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Old 16th November 2008, 05:13 PM   #1
nickds1 is offline nickds1  England
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Default Triode strapping a tetrode...

Hi,

I've some RCA 7094s that I'm thinking, for various reasons, of strapping as triodes... in a fairly electrically harsh environment...

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
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Old 16th November 2008, 05:31 PM   #2
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Per the 7094 data sheet, g2 is rated for only approx. 1/4 the voltage that the anode can take. Tie g2 to the plate with a 10 KOhm Mills MRA-12. Doing that should ensure that screen grid dissipation does not become excessive.

Talk about things being relative, in this situation, a g2 rated for 20 W. is (sic) fragile.
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Old 16th November 2008, 10:09 PM   #3
gianis is offline gianis  Greece
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Quote:
Originally posted by Eli Duttman
Per the 7094 data sheet, g2 is rated for only approx. 1/4 the voltage that the anode can take. Tie g2 to the plate with a 10 KOhm Mills MRA-12. Doing that should ensure that screen grid dissipation does not become excessive.

Talk about things being relative, in this situation, a g2 rated for 20 W. is (sic) fragile.

7094 a amazing tube by RCA..
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Old 16th November 2008, 10:24 PM   #4
nickds1 is offline nickds1  England
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Quote:
Originally posted by gianis
7094 a amazing tube by RCA..
..It's lovely, but I have nasty plans for them...

(well... one of them...)
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Old 16th November 2008, 10:43 PM   #5
gianis is offline gianis  Greece
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Quote:
Originally posted by nickds1


..It's lovely, but I have nasty plans for them...

(well... one of them...)

Try two of them in PP topology . as RCA
suggest,.,, [with some amount of feedback.....]
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Old 16th November 2008, 11:28 PM   #6
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Default Re: Triode strapping a tetrode...

Quote:
Originally posted by nickds1
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.
Makes no difference, you still get a pseudotriode either way. Just make sure you don't bust specs for the G2 ratings. If there aren't any plate characteristics for triode operation, you'll have to make your own to pick loadlines and Q-Points.
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Old 17th November 2008, 12:49 AM   #7
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There are triode curves in the datasheet that was linked by Eli. It states for triode strapping to connect g1 and g2 together instead of g2 to the plate, and running it in A2 (positive grid bias).
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Old 17th November 2008, 01:35 AM   #8
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Quote:
Originally posted by jerluwoo
There are triode curves in the datasheet that was linked by Eli. It states for triode strapping to connect g1 and g2 together instead of g2 to the plate, and running it in A2 (positive grid bias).

It seems I did not look far enough down on that PDF. I stopped after seeing the max. voltage numbers. That g1/g2 tie is somewhat similar to what can be done with the type 46.

FWIW, tieing g2 to the plate with a proper resistor should work.
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Old 28th December 2008, 12:45 AM   #9
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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.

The act of tying the 2nd screen and plate together reduces the power dissapation of the plate ( a typical 6v6 drops from 13 watts to about 10) .

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.

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.


Anyone have any thoughts on this ? Is it feasible ? Anything I might want to consider before trying it ?


I see the 7094 recommends positive voltage , while typically one would use negative. Any thoughts on that for use with the 6P6S ?


...........................Blake
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Old 28th December 2008, 05:06 AM   #10
Vlauga is offline Vlauga  Russian Federation
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6N6C ...? 6H6PI this is double triod.

6P6S = 6V6
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