Seeking Pentode-Triode with a 12AX7 half...

[jon_010101]

I am looking for a pentode-triode where half is basically a 12AX7 (similar gm, gain 70-100).

Some nice higher-gm options exist (6AW8A), but low idle current would be preferable here.

Pentode should be high-ish gm, to be used as a CCS at ~8-10mA for another stage's differential amp tail. 6GW8 is overkill 😉

It seems that this should be easy, but I have yet to find one

 

[jon_010101]

Hmmm... 6CM8 has promise, but the search continues...

6KT8... really nice curves... slightly high gm...

 

[ErikdeBest]

The ECL86 is said to contain a 12AX7 triode and a (derated) EL84 pentode. GM of the pentode is 10mA/V when operated at 36mA...probably less when operated at the desired 8-10mA.

 

[revintage]

6F12P, triode mu=100 Gm=20(instead of the wimpy 1,6mA/V), pentode Gm=20.

 

[azazello]

I like the axiome - more current - better sound !
I prefer You 6LR8 very linear tube for TV - Ia triod - 6-8 ma and Ia pentod - 55-60 ma.
I have apl. with 6LR8 and sound is very nice !

 

[richwalters]

The ECL86 xxxxxxxx.

I tried a tempting design around this, but this tube is now getting rare and NOS expensive. The far cheaper PCL86 with a 14 V heater may be an alternative solution. Not sure of US equiv.

richy

 

[Bandersnatch]

I am looking for a pentode-triode where half is basically a 12AX7 (similar gm, gain 70-100).

Some nice higher-gm options exist (6AW8A), but low idle current would be preferable here.

Pentode should be high-ish gm, to be used as a CCS at ~8-10mA for another stage's differential amp tail. 6GW8 is overkill 😉

It seems that this should be easy, but I have yet to find one

Questions:
Do you need 12AX7 gain?
How much headroom is available for the pentode section CCS? If you're direct-coupled( the SE gain stage plate voltage setting this qty).
cheers,
Douglas

 

[Tom Bavis]

How about 6EB8, 6GN8, 6LY8, 6JT8 - all have the same footprint as 6AW8.

 

[jon_010101]

Re: Re: Seeking Pentode-Triode with a 12AX7 half...

I see many have recommended tubes that are way too serious for the intended application, but I will keep them in mind for future purposes 😀

Questions:
Do you need 12AX7 gain?
How much headroom is available for the pentode section CCS? If you're direct-coupled( the SE gain stage plate voltage setting this qty).

Gain of 70-100 with gm<2000 would be ideal, and 150V realistically available for the pentode. Must be 9-pin, reasonable 6.3V or tapped 12.6V filament. (BTW, just replied to your reply in another forum 😉)

How about 6EB8, 6GN8, 6LY8, 6JT8 - all have the same footprint as 6AW8.

Interesting - I will investigate! Friends of the 6AW8 are friends of mine!

 

[Tubelab_com]

The 6LY8 and 6JT8 are on sale for $1 each at these two places :

www.esrcvacuumtubes.com

www.vacuumtubes.net

 

[ErikdeBest]

another triode pentode combi with the same pinout is the 6KR8, available from www.vacuumtubes.net This one spots high transconductance on both units, if memory serves me well about 20mA/V.

Edit: I was wrong: the pentode has 20mA/V (with ~20mA current), the triode achieves about 10mA/V with 15mA current.

 

[jon_010101]

Excellent! Thanks!

Looks like we have a winner with 6LY8 - high gm pentode, low gm triode that looks very 12AX7y. If it ends up being funky, switch to 6AW8 is just a few resistors away.

 

[smoking-amp]

6MV8 same footprint as 6AW8, has Mu 100, gm 4000, 1 Watt, on sale for $1 too. with 2.5 W pentode with Gm 9000

7716 same footprint as 6AW8, has Mu 102, gm 2900 1 Watt $4
with 5W pentode with Gm 10,000