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K&K Audio / Lundahl Transformers

10 PP amp

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Since I have a few sets of 10's (not 801's, but could get those too) I wonder about a PP 10 amp project. The 10 is a little unconventional as it has both high gain and high plate resistance.
The three requirements I have are that the secondary be 16 ohms, that the amp have very good HF bandwidth extension, and that the amp do a harmonically authentic disappearing act. I suppose the amorphous cores are the choice.
I'd like to start planning this amp (or to ditch the 10's and do something else) and I ask for recommendations. Would also appreciate recommendations for a fine diff driver tranny as well. The driver tube types can follow the requirements that transformer presents.

Follow Ups:

Re: 10 PP amp - Ivan303 20:44:57 05/29/05 (0)
If I were going to build a PP amps from 10's, I'd stack them ala SRPP and drive them with a concertina phase splitter, plate to the top tube, cathode to the bottom.
Then take the signal off the junction of the two output tubes and through a blocking cap to a 5K parafeed OT.
Doing that with 6B4G's at the moment and it's a very nice compromise between SET and PP sound.
Run in class "A" and remember that the two output tubes are in series for DC but parallel for AC. With luck, and hum pots, you may well be able to get by with AC heaters.
As the two output tubes are in series, you'll require fairly high B+.
10s are great - Ed Sawyer 20:13:24 05/26/05 (1)
gotta love those tubes. I am interested in how it all works out. Please keep us posted and share details of design. the LL1688 also has a high impedance primary I think, which might work with the 10 as an output tube (huge overkill tranny though, I'd guess.)
10 driving 2A3 or 45 would be a cool setup. I think www.vt52.com had some info on some projects he did where he had a 10 driving a 45. not PP though , just SE.
-Ed
- Re: 10s are great - Jon Lane 16:34:27 05/28/05 (0)
  If I do use these they'll be as PP drivers for AVVT 2A3's. Will let you know...
Why not consider parallel SE? - Brian C. 13:48:20 05/24/05 (0)
This will ease the OPT requirements.
Brian (not Cherry)
Re: 10 PP amp - KevinC 09:49:00 05/23/05 (4)
Hey John!
The 10 needs pretty high primary impedance, which leaves us with the LL1620/PP or LL9202/PP. The LL1620 is really kind of low at 11.5K, so there's the LL9202/PP remaining. If you are expecting -0dB response at 20KHz, I would guess that a 23K primary is not going to give it to you. There are just too many strays at that point, even with a 16 ohm secondary. I have no firsthand experience with high impedance tubes like these, so I am just guessing based on the experience of others. However, the amorphous core will give you the disappearing act, especially combined with an amorphous core interstage.

Kevin Carter
K&K Audio
www.kandkaudio.com
- Re: 10 PP amp - Jon Lane 19:48:47 05/23/05 (3)
  Hi Kevin!
  If I sacrificed the 20Hz parameter (likely this thing would be used only to drive a 100dB custom fieldcoil mid above 500Hz) would this change anything for the better?
  Here's a another curve: Given the high Rp, is there an interstage that would more ideally mate these 10's as PP drivers into PP 2A3's? That's the other option I have.
  Lastly, any chance in either case of a single primary/single secondary tranny with A cores? Just for simplicity's sake.
  - Re: 10 PP amp - KevinC 04:33:47 05/24/05 (2)
    I'm afraid that you are still left with difficult high frequency problems due to the high primary impedance. I wouldn't be surprised to see pretty significant roll-off at 10KHz.
    But now you're talking! If you were to use PP 10s to drive PP 2A3s, I would use an LL1660SAM/PP to do the honors and run the IT 2.25+2.25:1+1 if you can get enough swing out of the 10s and don't mind losing the gain. Even 2.25+2.25:2+2 should work well, although I am a fan of low driver impedance. The 2A3s could be coupled to the loudspeaker via an LL1620AM/PP. This is good stuff!
    There is nothing to be had from Lundahl other than C-cores in this vein. And no single primary/secondary stuff either.
    
    Kevin Carter
    K&K Audio
    www.kandkaudio.com
    - Re: 10 PP amp - Jon Lane 13:27:06 05/24/05 (1)
      Okay, to be sure I understand, the 10pp driver notion, using 2.25+2.25:1+1 does not have the HF limitations due to Rp?
      For the OPT I'm afraid I have some NOS UTC LS57's so I'm set there.
      Another subject: Does Lundahl make wideband A-core SE OPT's? I'm thinking of a 45 project too...
      - Re: 10 PP amp - KevinC 09:52:44 05/25/05 (0)
        
        In Reply to: Re: 10 PP amp posted by Jon Lane on May 24, 2005 at 13:27:06:
        
        The plate impedance of the 10s is not a problem with the interstages.
        I've used LS55s, LS57s, and LS58s. Sell the LS57s on eBay and buy amorphous core outputs. The difference will be substantial in the positive direction for PP amplifier service.
        Take a look at LL1620/1623/1627/9202. All of these are available with amorphous cores gapped as per the datasheet for a variety of operating points.
        
        Kevin Carter
        K&K Audio
        www.kandkaudio.com

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