Triodes with an extra grid

[jlsem]

I have a few triodes that appear to have more than one grid, namely 6AC5GT, 1635 (a special 6N7) and 7236 (a computer rated 6AS7 type). Does anyone know what is the reason for the extra element?

John

 

[Sch3mat1c]

http://www.mif.pg.gda.pl/homepages/frank/sheets/049/6/6AC5GT.pdf
6AC5 appears to be a normal triode with extremely low perveance, but high mu (125!) and plate resistance. Like a heavy plate 12AX7 I guess...

http://www.mif.pg.gda.pl/homepages/frank/sheets/049/1/1635.pdf
1635 looks like a dual (common cathode) version of 6AC5 or 6N7 as you say. I think 6N7 is more like a 1/3-current 6SN7 though; this is closer to 12AX7 in current.

http://www.mif.pg.gda.pl/homepages/frank/sheets/127/7/7236.pdf
Looks like no more than a 6080 or 6AS7GB to me.

You're probably seeing two seperate or mostly seperate units in one, not multiple grids to one "triode". Wait'll you see a heptode or triple triode (like 6T10(?)).

Tim

 

[jlsem]

You're probably seeing two seperate or mostly seperate units in one, not multiple grids to one "triode". Wait'll you see a heptode or triple triode (like 6T10(?)).

I assure you that there are two grids on these triodes. On the 6AC5GT, they are tied together, one being wound much more coarsely than the other. If memory serves, the extra grid on the 7236 is tied to the plate. Not as radical as the 6C5 which is a pentode internally strapped as a triode, but interesting enough to take note.

John

 

[fdegrove]

Hi,

I assure you that there are two grids on these triodes.

Sure can't see them on the data sheets...Any idea what purpose they'd serve?

I'm well aware that tubes like that exist (and I don't mean penthodes etc.) but they're usually special purpose and you'd see that extra grid shown in the datasheet.

With the references given in your post these extra grids just can't get accessed from the outside so, I wonder what they'd be used for??

Cheers,😉

 

[Sch3mat1c]

I assure you that there are two grids on these triodes. On the 6AC5GT, they are tied together, one being wound much more coarsely than the other. If memory serves, the extra grid on the 7236 is tied to the plate. Not as radical as the 6C5 which is a pentode internally strapped as a triode, but interesting enough to take note.

John

Hmm... well that's a corker! I've never seen those tubes before, just as Frank says. Can you photograph them?