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    6AN8A to replace 7199

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    johns2462

    Posts : 4
    Join date : 2011-10-05

    6AN8A to replace 7199

    Post by johns2462 on Tue Dec 06, 2011 10:46 am

    Hi everyone,

    I have quite a horde of 6an8a tubes bought for my MarkII amps. I reciently aquired a nice ST70 with no tubes and would like to rewire the PC3 to accept the 6an8a tubes I have on hand. Can anyone point me to some nice instructions on how to do this? Once I have vetted that the amp works and determine if I like the sound of the 6an8 tubes I can decide what upgrades/cards to install.

    Thanks in advance, John

    GP49

    Posts : 717
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: 6AN8A to replace 7199

    Post by GP49 on Tue Dec 06, 2011 12:29 pm

    I wrote this for another site in a discussion about the stock Dynaco Stereo 70, about a listener test done years
    ago to rank replacements for the out-of-production 7199 tube. Perhaps it would be of interest here. Note that the
    target audience wasn't as well-versed in tube amplification as is the typical person here at the Dynaco Tube Audio
    forum.

    > 7199 tubes are difficult to source, having been discontinued for many
    > years. The Russian "7199" that was produced a short time ago was
    > not a true 7199; it was apparently a re-pinning of a pentode/triode
    > type that was originally designed for some other use rather than
    > being optimized for audio. In an audio society listening test
    > several years back in the SF Bay Area, substitutes for the 7199 were
    > compared using socket adapters to quickly change between them, as the
    > 7199 has a unique pinout. The 6AN8A was statistically indiscernible,
    > which to some was not a surprise as Dynaco itself used it in the Mark
    > III and Mark II. A few listening tests had the 7199 as more
    > preferred by one listener, which was not enough to be significant.
    > The 7199 was preferred over the 6GH8 by a statistically significant
    > margin. Surprisingly the tube that was MOST preferred was a
    > "ringer", the 5AN8. Specifications of the 5AN8 are identical to
    > those of the 6AN8 but it has a five-volt filament instead of a
    > six-volt filament. In the ST-70 the 5AN8 filament is overvoltaged
    > and the tube would have a short life; what this indicated to me was
    > that the higher emission from overvoltaging the tube's filament was
    > making the driver/inverter stage a bit less "overtasked," as some put
    > it. One or two people who had converted their ST-70s to
    > solid-stage rectification, then took the unused five-volt filament
    > source and used it to run a 5AN8; I never heard what
    > results they got.

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: 6AN8A to replace 7199

    Post by Bob Latino on Tue Dec 06, 2011 6:39 pm

    Pins 1 and 4 and 5 are the same on both tubes (7199 and 6AN8)

    If you want to do the conversion then change the following ..

    The wire/circuit trace that now goes to pin 2 on the 7199 should now connect to pin 6 on a 6AN8
    The wire/circuit trace that now goes to pin 3 on the 7199 should now connect to pin 7 on a 6AN8
    The wire/circuit trace that now goes to pin 6 on the 7199 should now connect to pin 9 on a 6AN8
    The wire/circuit trace that now goes to pin 7 on the 7199 should now connect to pin 8 on a 6AN8
    The wire/circuit trace that now goes to pin 8 on the 7199 should now connect to pin 3 on a 6AN8
    The wire/circuit trace that now goes to pin 9 on the 7199 should now connect to pin 2 on a 6AN8

    Personally, I would not do this because, although the 7199 (IMHO) is not the best driver tube, a 6AN8 is maybe even a step lower in sound quality. I do understand that you have many 6AN8 tubes but even so I would pull the board and switch to the VTA Mark III board where you can use the more common (and inexpensive) 12AT7 driver tubes (if you have the the standard gain Mark III driver board) or 12BH7 driver tubes (if you have the lower gain VTA Mark III driver).

    Bob

    denny9167

    Posts : 152
    Join date : 2011-05-09
    Age : 49
    Location : Texas

    Re: 6AN8A to replace 7199

    Post by denny9167 on Tue Dec 06, 2011 6:44 pm

    GP49 wrote:I wrote this for another site in a discussion about the stock Dynaco Stereo 70, about a listener test done years
    ago to rank replacements for the out-of-production 7199 tube. Perhaps it would be of interest here. Note that the
    target audience wasn't as well-versed in tube amplification as is the typical person here at the Dynaco Tube Audio
    forum.

    > 7199 tubes are difficult to source, having been discontinued for many
    > years. The Russian "7199" that was produced a short time ago was
    > not a true 7199; it was apparently a re-pinning of a pentode/triode
    > type that was originally designed for some other use rather than
    > being optimized for audio. In an audio society listening test
    > several years back in the SF Bay Area, substitutes for the 7199 were
    > compared using socket adapters to quickly change between them, as the
    > 7199 has a unique pinout. The 6AN8A was statistically indiscernible,
    > which to some was not a surprise as Dynaco itself used it in the Mark
    > III and Mark II. A few listening tests had the 7199 as more
    > preferred by one listener, which was not enough to be significant.
    > The 7199 was preferred over the 6GH8 by a statistically significant
    > margin. Surprisingly the tube that was MOST preferred was a
    > "ringer", the 5AN8. Specifications of the 5AN8 are identical to
    > those of the 6AN8 but it has a five-volt filament instead of a
    > six-volt filament. In the ST-70 the 5AN8 filament is overvoltaged
    > and the tube would have a short life; what this indicated to me was
    > that the higher emission from overvoltaging the tube's filament was
    > making the driver/inverter stage a bit less "overtasked," as some put
    > it. One or two people who had converted their ST-70s to
    > solid-stage rectification, then took the unused five-volt filament
    > source and used it to run a 5AN8; I never heard what
    > results they got.

    I did some listening tests in my Mark IV's using a 6BL8 with really good results,I think it's sound is slightly better than the 6GH8,but I'm still doing tube rolling listening tests with the 6GH8.

    Jim McShane

    Posts : 154
    Join date : 2011-10-19
    Location : South Suburban Chicago

    Re: 6AN8A to replace 7199

    Post by Jim McShane on Tue Dec 13, 2011 10:57 am

    Hi John,

    If you have a basket load of 6AN8s then treat them well! The 6AN8/6AN8A is getting harder and harder to find, and the prices are climbing steadily. I agree with Bob L., switch to the board using readily available tubes! Besides, the 12AT7 is a particularly good choice for a push-pull amp.

    Jbacik

    Posts : 1
    Join date : 2012-07-14

    RE 6AN8a for the ST-70

    Post by Jbacik on Sat Jul 14, 2012 3:13 pm

    johns2462 wrote:Hi everyone,

    I have quite a horde of 6an8a tubes bought for my MarkII amps. I reciently aquired a nice ST70 with no tubes and would like to rewire the PC3 to accept the 6an8a tubes I have on hand. Can anyone point me to some nice instructions on how to do this? Once I have vetted that the amp works and determine if I like the sound of the 6an8 tubes I can decide what upgrades/cards to install.

    Thanks in advance, John

    I have to disagree with not using the 6GH8a tube in place of the 7199. I have been using the 6GH8a tube for over 5 years to replace the 7199. The 6GH8a tubes I acquired were manufactured in Japan and sounded so good that they are all I use. I developed the 6GH8a to 7199 adapter as there were none out there after doing an exhaustive search 6 or 7 years ago. Once I came up with a suitable adapter, I put them out there for others as an alternative. There are only three pinout changes from the 7199 to the 6GH8a. I have also substituted the 6AN8 with the 6GH8a but found little difference in sound quality as the characteristics are very similar. This tube makes the ST-70 brilliant and you get to keep the original circuit. I have rebuilt more than 10 of these amps over the years and they all sounded great. I am sure that replacement boards sound great as well due to the feedback I have read on them. I have not tried any myself though. The original sounds great to my ears with the 6GH8a tube. I also now use a bandwidth filter at the input as this has proven to take away transformer saturation at low frequencies at higher volumes. No more muddy sound at all. I do have a great respect for Bob, Joe, and Frank as they have helped me greatly over the years. This response is IMHO only but may help others that are looking for a simple alternative. Regards, Jamey. Cool

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