Triode strapping a tetrode...

[Tubelab_com]

Jose:

The 46 in that schematic is obviously running triode connected in class A although it is not shown on the schematic. I would be tempted to use a 45 in that design. I do have some 46's around here somewhere, but I have never connected them up. Someday....

 

[korneluk]

Teaser shot, or how I spent my Christmas vacation...

From L to R:

42, UX245, C347, RCA Radiotron 10 (dated 1939), 10Y, and VT-25A longplate.

 

[Tubelab_com]

or how I spent my Christmas vacation

Yeah, rub it in. You get to play with some nice warm tubes, while I froze my a** off in 1 degree weather. I'll be sure to post some nice glowing tubes when you get sent to Toronto!

Frozen grandson and dog:

 

[Miles Prower]

But choose to use plate to grid feedback . He must have had some good reasons for this. Can anyone give or link to more info on this subject ?

Yes, he did. The advantage to this type of local feedback is that:

A) It allows for the useage of a wider variety of finals. Doesn't matter if the screens need to run at a low voltage as compared to the plate (6L6s, 807s, most TV HD finals, just essssssssssssss loads of RF finals). It's flexible, unlike UL where the die was cast when the OPT was wound, and you just have to hope they got it right.

B) Some audio finals, like the 807 and all the 807-oids like to make high order distortion that sounds like

An externally hosted image should be here but it was not working when we last tested it.

. Local NFB clears that up pretty well. O. Schade recognized this problem in his "white paper" (which really is an advert).

Beam Power Tubes

 

[Miles Prower]

I was gonna post a new thread about this, but was told to search before posting. After reading this, I see it isn't so far fetched.

I am running Russian 6N6C's (6p6s).Has anyone ever tried connecting the two screens together as a giant input screen, and run the tube in "triode" like that ?

Dunno why I thought of it, but it seems to have some good and bad effects. The screens are much closer together than the 2nd screen and plate (which are usually tied together to run "triode") , which would seem like a good thing as far as time coherance.

Connecting all the screens in parallel is done all the time for RF amps. This connection makes a high-u pseudotriode with the power sensitivity you like to see in RF applications. It might even allow for zero bias operation. For audio, it ain't so great. Like any high-u triode, the r(p) will be very high (poor damping) it will have a greater tendency to make high order distortion, and may require positive bias, Class A2.

Paralleling the screen with the plate makes a low-u pseudotriode with the desireable low r(p) and allows for Class A1 operation.

What I envision by having the tube hooked up this way (screens tied together) is a larger input screen area , a higher power level available (as in tetrode mode) , and a higher output Z , like when run in tetrode.

It'd be like using a 811A high-u RF "zero bias" triode as an audio final.

Seems as though the act of tying the 2nd screen to the plate is kind of silly. While it offers the reduction of output Z , it dramatically reduces power handling/output , and would seem to create a hazy output (time coherance ) due to the large difference in spacing between it and the plate.

Transit time effects don't become important until you're pushing 100MHz+ For audio, makes no difference.

 

[triode_al]

Hi,
I'd appreciate any tips on this - I've looked in the usual places, but everything seems to be for strapping pentodes and my knowledge doesn't go far enough to extrapolate this to tetrodes.

Cheers

Nick,
if you look up pentode/tetrode build it is the same (imho).
The quoted connection of a high value resistor to anode is well documented.
Around 1980 I used a 814 in a directly strapped mode, with a low Vb of course. I wrote an article in our local magazine about it.
But because of the high grid current that then arises (easily 1 mA!!) there is need for a directly coupled driver. I used an SRPP alike stage for that. This sounded good, punch. I took feedback from the anode to the input cathode.
Having a transformer or a choke load is OK too.

having these very large tubes is teasing but trickles the phantasy.
albert