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    7199 vs 6gh8 vs 12au7 vs 6sn7 for st70 ????

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    wantech

    Posts : 6
    Join date : 2017-09-26

    7199 vs 6gh8 vs 12au7 vs 6sn7 for st70 ????

    Post by wantech on Thu Oct 12, 2017 12:43 pm

    Thinking of replacing the pc board on my st70, learn that there are many different one

    would like to know which one will be better.... the best......

    7199 vs 6gh8 vs 12au7 vs 6sn7

    thanks
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    Bob Latino
    Admin

    Posts : 2567
    Join date : 2008-11-26
    Location : Massachusetts

    Re: 7199 vs 6gh8 vs 12au7 vs 6sn7 for st70 ????

    Post by Bob Latino on Thu Oct 12, 2017 1:22 pm

    wantech wrote:Thinking of replacing the pc board on my st70, learn that there are many different one

    would like to know which one will be better.... the best......

    7199 vs 6gh8 vs 12au7 vs 6sn7

    thanks

    Just my opinion but with a STOCK Dynaco ST-70 I would get a new VTA driver board that uses 12AU7 driver tubes. 7199 driver tubes are not made anymore and tend to be expensive now. Yes, you can use a 7199 to 6GH8 adapter on the stock driver board and use the less expensive 6GH8 driver tubes.

    12AU7 and 6SN7 tubes have basically the same characteristics but a 12AU7 is a noval (9 pin) tube and a 6SN7 is an octal (8 pin) tube. Consider these two reasons to favor the 12AU7 board.

    1. 6SN7 tubes draw double the current of a 12AU7 (6SN7 = .6 amps per tube and 12AU7 tubes = .3 amps per tube) Multiply this by the 3 tubes on the driver board (.3 amps X 3) and you get .9 amps extra current draw from the 6SN7 board from a STOCK Dynaco PA-060 power transformer that already runs hot and is already marginal with its ability to provide current for the amp. With three 6SN7's in there, the amp will run even hotter.

    2. 12AU7 tubes are more plentiful and cheaper to buy. There are still many USA made 12AU7 tubes out there. You can also use the military industrial versions of the 12AU7 the 5963, 5814 and 6189. You can also use the 12BH7 on the VTA noval board. USA made 6SN7 tubes tend to be more expensive.

    Some who have the 6SN7 octal version of the VTA driver board will say "it sounds better" but personally I don't hear it ? Large USA manufacturers of tube amps like McIntosh and Conrad Johnson have never used octal driver tubes. A few years back McIntosh came out with their new statement tube amp - the 300 watt MC2301 monoblock amps. These amps are $22,000 a pair. At that price they could have chosen ANY driver circuit/driver tube for "best sound". Each MC2301 amp uses two 12AT7 (noval - 9 pin) driver tubes.

    Bob
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    Peter W.

    Posts : 502
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: 7199 vs 6gh8 vs 12au7 vs 6sn7 for st70 ????

    Post by Peter W. on Thu Oct 12, 2017 1:34 pm

    Opinion Here:

    a) The 7199 is a triode/pentode - a bit more refined and a bit more complex than the two dual triode options.
    b) Whereas the Russians were making them briefly (and, typically, not very well), they are no longer. Meaning that *new* replacements are not available at the present moment.
    c) There were many thousands of them made, and they were used in many different amps from many different manufacturers. So the expectation is that they will remain available - albeit at an increasing cost - into the foreseeable future.
    d) A great many of these tubes are either microphonic, or distort to a greater-or-lesser degree depending on use and age.

    Cutting to the chase: If you have a good supply of 7199s in good condition that are neither microphonic nor distorting, it is my opinion that they are superior to the dual-triode options, if only just. You also have one less filament than with a three-tube configuration and far less current used than with an octal configuration.

    Now, moving on to the 6GH8 - another 'orphan' tube to my knowledge, but one that enjoyed much higher production back in the day, and so might be easier to find and at a better price. I am told (and my one example using same does not refute or support) that the 6GH8 has fewer problems than the 7199.

    Writing for myself - I have a lifetime supply of NIB/NOS RCA-branded 7199s (6), and three amps presently in operation that use them. In my case, I would therefore stick with the 7199s. As well, adapter plugs are available off-the-shelf to convert a 7199 board to 6GH8 use, meaning I am covered either way. In any case, with my vintage amps, I *would not* go with the octal option.

    Were I to advise in a vacuum, I would, in rank order: 1. 6GH8. 2. 7199. 3. 12XX7 x 3. 4. Any Octal option.

    Others will have different thoughts and advice - I am sure well, supported.

    eickmewg

    Posts : 74
    Join date : 2014-08-29

    Re: 7199 vs 6gh8 vs 12au7 vs 6sn7 for st70 ????

    Post by eickmewg on Thu Oct 12, 2017 3:41 pm

    There are highly regarded tube preamplifiers, e.g. Icon Audio, Cary, etc., that use 6SN7 tubes.  I am using a Black Treasure CV181 Z in the amplification position and, while an expensive tube, far exceeded a Platinum Mullard 12AU7-type tube, which was just about as expensive.  Maybe for an ST70, with original power transformer, octals aren't appropriate, but that is an amp-related and not a tube-related issue.

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