There's so much spam and hate here I thought I'd conduct a quick pole.

I've seen schematics of EF86 signal pentodes wired as triodes by simply
tying grids 2 and 3 to the plate without resisters. I've also seen one
where grid 3 was tied to the cathode but grid 2 was tied to the plate,
maybe through as resister. Then there's something I read in Kevin
O'Conner's books about EL34's with grid 3 tied to a negative bias. I've
never tried any of these, yet, But I'm building a Dynaco ST70 with EF86
- 12AU7 - EL34's, (EF86 and EL34 wired as triodes) and I'd like some
opinions from people with more experience.

So here's the pole, for each tube:

grid 3: plate, cathode, ground or negative bias?
Resister or not?
Would a negative bias do anything for the EF86?

grid 2: plate thru resister or not?

Thanks.

Karl wrote:

There's so much spam and hate here I thought I'd conduct a quick pole.

I've seen schematics of EF86 signal pentodes wired as triodes by simply
tying grids 2 and 3 to the plate without resisters. I've also seen one
where grid 3 was tied to the cathode but grid 2 was tied to the plate,
maybe through as resister. Then there's something I read in Kevin
O'Conner's books about EL34's with grid 3 tied to a negative bias. I've
never tried any of these, yet, But I'm building a Dynaco ST70 with EF86
- 12AU7 - EL34's, (EF86 and EL34 wired as triodes) and I'd like some
opinions from people with more experience.

So here's the pole, for each tube:

grid 3: plate, cathode, ground or negative bias?
Resister or not?

G3 can be taken to the cathode on the socket.
This will supress secondary anode emission and minimise
G2 current even though you will have G2 connected to the anode
directly or via a 220 ohm R.

Its not a critical issue, and G2 and G3 may both be directly connected to
the anode with no R because the tube is operating at very low power
and G2 dissipation amounts are well below the maximum rating no matter how
you
connect the tube.

Connecting EF86 G3 to either 0V or to the anode when triode operation
is used will make little difference to the triode operation.



Would a negative bias do anything for the EF86?

No. G3 is usually connected to the cathode, since anything
at or a little below cathode potential is OK for suppression purposes
which are really only required for pentode operation.



grid 2: plate thru resister or not?

220 ohms is OK, and used to stop oscillations which are unlikely.
The 220 ohms won't change the triode operation at all.

Patrick Turner.



Thanks.

Patrick Turner wrote:
Karl wrote:

There's so much spam and hate here I thought I'd conduct a quick
pole.

I've seen schematics of EF86 signal pentodes wired as triodes by
simply
tying grids 2 and 3 to the plate without resisters. I've also seen
one
where grid 3 was tied to the cathode but grid 2 was tied to the
plate,
maybe through as resister. Then there's something I read in Kevin
O'Conner's books about EL34's with grid 3 tied to a negative bias.
I've
never tried any of these, yet, But I'm building a Dynaco ST70 with
EF86
- 12AU7 - EL34's, (EF86 and EL34 wired as triodes) and I'd like
some
opinions from people with more experience.

So here's the pole, for each tube:

grid 3: plate, cathode, ground or negative bias?
Resister or not?

G3 can be taken to the cathode on the socket.
This will supress secondary anode emission and minimise
G2 current even though you will have G2 connected to the anode
directly or via a 220 ohm R.

Its not a critical issue, and G2 and G3 may both be directly
connected to
the anode with no R because the tube is operating at very low power
and G2 dissipation amounts are well below the maximum rating no
matter how
you
connect the tube.

Connecting EF86 G3 to either 0V or to the anode when triode operation
is used will make little difference to the triode operation.



Would a negative bias do anything for the EF86?

No. G3 is usually connected to the cathode, since anything
at or a little below cathode potential is OK for suppression purposes
which are really only required for pentode operation.



grid 2: plate thru resister or not?

220 ohms is OK, and used to stop oscillations which are unlikely.
The 220 ohms won't change the triode operation at all.

Patrick Turner.



Thanks.


Thanks for the response, Pat. I thought I'd get more responses than
just one, but I guess the answer is pretty simple. BTW I like the site
you put up.