Kappler phase inverter

[banat]

Stumbled over this very rare type of phase inverter and I wonder why is not used more frequently ? , want to try performance from that Kappler phase inverter type but formed from one EF86 tube and one ECC82 or ECC81 tube driving four EL34 tubes connected as conventional 70W PP- UL output power stage , your`s opinions ,experiences and suggestion are welcome .

 

[rayma]

It's just a concertina phase splitter, with a cathode follower buffer for the higher impedance (plate) output.
The buffer won't do much for most circuits, which usually have equal impedance loading of both outputs,
and hence equal frequency response, even with the unequal source impedances of the plate and cathode.

Using the CF buffer will unbalance the outputs somewhat due to the CF having less than unity gain.
The filaments of the concertina and the cathode follower will also need to be elevated for low hum.

 

[banat]

And I have read somewhere that optimum Rk value for that buffer 6SN7 one triode actually is sum of Ra+Rk values of that concertina PI triode , 47K+47K=94k and not 100K as is in that schematic .

 

[rayma]

With tubes, optimum is in the eye of the beholder. Tolerances are rather high.
Maybe their idea is to null the combined power supply current draw.
Or the CF could instead have a separately filtered power supply terminal.

 

[Merlinb]

Because it doesn't work very well. The cathodyne always relies on equal loading at each output, which the Kappler undoes, i.e. it makes things worse. He was trying to fix a problem that doesn't exist. If you need buffered outputs you need to buffer them both equally.

 

[jcalvarez]

That 6SN7 could be put to better use as an LTP.

 

[banat]

Because it doesn't work very well. The cathodyne always relies on equal loading at each output, which the Kappler undoes, i.e. it makes things worse. He was trying to fix a problem that doesn't exist. If you need buffered outputs you need to buffer them both equally.

Well than for my amp I need to engage one more double triode connected as CF for buffer stage .

 

[banat]

That 6SN7 could be put to better use as an LTP.

Well that`s good solution , think input EF86 triode wired further to DC connect to grids of 6SN7 (or ECC82 or ECC81) connected as LTP , similar as is done on Mullard 5-20 amp.
, still this very rare Kappler PI is chalenge for me to try his performances ...

 

[jhstewart9]

Here is yet another, popular in Europe but didn't get much use on this side.