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    7199 Board to 6GH8 Board Question

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    scsidude2

    Posts: 21
    Join date: 2010-03-19
    Age: 27
    Location: Dekalb, IL

    7199 Board to 6GH8 Board Question

    Post by scsidude2 on Mon Jul 12, 2010 5:06 pm

    I'm replacing the original PC-3 board on one of my ST-70's with one using the 6GH8, they are identical as far as resistor values and caps are concerned but just wanted to make sure there weren't any precautions i should take during the swap. Thanks everyone! -Ryan

    Bob Latino
    Admin

    Posts: 1907
    Join date: 2008-11-26
    Location: Massachusetts

    Re: 7199 Board to 6GH8 Board Question

    Post by Bob Latino on Tue Jul 13, 2010 4:29 am

    scsidude2 wrote:I'm replacing the original PC-3 board on one of my ST-70's with one using the 6GH8, they are identical as far as resistor values and caps are concerned but just wanted to make sure there weren't any precautions i should take during the swap. Thanks everyone! -Ryan

    Hi Ryan,

    The 7199 is basically the same tube as a 6GH8. You won't have to make any resistor or cap changes. Pins 2, 6 and 7, however, have different pin outs from one tube to the other. Below is a diagram of the pin differences between a 7199 and a 7687 which is the same tube as a 6GH8.

    Bob



    GP49

    Posts: 489
    Join date: 2009-04-30

    Re: 7199 Board to 6GH8 Board Question

    Post by GP49 on Tue Jul 13, 2010 10:28 am

    There shouldn't be any compatibility issues at all when changing from a 7199-based board to a 6GH8-based board. Nothing should burn up or blow out.

    Drifting off topic a bit...there is some difference of opinion as to how identical the 7199 and 6GH8 really are, once you get beyond the different pinouts. Some, such as Bob, above; and Frank Van Alstine say that the two tubes are identical, perform the same, and sound the same. Others claim that the 7199, which was specifically designed as an audio tube, is superior in audio applications. That was the original claim when Dynaco used the 7199 in the Stereo 70, while the earlier Mark II and Mark III used the 6AN8 (which has its own pinout different from that of the 7199 and 6GH8). And yet Dynaco continued to use the 6AN8 in the Mark II/III amplifiers to the very end.

    The few 7199 vs. 6GH8 listening tests I've attempted have been inconclusive, and with the ephemeral nature of audio memory, not really to be trusted anyway; they involved listening to the same amplifiers, usually mildly upgraded Stereo 70s, before and after conversion from the 7199, which ranges from expensive to unavailable, to the much more common 6GH8. The time spent making the conversion meant the listening comparisons were done quite some time, in some cases hours apart.

    There do exist plug-in converter sockets for around $20 that will allow quick, direct substitution of the 6GH8 for the 7199, but I haven't used them.

    The actual PEOPLE who made these decisions and did the tube designs, way back when, are by now retired or deceased and there is pitifully little documentation of their work. Current production is no help, either, since the Russians and Chinese will sometimes package the same tube guts with different pinouts and label (and price) them accordingly. I wondered what was going on when the Russian 7199 showed up; to me it didn't SOUND like a genuine, original USA-made 7199.

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