Weird Phase inverter...

[DummyLoad]

e. rondehuis presents an "interesting" phase inverter in his book "valves for audio frequency amplifiers". it's a reprint by the audio amateur press.

the use of heptode is weird enough, but the arrangement kind of baffles me. i wish i had a scanner to scan in the original schematic, but i don't. i redrew the schematic. i hope it is a faithful redux of the original. if you have some time and the spare scratch, pick up a copy of the book; it's a decent read for  novice level builders. it can be obtained from antique electronic supply.

in the plan the designer used an ECH21 for the phase inverter - why, i have NO idea. it's a weird-ass tube - a loktal no less, and the common cathodes are brought out on the locking/guide pin - base is all metal so is the locking in - duh! ;)

http://tubedata.milbert.com/sheets/030/e/ECH21.pdf

what in the sam hell is going on? some sort of long tail with out the tail? common cathodes but biased conventionally? paraphase of the weirdest kind - how about that P3 to "balance" the PI - i'm guessing that's what that's for?

scanning through the text, he makes no mention of what the values are for L1 - the author presents another design example of a 35W EL34 amp w/ similar supply and used the 8H 50mA choke - so snatched the value from that.

much thanks in advance for any enlightenment.

peace.

--DL

[PRR]

Heptode is working like a pentode. Plain gain stage.

Triode is an ordinary floating paraphase. 1Meg+1.1Meg set it up as a unity-gain inverter. The 10% difference accounts for triode gain being closer to 10 than to infinity.

The common cathode network may have to be heavily bypassed to avoid instability.

[PRR]

'pears to be directly copied from page 5 here?
http://tubedata.tubes.se/sheets/046/u/UCH21.pdf

Same idea but only converter service shown:
http://www.r-type.org/pdfs/6aj8.pdf

[DummyLoad]

The common cathode network may have to be heavily bypassed to avoid instability.

that's what threw me, the shared cathode, nearly all paraphase i've seen don't share cathode.

much thanks PRR, i see what's going on now. 

btw, not something i'd go out my way to build for hi-fi or guitar. it was posted solely for educational enlightenment. 

--DL

 

[rzenc]

that's what threw me, the shared cathode, nearly all paraphase i've seen don't share cathode.

i'm building - one more  ! - 5E9A, and it is an example of paraphase sharing cathodes.

http://www.el34world.com/charts/Schematics/files/fender/TREMOLUX_5E9A.pdf

Best Regards

rzenc