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Got a version that will work with EL-84's?

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Ivan303

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In Reply to: This basic circuit works very well with KT88.6550 type tubes... posted by Allen Wright on April 2, 2007 at 10:09:30:

Have some nice pair of 8K PP OT's without UL taps and am looking for an ultimate EL-84 PP amp schematic.

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EL84 Amp - another possibility - Gingertube 18:14:21 04/04/07 (2)
This design is the best amp in my collection. Of course we all think our own design sounds the best BUT it is truely stunning. I called it the "Baby Huey".
Bas Horneman has kindly hosted the schematics on his site.
The Amp Schematic:
http://basaudio.net/schematics/pp/ppel84_baby_huey.gif
The power supply Schematic
http://basaudio.net/schematics/pp/p...by_huey_psu.gif
Recent Mods:
1)The EL84 CCS Cathode bypasses are now 1000uF/25V Blackgate NX in place of the 4700uF/470uF/1uF networks shown.
2)10 Ohm + 220nF zobel added across the 4 Ohm secondary tap (the tap I use)
3) 47 Ohm series resitors in the the HV feeds to Left and Right Channels dropped to 4R7
4) Note that there is a very small amout of global feedback and local balanced shunt feedback set by the 15K which connects across the 2 47K resistors off the EL84 Anodes.
IF - 2 Ohms Output Impedance is acceptable to you THEN ditch the global feedback altogether by removing that 12K global fedback resistor and increase that 15K to 27K - THIS is how I run my amp (I tried 33K but thought it a bit much)
IF 2 Ohms Output Impedance is not acceptable then leave the global feedback as is but increase the 15K to 20K. This was the best option with global feedback intact for an Output Impedance of just over 1 Ohm.
B.T.W. This whole design grew aout of an ECL86 (6GW8) circuit by Yves Monmagnon.
here
http://www.diyaudio.com/forums/attachment.php?s=&postid=552739&stamp=1105777406
The ECL86 version I built and subsequently sold was also seriously stunning.
Cheers,
Ian
- Re: EL84 Amp - another possibility - pipo 02:46:29 04/05/07 (1)
  http://www.artimusica.nl/wim/dc_coupled_amp.pdf
  a nice direct coupled amp.
  - Re: EL84 Amp - another possibility is the STC el84 or ecl82 - pipo 02:49:18 04/05/07 (0)
    Do a search for stc amps. Those Japs know their tube stuff
Only need to reduce the B+... - Allen Wright 01:25:01 04/04/07 (0)
...and change the cathode R's to get the running current you need.
Nothing else needs to change at all.
Except if you want to do it correctly - you must use a choke input PS - big sonic difference!
Regards, Allen
It will work with them but.... - Russ57 17:01:31 04/03/07 (5)
It might be called a case of overkill as the el84 is so easy to drive. Take a look at Poinz's "music machine". It is along the same line but more for the 6v6/el84.

Russ
- I disagree... - Allen Wright 04:43:42 04/04/07 (4)
  ...my cascode circuit is not there to drive difficult loads - it's there because it came out tops sonically after 20 years of trying most every circuit, simple and complex!
  Regards, Allen
  - I think I was misunderstood - Russ57 06:14:49 04/04/07 (3)
    Hey, I love your circuit Allen. That is why I posted it first off (which I hope you don't mind).
    All I was trying to say is it almost seemed a waste to have a driver that could swing...what....four, five?? times what an el84 needs. But hey, this is DIY land and overhead is always nice. Besides, he would have lots of room to grow (say hy69 later?? and it would darn sure be in a very very linear area driving the el84).
    But Poinz's circuit is adequate for the el84 and might be easier/cheaper for some to build. That's all:)
    
    Russ
    - He did say he wanted real killer of a El84 amp... (nt) - Allen Wright 08:13:17 04/04/07 (2)
      ... and "adequate" didn't sound like what he was after.
      But yes - thanks - I'm happy for that circuit to be known, talked about, and used. Thanks for mentioning it.
      Regards, Allen
      - cascode question for allen wright - pipo 02:44:21 04/05/07 (1)
        
        In Reply to: He did say he wanted real killer of a El84 amp... (nt) posted by Allen Wright on April 4, 2007 at 08:13:17:
        
        Allen,
        I remember to have seen in an old Glass Audio magazin a version of the hedges cascode with on top of the cascode top tube a cathode follower. Did you try that too ? The author claimed that it bettered the regular cascode.
        
        maybe saw it, never tried it. - Allen Wright 06:03:17 04/05/07 (0)
        
        In Reply to: cascode question for allen wright posted by pipo on April 5, 2007 at 02:44:21:
        
        The key to the cascode in audio IS it's high output impedance. If you then load it with a lowish value non inductive resistor, you'll get a very well defined gain and consistant output impedance across a very wide frequency range, with often very low distortion as well!
        Adding a CF would, IMO, only bring in the typical CF problems - and perhaps mess up the positives of the cascode.
        I'll keep them seperate, thanks.
        Regards, Allen

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