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Triode strapping a tetrode...

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nickds1

nickds1

Member
Joined 2005
nick.desmith.net/
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
 
Miles Prower

Miles Prower

Member
Joined 2005
dolphin-hsl.com
nickds1 said:
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.
Click to expand...

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.
 
E

Eli Duttman

Member
Joined 2004
jerluwoo said:
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).
Click to expand...


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.
 
N

Nihilist

Member
Joined 2006
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
 
V

vega65

Member
Joined 2007
Have you considered shade's paper on beam power tubes? ( Download from s millets site , sorry dont have the link on my mobile phone ,I am in the mountains ).In the last part of that impressing paper , there is a discussion about how to alter ra .Shade does not use the more common connections to achieve triode like behaviour . 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 ?
 
Merlinb

Merlinb

Member
Joined 2006
lulu.com/spotlight/valve_wizard
Nihilist said:
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) .
Click to expand...

What do you mean connecting the "screens" together??
There is only one screen grid in a tetrode, which, as you say, is connected to the anode for triode operation. (Are you talking about the supressor grid (g3)? but the 6P6S is a beam tetrode, not a pentode.)

Running in triode mode doesn't reduce anode dissipation, since this is related to the mass of of the anode/screen grid, what data sheet are you looking at for the 6V6??
 
K

kenpeter

Member
Joined 2007
I've seen one Telefunhken LS-50 datasheet showing curves for
G1=G2... I don't know if those curve shapes are typical. However
the LS-50/GU-50 are true pentodes and not beam tetrodes. The
main diff far as it matters here, the screens are NOT aligned.

If you were running a beam power tetrode, with aligned grids,
the question must be asked: Is G2 still safely in the shadow?
Or now directly in the FOCUS of a positively charged G1? Does
this alignment put G2 in harms way?

Then again, drive voltages for G1=G2 are very low, so it may
not matter a bit of extra current? I don't know the answer.
 
Tubelab_com

Tubelab_com

Member
Joined 2005
tubelab.com
There was a thread where this was discussed a few months back, but I can not find it now. I recalled seing an amplifier schematic a long long time ago that tied G1 and G2 together through a resistor. This was called a "high mu triode connection" and I believe that it used an 807 or 6L6 type tube. I mentioned this in that previous thread and someone posted that schematic, so this has been done before.

I breadboarded that design at least 15 years ago and decided that it wasn't very useful, and was somewhat tempermental. I was building mega power guitar amps back then, so my decision criteria may have been different than today.

Over the summer several tube vendors ran tube sales with some sweep tubes for as low as 98 cents each. I got a bunch and experimented with conventional grid drive, screen drive, and briefly G1 = G2 drive. Both G1 = G2 drive experiments ended abtuptly with exploded drive mosfets, so this may not work with all tubes.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=128533&highlight=
 
astouffer

astouffer

Member
Joined 2004
I recalled seing an amplifier schematic a long long time ago that tied G1 and G2 together through a resistor. This was called a "high mu triode connection" and I believe that it used an 807 or 6L6 type tube. I mentioned this in that previous thread and someone posted that schematic, so this has been done before.
Click to expand...

Its from an old ARRL handbook. 807s were used with a drive transformer and I think they were running near or at class B. They claimed like 120 watts output...

Reminds me of VTL saying they could get 50 watts from a pair of triode strapped 807s :hot:
 
korneluk

korneluk

Member
Joined 2005
George,

Thanks for the thread - I can now use those 46s to drive my next amp...

84042.GIF


Sakuma RCA-46 / RCA-801A parallel SE power amplifier
http://www10.big.or.jp/~dh/work/84042.html


Happy new 2009,
 
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