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Another idea :-) [message #30048] Sat, 25 December 2004 14:54 Go to next message
Damir is currently offline  Damir
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Registered: May 2009
Illuminati (2nd Degree)

Well, how about "enhanced" SRPP, with anode choke in the "upper" Rk position? "Ordinary" SRPP has good features (simple, direct coupling between triodes, every tube has B+/2 and the same Ia, "upper" tube is load for the lower tube and cathode follower at the same time, etc.), but Rl for the lower tube is not CCS, actually pretty low with lower mu tubes: Rl=rp+(mu+1)Rk.
If we use CCS or anode choke (choke impedance Z=2Pi*f*L)for "upper" Rk, then this high Rk is further "multiplied" with upper tube mu, and we have very large Rl (A~mu, low distortion) and very low output resistance. We can use anode output on the lower tube, too.
Schematic shows values for the "Lundahl" LL1668 choke (100H,25mA and 680 Ohms DC resistance, Rw). We don`t have to use the same Rk like Rw, or the same Uak, or even the same tubes. It`s desirable that Rw is low, with values on the schematics we`d get about 11mA through SRPP. Nice thing is that choke parameters (L,Cw...) are not that critical in this (SRPP) position like in the anode load use.
But, I don`t have any plate choke to try it in the real world. We need a volonteer to actually try it. (If we use the same double triode for lower and upper tube, then our heater supply must be "referenced" to about 90V - better use one 5687 for both lower triodes and another for upper, the upper Uh referenced to about 200V.).


Re: Another idea :-) [message #30049 is a reply to message #30048] Sun, 26 December 2004 13:27 Go to previous messageGo to next message
colinhester is currently offline  colinhester
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Registered: May 2009
Location: NE Arkansas
Illuminati (3rd Degree)
Found this link regarding SRPPs. Thought it might be of interest.....Colin

Re: Another idea :-( [message #30051 is a reply to message #30049] Sun, 26 December 2004 16:33 Go to previous messageGo to next message
Damir is currently offline  Damir
Messages: 1005
Registered: May 2009
Illuminati (2nd Degree)
Huh, I lost my concentracion few times, but I read it (+ another SRPP article from 2000.). Hm, the author analysis shows more or less negative results...
I can`t say that choke version works good or not, as I said - I didn`t try it. If it means anything, some people (who built this circuit) claim good results, especially with anode output...


Re: Another idea :-( [message #30056 is a reply to message #30051] Mon, 27 December 2004 10:30 Go to previous message
colinhester is currently offline  colinhester
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Registered: May 2009
Location: NE Arkansas
Illuminati (3rd Degree)
You made it further into the article than I did. I wouldn't be too bumbed about the author not liking the topology. It's just one person's opinion, and like you said, other have had good results.

I just posted it as a technical reference.....Colin

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