Sorry for my late reply, but I just take a look at your thread...
There are two bad "things" in your schematic:
p.1. MOSFET follower
p.2. N feedback (more harmful than p.1)
Good driver stage for russian GM70 and 211 direct heating triode is loftin-white schematic with russian 6N6P double triode, Tungsol/RCA 5687 or similar double or two single triodes...
There are two bad "things" in your schematic:
p.1. MOSFET follower
p.2. N feedback (more harmful than p.1)
Good driver stage for russian GM70 and 211 direct heating triode is loftin-white schematic with russian 6N6P double triode, Tungsol/RCA 5687 or similar double or two single triodes...
I think we would all hear your opinions on those two things, possibly supported by scientific proofs and measured data.
You Talkin' 'Bout Me
I assume you mean my preliminary design for an 845 SET, since mine was the only one that included gNFB. On your two points, I gotta disagree.
Followers (cathode/source/emitter) are the least offensive type of stage. With the Source Follower, you avoid the problems of Cgs nonlinearity since the gate and source are at nearly the same potential. Unlike the Emitter Follower, the input impedance is not dependent on the load at the output. It is better than a Cathode Follower since the MOSFET has much higher gain, therefore, a much lower Zo. Low Zo is desireable for driving the finals into Class A2. The lower, the better. MOSFETs do that very well. I'm not a "sandophobe", and will use SS when/where it does the job at hand the best.
As for p2, rejecting gNFB is just plain nutz. Now, it is quite true that the technique has gotten a bad rep due to its misuse by lazy designers who try to compensate for a bad fundamental design by simply pouring it on in a misguided attempt to sweep those fundamental design flaws under the carpet. Unforch, they also sweep away a lot of the details of the program material. This is not a good thing.
However, there is no doubt that gNFB can make a good design even better. Now, you might argue that, since the 845 has an r(p)= 1700R, that it isn't necessary. However, you can improve speaker damping by getting that Zo down with NFB. Isn't poor bass performance a big complaint against SETs? Why put up with that? Also, active device nonlinearities and the nonlinearities of magnetics are unavoidable. gNFB can compensate. There is no good reason not to use it.
Yes, I know that it's "heresey" in a SET. But heresey be damned! That's how I intend to design 'em. I want something that sounds really good, and that's what gNFB does best: make a good design sound even better.
widowmaker said:
I assume you mean my preliminary design for an 845 SET, since mine was the only one that included gNFB. On your two points, I gotta disagree.
Followers (cathode/source/emitter) are the least offensive type of stage. With the Source Follower, you avoid the problems of Cgs nonlinearity since the gate and source are at nearly the same potential. Unlike the Emitter Follower, the input impedance is not dependent on the load at the output. It is better than a Cathode Follower since the MOSFET has much higher gain, therefore, a much lower Zo. Low Zo is desireable for driving the finals into Class A2. The lower, the better. MOSFETs do that very well. I'm not a "sandophobe", and will use SS when/where it does the job at hand the best.
As for p2, rejecting gNFB is just plain nutz. Now, it is quite true that the technique has gotten a bad rep due to its misuse by lazy designers who try to compensate for a bad fundamental design by simply pouring it on in a misguided attempt to sweep those fundamental design flaws under the carpet. Unforch, they also sweep away a lot of the details of the program material. This is not a good thing.
However, there is no doubt that gNFB can make a good design even better. Now, you might argue that, since the 845 has an r(p)= 1700R, that it isn't necessary. However, you can improve speaker damping by getting that Zo down with NFB. Isn't poor bass performance a big complaint against SETs? Why put up with that? Also, active device nonlinearities and the nonlinearities of magnetics are unavoidable. gNFB can compensate. There is no good reason not to use it.
Yes, I know that it's "heresey" in a SET. But heresey be damned! That's how I intend to design 'em. I want something that sounds really good, and that's what gNFB does best: make a good design sound even better.
Giaime said:
It would be a good thing if more folks learned how to use the quote feature. 😉
Except for the hybrid Kimmel, it looks very similar. Great minds think alike. 😎
As I have stated on my web site, the PowerDrive circuit can be adapted to many different designs. Because of this each one is slightly different from the others. This is usually because of the different voltage and power dissipation requirements. This means that several different PC boards would be required to cover all of the different cases. The economics of PC board fabrication, and the time required to prototype and test each different layout, do not allow for me to offer these PC boards at this time.
The PowerDrive circuit is simple enough to be constructed on perf board or even careful point to point wiring. This has been done by other DIY'ers.
I have not tried the PowerDrive with an 805, since I do not have any 805 tubes. It should work (and sound great) based on my experiences with similar transmitting tubes.
I have not tried using the CCS in a cathode follower circuit, although others have suggested it here, and possibly even tried it.
Following with this link, I would like to understand how can run in A2 condition the 211, in my last amp driving with 6e5p at 30mA when grid into positive the waveform begin to deteriorate as clipping situation, now driving with interstate LL1660 2A3 - ll1660 - 211
The situation is similar, a little bit better, but far from A1 when wave is perfect.
the question to understand which condition need the driver to run the 211 in A2 ?
The situation is similar, a little bit better, but far from A1 when wave is perfect.
the question to understand which condition need the driver to run the 211 in A2 ?
thanks Euro
In my new amp with 2a3 LL1660 211,
Low impedance < than ??
Interstage 400ohm enough ??