• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

SS phase splitters?

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Eli Duttman

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Joined 2004
It's no secret that I like MOSFET voltage followers. As a "concertina", AKA split load, phase splitter is a tweaked voltage follower, a MOSFET doing that job rates to be quite satisfactory. Look here, where Jeff Yourison is working (with a little help from yours truly) on a PP 6Y6 amp that employs a MOSFET "concertina" phase splitter.

While FET current amplifiers are highly satisfactory, I'm very dubious about FETs as voltage amplifiers. The cross coupled phase splitter is a somewhat complex bit of circuitry. Voltage amplification is occurring, along with the generation of the 180o out of phase signals. I can see depletion mode (for self biasing ease) MOSFETs source followers at the I/P of the transformerless version, but linear triodes being employed in the voltage gain positions. Perhaps the DN2540N3-G would be suitable in the voltage follower "slots".
 
I

ingenieus

Member
Joined 2011
Here is am improved version of the Van Scoyoc cross-coupled splitter published in 1957:

http://www.next-tube.com/articles/cci/cci_EN.pdf

I ran it through LTspice, and it works perfectly. The only thing is, I don't get the bit about "cathode voltage of power tubes must be increased by 20 volts." My limited knowledge of tubes does not help, especially since the simulation works without this. Why is that necessary? To improve the voltage swing range? In practice, would this be implemented with voltage divider resistors off B+?
 

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E

Eli Duttman

Member
Joined 2004
The only thing is, I don't get the bit about "cathode voltage of power tubes must be increased by 20 volts."
Click to expand...

The phase splitter's O/P cathode followers and the O/P tubes' control grids that are DC coupled to them "sit" at +20 VDC. Correct operation of a tube, with few exceptions, requires the control grid be negative with respect to the cathode. Implicit in the remark is a cathode (self) biased set up. Since the control grids of the O/P tube pair are at +20 V., instead of 0 V., the cathode has to be raised above ground 20 extra volts to achieve the desired operating point. :yes:

If the cap. coupled O/P cathode followers are replaced by DC coupled ZVN0545A source followers, cap. coupling to the O/P tubes' grids can be employed and any valid biasing method will work. :)
 
M

MiiB

Member
Joined 2005
raidho.dk
'The last circuit is a LTP, to me one of the best ways to make a phase splitter. I would make it with two lsk170's or something like that, then cascode it with transistors that can withstand the high(ish) voltage.

Or maybe looking to Calvin's fine buffer-thread make it with a CFP pair as input + a shielding cascode. Then you can run the output tubes without any coupling caps.
 
I

ingenieus

Member
Joined 2011
Cookj said:
Novotone - Projects 35 and 37

Published in Electroniqe Pratique

Cheers

John
Click to expand...

I can read Dutch and Flemish, but my French is non-existent. It's a shame because it seems like the site contains a lot of useful information.

I eventually managed to figure out that one needs to click on "Schéma de l’amplificateur" to see the schematic of the amplifier. Here are the actual links. ;)

http://www.novotone.be/_site/projets/Projet35/Fig02.pdf

http://www.novotone.be/_site/projets/Projet37/Fig02.pdf
 
M Gregg

M Gregg

Disabled Account
Joined 2010
Thanks for the input so far,

Great ideas and circuits.:)

I was wondering how easy/hard it would be to implement, (reduce space) with some of the more complex splitters. Nice to see other examples.
Theoretically I guess you could build a whole tube circuit with FETS I wonder if anyone ever has and what it sounded like (Off topic) FET with OP Tx.
Back to phase splitters the small 6V6 is interesting.

Regards
M. Gregg
 
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