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    Driver tubes



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    Driver tubes

    Post by corndog71 on Tue Jan 28, 2014 1:46 pm

    Is there any preference for the three driver tubes in the ST120? In other words, do they need any special attention as far as matching or low noise? I see the center tube is used for both channels. Would it be ideal for the best possible sound to have matching triodes there? I know some people don't pay attention to this sort of thing but I want to get the best performance possible.

    I'm more than halfway finished building my ST120. Getting pretty excited here.  bounce cyclops 

    Bob Latino

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    Re: Driver tubes

    Post by Bob Latino on Tue Jan 28, 2014 2:44 pm

    Actually any 12AU7, 12BH7, 5814, 5963 or 6189 driver tube may be used in any of the three driver positions. The CENTER driver tube is the initial voltage amplifier for BOTH channels. I would not say that matched triode sections are absolutely essential on any of the three driver tubes - BUT - if you are going to match any sections in any of the driver tubes then do it on the center tube. The center tube has the most influence of the three on the sound of the amp. If you want to "roll" driver tubes in and out to see the change on the sound, I would just roll in different center tubes.

    Some of the best driver tubes I have listened to are the USA made 5814 and 5963 tubes. I recently acquired a good supply of USA made Sylvania and RCA 5963 driver tubes from a friend who deals in tubes. The VTA amp kit customers who order a VTA ST-70 or ST-120 kit with a tube set get USA made RCA or Sylvania 5963 driver tubes shipped with their kit. I test each one and have found the two triode sections on these 5963 tubes to match pretty close. Of the currently made 12AU7 or 12BH7 tubes, the Russian ElectroHarmonix are also pretty good.



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    Re: Driver tubes

    Post by skriefal on Wed Jan 29, 2014 1:47 am

    The problem with 5963s is that many of them are highly microphonic.  At least most that I've encountered have been. If you're buying untested tubes then it's best to stick with 5814s or organ-labeled 12AU7s.  If you're buying tubes that are pre-tested for microphonics, however, then this shouldn't be a concern.


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    Re: Driver tubes

    Post by sKiZo on Wed Jan 29, 2014 6:54 pm

    Lot of people put rubbers on their tubes before using them ...

    (Probably a better way to put that)  geek 

    Military grade will usually have the extras that eliminate microphonics. Heavier structure, extra mica, spring loading, etc.

    Hadn't really thought about organ tubes as being better in that regard though. Seems reasonable as the lower registers from the big guns could definitely be considered hostile.

    As far as what works best, it makes sense to have a well balanced tube in the center, but that's only part of the equation. I'm still playing with combinations - currently using a 1940's RCA triode balanced foil getter 12AU7 in the middle and Sylvania 12BH7a's in the channels. Got plenty other options in my big box o'tubes, but those play well together.

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