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

jon_010101 · 14th April 2009, 04:38 AM

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 · 14th April 2009, 04:48 AM

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

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

ErikdeBest · 14th April 2009, 07:19 AM

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 · 14th April 2009, 07:30 AM

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

azazello · 14th April 2009, 07:36 AM

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 · 14th April 2009, 10:48 AM

Quote:

Originally posted by ErikdeBest
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 · 14th April 2009, 11:51 AM

Quote:

Originally posted by 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

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 · 14th April 2009, 12:23 PM

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

jon_010101 · 14th April 2009, 06:23 PM

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

Quote:

Originally posted by Bandersnatch

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

)

Quote:

Originally posted by Tom Bavis
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 · 14th April 2009, 07:33 PM

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

www.esrcvacuumtubes.com

www.vacuumtubes.net

14th April 2009, 04:38 AM	#1
jon_010101 diyAudio Member Join Date: Nov 2005	Seeking Pentode-Triode with a 12AX7 half... 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

14th April 2009, 07:19 AM	#3
ErikdeBest diyAudio Member Join Date: Mar 2003 Location: Itoculo	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. __________________ my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!

14th April 2009, 07:30 AM	#4
revintage diyAudio Member Join Date: May 2007 Location: Eskilstuna, Sweden	6F12P, triode mu=100 Gm=20(instead of the wimpy 1,6mA/V), pentode Gm=20. __________________ Brgds Lars

14th April 2009, 07:33 PM	#10
tubelab.com diyAudio Member Join Date: Jul 2005 Location: South Florida	The 6LY8 and 6JT8 are on sale for $1 each at these two places : www.esrcvacuumtubes.com www.vacuumtubes.net __________________ Too much power is almost enough! Turn it up till it explodes - then back up just a little.

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14th April 2009, 04:48 AM	#2
jon_010101 diyAudio Member Join Date: Nov 2005	Hmmm... 6CM8 has promise, but the search continues... 6KT8... really nice curves... slightly high gm...

14th April 2009, 07:36 AM	#5
azazello diyAudio Member Join Date: Aug 2008 Location: Bulgaria	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 !

14th April 2009, 12:23 PM	#8
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	How about 6EB8, 6GN8, 6LY8, 6JT8 - all have the same footprint as 6AW8.

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