This looks like the ideal driver tube:
http://frank.pocnet.net/sheets/093/6/6S4A.pdf
I'm thinking 6922 > 6S4A > 300B
http://frank.pocnet.net/sheets/093/6/6S4A.pdf
I'm thinking 6922 > 6S4A > 300B
6s4a is my all time favorite driver tube for electrostatic
headphones. As a 300b driver it should work well, but the
extra voltage it is capable of is very much wasted on a 300B.
2 sections of 6sn7 in parallel has more drive capability and the
300B really wants that when you go into positive grid drive
current.
headphones. As a 300b driver it should work well, but the
extra voltage it is capable of is very much wasted on a 300B.
2 sections of 6sn7 in parallel has more drive capability and the
300B really wants that when you go into positive grid drive
current.
Hi,
Parallel triodes aren't exactly paradise either...
The 6S4 is the predecessor of the 12B4, plenty of juice to drive a 300B, I reckon.
Cheers, 😉
Parallel triodes aren't exactly paradise either...
The 6S4 is the predecessor of the 12B4, plenty of juice to drive a 300B, I reckon.
Cheers, 😉
IIRC it's about 2x6SN7 or 12AU7. Speaking of which, I'm suprised Frank would suggest it, I'm told it looks like a 6C4 on steriods! Graphs look like it.
Tim
Tim
Hi,
No, Tim. Two sections of a 6SN7, not two 6SN7s.
So what if it "looks" like that ?
And what on earth has it got to do with me at all?
Do you have the same kind of remarks for it's cousin, the 12B4 too?
Cheers, 😉
No, Tim. Two sections of a 6SN7, not two 6SN7s.
So what if it "looks" like that ?
And what on earth has it got to do with me at all?
Do you have the same kind of remarks for it's cousin, the 12B4 too?
Cheers, 😉
As far as I'm concerned, 12B4 is very different from it. Far more current (well... as I recall) and a radically different construction.
What has your prejudice against 12AU7 got to do with anything.. 🙄
Tim
What has your prejudice against 12AU7 got to do with anything.. 🙄
Tim
Hi,
So? Historically one was a successor to the other.
Prejudice has got nothing to do with it, measurements do.
Cheers,😉
So? Historically one was a successor to the other.
Prejudice has got nothing to do with it, measurements do.
Cheers,😉
Has anyone got the tools to simulate this circuit before I build it?
Any of the experts out there have a simulation tool that can handle this circuit. 😕
I would like to assemble this weekend if it looks feasable.
The current sources will be a Supertex Enhancent mode FET.
Power Supply and a 1 minute delay circuit for the B+ are complete and tested, I will draw them out over the next few days.
Any of the experts out there have a simulation tool that can handle this circuit. 😕
I would like to assemble this weekend if it looks feasable.
The current sources will be a Supertex Enhancent mode FET.
Power Supply and a 1 minute delay circuit for the B+ are complete and tested, I will draw them out over the next few days.
Here is the circuit after some minor tweeks
All filiments are DC.
1 minute timer for B+
Constant Current Source found at
http://home.zonnet.nl/horneman/mosfet.htm
All filiments are DC.
1 minute timer for B+
Constant Current Source found at
http://home.zonnet.nl/horneman/mosfet.htm
Attachments
Hi MikeT, did you ever build this amp?
I like the 6s4a (I have an amp using 6s4a as power tube and it sounds great). I also built a 6s4a WOT preamp and I like it.
Am thinking of building a 300 SE with 5687 input tube and 6s4a as driver.
What do you think guys?
I like the 6s4a (I have an amp using 6s4a as power tube and it sounds great). I also built a 6s4a WOT preamp and I like it.
Am thinking of building a 300 SE with 5687 input tube and 6s4a as driver.
What do you think guys?
6S4 is a good looking triode, but is designed for 150V operation, and a limit of 160V.
Meanwhile the 300B is normally biassed at -60 to -80V, and to allow some margin, the driver must be able to swing +/- 100V. With anode voltage = 150V idle, 6S4 can manage the negative swing, but going +ve, the curves become obviously nonlinear above 200V or so, even if CCS loading is used.
Only high quality option is to try a series cascode, which is what the tube was designed for. IME, an NPN transistor in the upstairs position is best here.
Meanwhile the 300B is normally biassed at -60 to -80V, and to allow some margin, the driver must be able to swing +/- 100V. With anode voltage = 150V idle, 6S4 can manage the negative swing, but going +ve, the curves become obviously nonlinear above 200V or so, even if CCS loading is used.
Only high quality option is to try a series cascode, which is what the tube was designed for. IME, an NPN transistor in the upstairs position is best here.
Tung Sol datasheet for 6S4 says 500V max. GE datasheet for 6S4A says 550V max. The 6S4 is a terrific driver tube and can even make a pretty decent output tube. You'll be interested to see its use in the upcoming 4th edition of "Valve Amplifiers."
I was hoping it was an octal, should have known better.. 😀
Linearity looks really good, and sufficient power handling for the likes of a GM70 driving it somewhat into class A2.. A 300B should be a walk in the park.. 😀
Linearity looks really good, and sufficient power handling for the likes of a GM70 driving it somewhat into class A2.. A 300B should be a walk in the park.. 😀
Thanks Kevin and SY, I will breadboard the 300B amp, either 6sn7 or 5687 for input, 6s4a driver, 300B output.
I need to gather parts, this will be an exciting project! 😀
I need to gather parts, this will be an exciting project! 😀
A naïve question:
Does the 300B really need a driver? Isn't there a nice pentode that can do duty as a voltage gain stage and have enough current, too?
Does the 300B really need a driver? Isn't there a nice pentode that can do duty as a voltage gain stage and have enough current, too?
"Linearity looks really good"
Umm, did you look at the 3rd page of the datasheet? The Mu curves are horrendous. Not even constant Mu at constant current. Should work OK for P-P, but SE looks like a disaster. As suggested earlier, it looks just like a bigger version of a 6C4.
http://frank.pocnet.net/sheets/093/6/6S4A.pdf
http://frank.pocnet.net/sheets/093/6/6C4.pdf
Umm, did you look at the 3rd page of the datasheet? The Mu curves are horrendous. Not even constant Mu at constant current. Should work OK for P-P, but SE looks like a disaster. As suggested earlier, it looks just like a bigger version of a 6C4.
http://frank.pocnet.net/sheets/093/6/6S4A.pdf
http://frank.pocnet.net/sheets/093/6/6C4.pdf
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"The test bench says otherwise."
Well, if the 6S4A datasheet is to be believed, it might work for 2nd Harmonic driver cancellation with the 300B. Has very high 2nd harmonic like a 12AT7.
Well, if the 6S4A datasheet is to be believed, it might work for 2nd Harmonic driver cancellation with the 300B. Has very high 2nd harmonic like a 12AT7.
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