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6EJ7 or 6EH7 triode strapped?

Kegger

Kegger

R.I.P. 1/12/1966 - 6/1/2017
I am wondering if by chance does anyone have any 6EJ7 or 6EH7 triode data sheets?
I'm really curious about the plate resistance and gain on these tubes strapped in triode.

I have several of these tubes and was thinking of triode strapping them as drivers.
Thanks for anything anyone may want to share on these particular tubes.
 
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Well it looks like the 6EJ7 is around 11k plate resistance and 45 gain, was
hoping for lower on both accounts but info I find says it's a fine audio tube.

EDIT: Look down a bit, the actual curves and info is posted..

I'd imagine the 6EH7 is higher on both accounts, judging by the pentode #'s.
 
Kegger said:
Well it looks like the 6EJ7 is around 11k plate resistance and 45 gain, was
hoping for lower on both accounts but info I find says it's a fine audio tube.

I'd imagine the 6EH7 is higher on both accounts, judging by the pentode #'s.
Click to expand...

Look at the 6EH7 again. It is a variable pitch g1 for variable mu/gm. The EF184/6EJ7 should be a very nice triode, but I am curious about the 11k plate Z. Gm is 15 mA/V so the plate Z should be a lot lower( at advertised current ). Of course at lower current, plate Z goes up, and usually more quickly for triode strapped pentodes v. real triodes.
cheers,
Douglas
 
Also wondering about the 12BY7's #'s with it triode connected.
Looks like an EL84 trioded is pretty close to what I'm looking for as well.

Trying to find something that ends up being 2-4k rp with an mu less then 10.
(In a 9pin) Only true triode I find is the 12B4, I'd like to try others in it's slot.
 
Hey!!!,
If you're hunting mu less than 10, you may wont to consider a real triode instead. 6BX7 comes to mind. Triode strapped 12BY7 has a mu of ~28 or so along with its cousin the 12HL7. 12GN7 has a triode mu colser to 40, but with gm of ~40 mA/V the R_p is quite low.

You could also try a small load, about 30% of R_p to reduce gain. Since output Z is a parallel combination of R_p and plate load, this should yeild a very low number for linestage service.

Try also 6CL6, its triode mu is ~16 and with a low plate load would be easy to drop under 10. I have not found any triode plate curves for that one though...

Just as in the pentode linestage I built, I don't think a lot of damping factor is called for. The load is a light, and mostly resistive. I think the low plate load arena has been labeled 'Off Limits' due to considerations applied to maximum output swing or power applications. I think there is some easy 'low hanging fruit' to be had there.
cheers,
Douglas
cheers,
Douglas
 
Hey Tom thanks for that link,, just the sorta thing I was looking for, anymore
of those around in other places. I see he doesn't do the EL84 but like the EL86.

---------------
Doug and or Tom or anyone else, what I'm trying to do is replace the VA amp
I'm currently using in my amp, which is a 12B4, I'd like to replace it with some
tube that would end up having similar specs, lowish plate resistance plus mu
of less then 10 as I want to use my same circuit but want to keep feedback
low or nothing so I don't want a bunch of gain I have to knock back down a
little or at all with using some kinda feedback. (Experimenting here)

What I've got now is pretty darn good, but I'd like to try some different tube for
the 12B4 as I don't have a ton of space in the amp to do a proper power supply
to feed the 12B4 and was thinking if I could find some funky pentode and wire it
as a triode that I may find what I'm looking for, that EL86 just may be the ticket.

How do I figure the plate resistance for the EL86 from those #'s on Pete's site?
 
mu / gm is plate resistance. So start with the highest transconductance ones... however, transconductance is NOT a constant - it varies with the operating point - a set of curves would be helpful (plate resistance is the slope of the curve at the operating point).
 
Thank you Douglas, And Tom!
Looks like the EL86 may be worth a shot without even changing my 6.8k load resistor.
(I'm sure I'll have to experiment with my cathode,bias resistor which is now 820 ohms)

I see variac coming in handy, AGAIN!
 
Kegger said:
Thank you Douglas, And Tom!
Looks like the EL86 may be worth a shot without even changing my 6.8k load resistor.
(I'm sure I'll have to experiment with my cathode,bias resistor which is now 820 ohms)

I see variac coming in handy, AGAIN!
Click to expand...

I think I would be slowed down more by removing my variac than by removing one of my hands...one should have two for best results of course....:) hands, variacs, soldering irons...
cheers,
Douglas

The EL86 is one neat lookin' tube. I had not thought its triode mu would be so low. I have a few mouldering away in my stash, they just got bumped a notch in value...:)
 
Yes not sure how others get by without the trusty variac, mine is used more
then any other single piece of equipment by far. :D

Yes I'm glad it looks like there is at least one 9pin pentode that when strapped in
triode is in the ballpark of what I was looking for, look hard enough and ye shall find! :D

There's probably others as well, just gotta keep lookin, maybe some of those triode/
pentode jobbies that everyone discards may hold some value after all.:scratch2:
 
Well got the EL86's wired up in the amp.

And while I'm gunna hold back my observations till I get some listening in the
main setup, but let's just say I think this tube just may be worth checkin out!

I'm runnin on a 360v supply, 10k plate load, with an 820ohm cathode resistor.
Which yields, 19ma plate current at 170v on the plates with a neg grid of 16.
Don't know if other operating points would be better or my old tubes but I am
getting some microphonics when I tap em, I'll try some other tubes tommorrow.
 
As there the same pinout and wanted to see how they respond, threw some
EL84's in the circuit (no modifications) and they sound pretty sweet as well.

I get about 240volts on the plates of the EL84's, (both the el86 and el84 in triode)

Went and got some o'rings and others things to tame the microphonic's, it's manigable.

Just FYI for anyone interested.
 
I find any thread about using pentodes as gain stages interesting. Give us a little more skinny. What do you really think? Inquiring minds and all.:scratch2: :D
 
Let me get a bit more listening in and on the main system but I do believe there
is something nice happening here.:thmbsp:

You could even build a pre with these and switch between EL84, EL86 an then you
could even rewire 2 pins to go to the 12B4 without having to change anything else.:smoke:

So far I think I'm liking it quite well, real good bass weight with a light airyness to
the top end that so far I'm finding very engaging.:music:
 
Hey!!!,
Since you're up to a mu of ~20 with the EL84 you might want to consider the 12A4. It is otherwise just like the low mu 12B4 but has a mu of 20. I acquired a small stash of these when I discovered them...:) when next you visit, I'll give you a pair.
cheers,
Douglas
 
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