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Yeah..Joel...i'd love to see your 01a-01a-71a amp as

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In Reply to: as an aside for our readers... check out some of Joel's work... posted by mqracing on October 13, 2005 at 11:26:53:

well..Especially in one of those yummy schematics you have. :-)
Regards,
Bas
To infinity and beyond!!!

Follow Ups:

check this out Bas - mqracing 07:40:14 10/16/05 (3)
Hi Bas:
check this out a 300B driving a 211 driving an 845PP output stage.

i'd look at LC coupling btwn the 300 and the 211 and then look at an EXO-173PPS to phase split and couple to the 845 output stage.
interesting...
- http://avrnd.com/gnu3/?doc=bbs/gnuboard.php&bo_table=circuitbox&page=4&wr_id=391 (Open in New Window)
- Awesome..but too much powerrr for my needs ;-) - Bas Horneman 09:21:10 10/17/05 (2)
  maybe one day...just for kicks! ;-)
  Cheers,
  Bas
  To infinity and beyond!!!
  - it's the architecture that is of interest.... - mqracing 17:19:44 10/18/05 (1)
    agreed... about the power quotient... and my experience has not been wholly positive (sonically) about 211's and 845's at high plate volts...
    but... the architecture... it loans itself to scaling down and some other revisions...
    for example, I would either direct couple btwn the voltage amp and the diver tube or, alternately, use LC coupling (and, LC coupling would be LESS reactive than the IT shown). Btwn the driver tube and the output stage I would use the EXO-173PPS...
    and I would look at using the following setup... 211 to 211 to 845. 211 has a mu of 12 versus mu of 4 for 300B. And you might be able dispense with the 15095 for step up duties at the front door...
    and no need on god's green earth to run that 300B at 80 mils dc plate current... it's driving the load of a succeeding grid... use like maybe Atarashi did on his T1 amps.... a 300B running with approx 12 madc of plate current... now you can get a super duper plate choke to load the anode with... again, gaining a higher effective NON_REACTIVE (comparatively speaking) load on the anode of the 300B compared to traditional and typical IT coupling with an airgapped IT...
    Use anode chokes on top of the first two tubes...
    when I look at some of these circuits.... what captures my attention and imagination is what they could be not what they are...
    cheers,
    msl
    - oops... - mqracing 17:21:31 10/18/05 (0)
      finished too early...
      for the output stage I would use the stereo sound recommended operating points...
      around 430 volts on the plate as I recall and about 60 mils of so of plate current. good for about 6 or 8 watts in PP.
      but that's plenty for me...
      msl
71A schematic - Joel Tunnah 06:42:19 10/14/05 (3)
Here you go Bas and Mike. And thanks for the positive remarks!
This was the second amp I ever tried to do on my own, and I think there are a couple of poor design choices. I would definitely lose the resistors in the power supply, and use audio-grade plate chokes on the 01A's, if I tried to build this again.
I did try the Hammond 1628SE with this amp, although I couldn't hear much if any difference - maybe due to rolloff from the el-cheapo 156C's.
The 5V supply was an L7805. I would try choke and cap next time.
The 40V negative bias battery for the 71A is actually thirteen 3V coin cells in series.
Overall this was a warm, fun amp to listen to, and was to this day the quietest amp I've ever built. Output was 800mW, and it was probably distorting on every peak, but it sounded so thick and full - after a little while I stopped worrying about it.
Joel
- So now I have to ask you - Russ57 11:49:41 10/14/05 (1)
  Seems like it's my month to bug you with questions:)
  I have always known you as a push pull guy (and this may be incorrect). Given that this was one of your early amps can you elaborate on why you have gone in the push pull direction? I ask because I sometimes think about doing a SET but never do for reasons that are probably invalid...like I think they won't sound neutral or have flat response...or will sound very colored. Fact is it has been soooooo long since I heard one....and I doubt I ever heard a good one.....so I am going to pick your brain a bit and see why you have made the decisions you have.
  
  Russ
  - Re: So now I have to ask you - Joel Tunnah 19:08:51 10/15/05 (0)
    I started building push-pull amps just because I wanted to learn about them - not because I didn't like SE. I now enjoy listening to PP amps more, but I have been tinkering with some new SE ideas recently. Maybe one of them will see the light of day.
    Joel
- Thanks Joel..and yes..the difference between - Bas Horneman 08:51:09 10/14/05 (0)
  "normal" plate chokes and good quality ones is massive. I gave away some Lundahls LL1667 to charity and replaced them with some surplus I got for very little ...gone was the good sounding amp..replaced by a mediocre one...So I decided to get myself some MQ EXO-01, which I will put into the amp one of these days.
  Regards,
  Bas
  To infinity and beyond!!!

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