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Old 14th April 2009, 04:38 AM   #1
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Default 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
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Old 14th April 2009, 04:48 AM   #2
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Hmmm... 6CM8 has promise, but the search continues...

6KT8... really nice curves... slightly high gm...
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Old 14th April 2009, 07:19 AM   #3
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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.
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Old 14th April 2009, 07:30 AM   #4
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6F12P, triode mu=100 Gm=20(instead of the wimpy 1,6mA/V), pentode Gm=20.
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Old 14th April 2009, 07:36 AM   #5
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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 !
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Old 14th April 2009, 10:48 AM   #6
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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
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Old 14th April 2009, 11:51 AM   #7
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Default Re: Seeking Pentode-Triode with a 12AX7 half...

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
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Old 14th April 2009, 12:23 PM   #8
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How about 6EB8, 6GN8, 6LY8, 6JT8 - all have the same footprint as 6AW8.
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Old 14th April 2009, 06:23 PM   #9
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Default 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

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!
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Old 14th April 2009, 07:33 PM   #10
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The 6LY8 and 6JT8 are on sale for $1 each at these two places :

www.esrcvacuumtubes.com

www.vacuumtubes.net
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