Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on April 20, 2013, 08:21:42 am

Title: There is a tube with 1/2 12ax7 + ef86 in the same envelope ?
Post by: kagliostro on April 20, 2013, 08:21:42 am

Few time ago this question was posted on an australian forum

I would like to here also the opinion of the members of el34world

about the existence of a tube that contains in the same envelope 1/2 12ax7 + an ef86

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=12AX7 (http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=12AX7)

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6CF8 (http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6CF8)

The tubes that were proposed are 6an8 and 6jn8

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6AN8 (http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6AN8)

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6JN8 (http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6JN8)

What about an what about other candidates ?

Thanks

K

Title: Re: There is a tube with 1/2 12ax7 + ef86 in the same envelope ?
Post by: sluckey on April 20, 2013, 12:51:14 pm

Sunn used the 6AN8 in many of their tube amps. The triode was the PI and the pentode was a voltage amp just prior to the PI. They also used a 7199 in the exact same circuit for some other amps. Pin out is different for the tubes.

Ampeg also used the 7199  as the PI in the Gemini series amps, maybe others too.

I don't know how either 7199 or 6AN8 may compare to 12AX7 or EF86. Probably worth experimenting. I've never actually seen either 7199 or 6AN8 used in a preamp circuit, but the RCA Receiving Tube manuals (for sure RC-23) show a 7199 in a phono ceramic cartridge pickup and also as a PI in several hi-fi power amps. You can find the RCA manuals online if you don't have a paper copy.

Title: Re: There is a tube with 1/2 12ax7 + ef86 in the same envelope ?
Post by: TIMBO on April 20, 2013, 01:37:12 pm

Hi K, I can't comment on how close these tubes are to an EF86 but it seems that Gar (Garnet Amps) liked these tubes in his amps http://www.el34world.com/Forum/index.php?topic=13990.0 (http://www.el34world.com/Forum/index.php?topic=13990.0)

He also liked the 6JW8.  :icon_biggrin:

Title: Re: There is a tube with 1/2 12ax7 + ef86 in the same envelope ?
Post by: kagliostro on April 20, 2013, 07:37:44 pm

Thanks Sluckey & TIMBO

I've also seen the ecf80 (6bl8) tube but I'm not able to evaluate it

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6BL8 (http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6BL8)

K

Title: Re: There is a tube with 1/2 12ax7 + ef86 in the same envelope ?
Post by: PRR on April 20, 2013, 08:40:22 pm

The tri-side of most pent-triodes is 12AU7 like, not 12AX7 like.

That much gain in one small inch would be dangerous.

Title: Re: There is a tube with 1/2 12ax7 + ef86 in the same envelope ?
Post by: kagliostro on April 21, 2013, 02:36:25 am

Actually, even if I'm not so expert to understand completely the datasheet

I can see that those tubes (6an8 - ecf80 - 6jn8) are indicated as Medium-Mu Triode - Sharp-Cutoff Pentode

and 12ax7 is a High-MU Triode

searching I've find this

6as11 - 6bd11 - 6m11 are High-Mu Twin Triode - Sharp-Cutoff Pentode

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6AS11 (http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6AS11)

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6BD11 (http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6BD11)

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6M11 (http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6M11)

but I'm not sure the pentode section of this tubes is comparable to an ef86 tube

there is also one other interesting tube

6mf8 High-Mu Triode - Beam Power Tube

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6MF8 (http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6MF8)

I've only seen schematics where the pentode of a 6af11 Twin Triode - Sharp-Cutoff Pentode

was used as power tube in a small amp

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6AF11 (http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6AF11)

not as preamp tube, and also if I know that someone has used el84 as preamp tube I can't say if between the pentodes on this compactrons and the ef86 there is a large or small difference

K

Title: Re: There is a tube with 1/2 12ax7 + ef86 in the same envelope ?
Post by: DummyLoad on April 21, 2013, 11:02:45 am

there is also one other interesting tube  6mf8 High-Mu Triode - Beam Power Tube

i have a few of those. looks like they are built similar to 1/2 of 12AT7 and a 6HE5 in same envelope. 6MF8 is also similar to the 6LU8. i have a small stash of both and are in my amp cookbook.

on another footnote: the 6DT6A looks promising as 5879 sub in a 6AU6 like equipped ckts. (actually, g3 and k are swapped but usually for audio that's moot).

--pete

Title: Re: There is a tube with 1/2 12ax7 + ef86 in the same envelope ?
Post by: kagliostro on April 21, 2013, 02:28:39 pm

Thanks for the info Pete

Franco