need to get these multi tap OPT?

Also, there is no mention on how these designs sounds. Any idea?

Any more circuits to try?
It sounds like you have no ultralinear taps so you must choose between running the EL84 as a triode or a pentode, but you do not need to buy new OPT's.

There are TONS of EL84 designs out there. May I be so bold as to suggest a search here and on Google?

Here's a start:

http://www.bonavolta.ch/hobby/en/audio/el84.htm
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Old 11th April 2005, 12:47 AM   #6
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Default I found one...

Since it is a Magnavox console amp that I have with the exact tubes, why not build this?

http://members.tripod.com/~gabevee/maggie.html

I'm pretty excited!!! Can't wait to start rebuilding!
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Old 11th April 2005, 04:19 AM   #7
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Default EL84 Amp

I built the Morgan Jones 'Bevois Valley" EL84 Ultralinear Push Pull. Get hold of the Morgan Jones "Valve Amplifiers" 3rd edition book. I used solid state rectifiers with 220uF main filter cap (common to both channels) plus an additional 100uF+0.47nF Polyproylene cap connected at each O/P Tranny Centretap fed via individual 100 Ohm resistors from the common supply.

I found that the grid stopper resistors on the ECC88 need to be increased from the 330R value (I used 1K8 I think). I run 5dB ONLY of global feedback - This was tuned by ear to give me the best balance of imaging and damping. The 270R output tube cathode resistors were replaced by "ring of 2" solid state current sources and I used 470uF/50V Blackgate bypass capacitors. The other thing which gave major sonic inprovements was replacement of the 1N4007 diodes in the power supply with Ultrafast diodes. Oh and I did'nt need the 68pF additional caps across the output tube grid resistors.

All tubes ECC88s and EL84s are JJ Tesla. I tried NOS 6BQ5 and Sovtek EL84 before settling on the JJs. I also tried some NOS 6DJ8 (Brimar) but found some of them were so microphonic as to be unusable even though they tested well on the valve tester.

I'm extremely happy with the result.
Cheers,
Ian
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