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tinitus 1st August 2011 10:15 PM

My new humble thread
 
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I think I will try it like this

probably gets less 'google hits' than my other thread :D:)

tinitus 2nd August 2011 01:49 PM

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reading about Van Scoyoc cross coupling, I thought why not combine it with above cathodyne
haven't seen this anywhere, so I guess it won't work :scratch:

smoking-amp 2nd August 2011 06:22 PM

Needs some caps after the cathodyne for voltage isolation. Main problem will be the low and varying impedances seen by the cathodyne (due to driving the output stage cathodes) especially with the outputs operating in class AB.
With some Mosfet followers to drive the output stage cathodes inserted in between it could work.

Fenris 2nd August 2011 06:53 PM

Is Van Scoyoc the same as Blumlein garters?

Miles Prower 2nd August 2011 09:16 PM

Quote:

Originally Posted by Fenris (Post 2658551)
Is Van Scoyoc the same as Blumlein garters?

No. The Van Scoyoc was an overly complicated phase splitter, and the Blumlein Garter circuit was a cathode biased arrangement that automatically balanced plate bias currents. Two different things.

tinitus 2nd August 2011 09:25 PM

Quote:

Originally Posted by Miles Prower (Post 2658713)
The Van Scoyoc was an overly complicated phase splitter

I guess uoy refer to the cathode follower design
I believe it was done because of the need for a low impedance drive

from what I understand a trafo or interstage was originally used to 'drive' the Van Scoyoc splitter
the more complicated cathode follower design was implemented instead of the 'simpler' trafo

thats why I thought 'hey, cathodyne has low impedance too', right ?

but in my suggestion its the output stage that have cross referenced cathodes, and not the phase splitter
so it might be a completely different thing
but I don't know

tinitus 2nd August 2011 10:28 PM

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ok, different approach

transformer/autoformer used as phase splitter seem to become more popular

this one uses a relatively cheap interstage in a parafeed manner
and the secondary is used to cross reference output cathodes, in a kind of Van Scoyoc style

I suppose the IT is less critical this way
but is it possible ?

tinitus 3rd August 2011 01:07 PM

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and, slightly different

Miles Prower 3rd August 2011 07:22 PM

Quote:

Originally Posted by tinitus (Post 2658722)
I guess uoy refer to the cathode follower design
I believe it was done because of the need for a low impedance drive

from what I understand a trafo or interstage was originally used to 'drive' the Van Scoyoc splitter
the more complicated cathode follower design was implemented instead of the 'simpler' trafo...

You have to consider the times when circuits such as the Van Scoyoc (and another one, the Isodyne) were developed. That was before the availability of decent solid state devices. There were no constant current ICs, no BJTs at all, and if there was anything, it would have been the noisy, unreliable, unstable point contact transistor.

They didn't have anything that could have served as a CCS for an actively loaded LTP. They were trying to solve problems that have much simpler solutions today.

Also, any time you have cross coupled feedback, you have a potential astable multivibrator.

smoking-amp 3rd August 2011 07:35 PM

The circuit in post 8 is looking better. The coupling xfmr needs to have a low output Z to drive the cathodes. And as Miles mentioned about cross coupled feedbacks turning into a multivibrator, the turns ratio for the low Z out xfmr would need to be low enough to keep the loop gain around the cross-coupled loop less than 1. Ie, the cathode currents must not excite their own grids with enough voltage to keep it oscillating. With the loop gain kept just below unity though, it may bootstrap the input impedance to eliminate loading on the 1st tube stage. Might be an interesting design concept.


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