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Old 12th March 2011, 06:06 PM   #11
DualTriode is offline DualTriode  United States
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Hello,
Yes it looks very much like a SRPP. It also looks much like a Mu-Follower. Both SRPP and the Mu-Follower are discussed on other pages (i will scan and post if there is an interest).

When I ran it in B2 spice it was not constant current. The top tube acted very much like as a grounded cathode amplifier with a plate resistor that has a voltage drop of half the B+ voltage, as described in the attached PDF above. It acted very much single ended but with less harmonic distortion. Push-Pull will deliver more current at the output. The maximum current swing for single end is plus minus the idle current. Push-pull is greater, in theory double the idle of one of the valves of the pair.

SY, much of this is vanity in The Old Testament sort of way, much has been done before. This is old school stuff. The plan is to avoid driving the power SET into A2 and keep the input impedance steady to retain as much linearity at the driver as possible.
I have a sheet of aluminum laid out to start drilling holes for the tube sockets.
DT
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Old 12th March 2011, 06:19 PM   #12
SY is offline SY  United States
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Problem is, the output stage is a reactive load and that, along with the loads R5 and R9 (what does R5 do?) will compromise the linearity of that stage. A buffer (you might consider MOSFET if metal is already cut) will clean things up significantly and let you realize the potential high performance of the stacked triodes.
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Old 12th March 2011, 07:01 PM   #13
DualTriode is offline DualTriode  United States
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Hello SY,
Story be told, metal cut or not, this is a breadboard toy. This will be the first set of real experiments with a PC / sound card based audio test system on my bench. I plan to look at this stacked triode, power supplies, noise and distortion.
The kid in me wants to beat this with a 4 oz ball peen hammer and watch what happens on the computer output. Put more academically, how much will be compromised, without the buffer, I want to see?
The thought regarding R5; R5 is a high value bleeder to drain the coupling capacitor. I will put my feigner in there without thinking.
Please tell me more of the MOSFET buffer how would it be implemented?
DT
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Old 12th March 2011, 07:43 PM   #14
SY is offline SY  United States
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Quote:
Originally Posted by DualTriode View Post
Please tell me more of the MOSFET buffer how would it be implemented?
Topologically, this is the easiest way and will work fine, but with a negative supply available, you could put the follower on the other side of the coupling cap and have the option of A2 operation as well as better overload recovery. If you go the easy route (recommended for your first go-round), you could use something like an IRF820, a gate stopper of 1k or so, and a source resistor of B2+/2I, where I is the desired mosfet current (I'd use 10mA or so to start).
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File Type: png mosfet follower.png (6.2 KB, 339 views)
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Old 12th March 2011, 11:31 PM   #15
pieter t is offline pieter t  Netherlands
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Quote:
Originally Posted by SY View Post
Broskie uses a White cathode follower with a hum cancellation gimmick.....
I am not so sure that Broskie's Aikido output stage is a White CF.
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Old 12th March 2011, 11:36 PM   #16
pieter t is offline pieter t  Netherlands
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Actually I am sure it isn't; it does not have the "internal" feedback loop of the WCF, and will not have that low output impedance.
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Old 13th March 2011, 06:09 PM   #17
DualTriode is offline DualTriode  United States
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Quote:
Originally Posted by pieter t View Post
I am not so sure that Broskie's Aikido output stage is a White CF.
Hello,
peter t,
Being an old grump I was still born too late to put my name on any of these tube circuits. There seem only to be a few basics and variations on a theme.
Looking back with most of the patents expired perhaps there should be a new naming system sorts the circuits by performance characteristics; input impedance, output impedance, (oops) miller capacitance, gain or buffer. Blah blah blah.
The Aikido Cathode Follower seems to be a unique variation of the cathode follower. If I recall correctly the WCF is also push pull.

Sy,
Thank you for the MOSFET buffer implementation. It will be interesting to test the grounded cathode, stacked MIT triode thing, with and without buffer.
A continuation of a related thought; in a two stage SET amplifier the stages are 180 degrees out of phase. The transfer functions curve in opposite directions and tend to cancel each other out and will create a composite transfer function.
This will be tweeking without the drugs.
DT
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Old 20th March 2011, 02:16 AM   #18
DualTriode is offline DualTriode  United States
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Hello,
This thing is taking longer to fabricate than I wanted it too. The solder smoke is thick however it is only ~ 75% complete.
I have installed a 100 ohm resistor (wobble stopper)at each of 3 grid pins for each tube 8532.
DT
All just for fun!
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