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ping Mike, about that Altec 1570B amp

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Hey Mike,
I was scribbling away at PP811A ideas, inspired by Jim Doyle's (?) post a while back, trying to shoehorn the whole thing into a 3-stage direct coupled compact (6SN7-6A5Gcf-811A), and then I come across this link at Ned's site. Well, well. Look at that "17173" sitting in the driver cathode circuit (and there's also a 15095 on the page). The EXO-173 can't take any DC current right? So its a parafeed version of the 17173? The fifties were good for audio, I take it?
best, del sur... --keto

http://www.triodeel.com/al1570b.gif (Open in New Window)

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Re: ping Mike, about that Altec 1570B amp - gluca 05:03:49 11/24/05 (1)
KETO!!!! I do like your ideas. Yes I do! The funny thing is that a few days ago I was looking to that Altec schem trying to have inspiration for a new project as well as Jim's posts.
That’it! A rough idea not checked but just sketched. I can't do that as my power tranny would not give all the current it needs.
Please folks, just have also a look to the other idea I posted … I do really need advises.
I am wondering how long must we wait to have a MQ PP to PP interstage tranny … LOL!
Ciao Gianluca
- An idea (Open in New Window)
- Re: ping Mike, about that Altec 1570B amp - keto 05:43:34 11/24/05 (0)
  Ciao Gluca,
  How about a voltage amp stage before the 807's and drop the last stage? The 811A probably draws a little grid current all the time (this I get from staring at the data sheets, only), and as the grid swings most positive, would seem to draw 40mA or as much as 60mA (or more?), depending on the plate load.
  Now I see, you'd limit the 811A's operating range there, making the EXO-099's 10mA cathode draw a good fit.
  Mine is only idle scratching, but I'm fascinated with the idea of class B 811A, beyond the "balanced" class B of your schematic, to the PP pair switching on and off, from the sheets, of 750Vp, 5K1 a-a load and shared idle current of 36mA (probably need to plan for 300mA+ swings). And mostly, I wonder what this kind of circuit sounds like.... --keto
How about a PP:PP interstage for driving A2 grids ? - Jim Doyle 21:53:03 11/23/05 (0)
Go for... Scale down the Altec amp for like, 25W. Then you can use
off-the-shelf PP transformers and 400'ish volt supplies.
Rather than a CT choke, why not a PP:PP IT for driving the A2 grids.
The grid current is very much push-pull, so you can rely on some
level of cancellation of currents the same way you do in primary.
Why not a 3+3:1+1 stepdown. If you used a low Rp tube, like a 6BX7GT
or 6AV5GAs, then the 800 ohm plate impedance would reflect to 100 ohms which would drive the 1K ohm grid of the 811A fairly nicely.
Gee, as an experiment - why not one of the universal toroids with
dual primaries and dual secondaries. For example, 120V : 48V which
is very common for computer power supplies.
-- Jim
Re: ping Mike, about that Altec 1570B amp - Doc B. 18:59:55 11/23/05 (1)
You should see the spec for the output trans that Buddha designed for the 1570. Yeow.
- Re: ping Mike, about that Altec 1570B amp - keto 20:28:44 11/23/05 (0)
  Not of the shirt-pocket variety?
  - http://www.dvq.com/hifi/images/1570a.pdf (Open in New Window)
Re: ping Mike, about that Altec 1570B amp - mqracing 16:27:34 11/23/05 (1)
Hi Keto:
The EXO-173 and 173PPS are each based on the original Peerless 17173 ct choke.
If you were to use our EXO's in a manner like that in the schematic you mention then you could allow a dc bias current... doing this by memory I think the spec is 100 mils.
But... and a big but... our EXO (especially w/ nickel) is not going to like very much imbalance at all... and, in advance, no spec was given in the Peerless folder on max unbal.
when our EXO's are used as a phase splitter and a 1:2 or 2:1 then we advise no dc current at all... since it is "single ended" primary... and no provision has been made to allow any dc unbal current.
hope I've said this well...
msl
- Re: ping Mike, about that Altec 1570B amp - keto 20:58:29 11/23/05 (0)
  That 17173 looks to swing about 0/50-50/0mA. So you could instead put an EXO-173 before the driver (at 750Vp, the date sheet requests just that EXO-173's 150vrms swing, from grid to grid), and put separate chokes on the cathodes, with low DCR to keep the 811A grid bias near zero. That 811A is pretty versatile, the last triode hurrah... --keto

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