7199 vs 6U8
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kvflyer
Super Member
It will save a lot of money. But since the ST70 has a circuit board, it will be difficult to do that swap. On a point-to-point construction, you only have a few wires to move. There are adapters out there if you are into it. I have seen ones for changing the 7199 to a 6GH8...
kvflyer
Super Member
Sorry for the misunderstanding. I have not done it yet because so far, I have just enough 7199s to fill the sockets. But remember that HH Scott had any of those combinations in their amplifiers. My guess would be that as long as the circuit change for the different pin-out should also match circuit for the "new" tube. For instance, if resistor values are different, then they should be changed as well. Then, I would bet you would be good to go.
BinaryMike
Pelagic EE
Here's one useful resource: http://www.audioregenesis.com/products/SCA-35/images/6gh8a_tubes.PDF Now-dead link
Possible alternative: http://tronola.com/6gh8a_tubes.pdf
Possible alternative: http://tronola.com/6gh8a_tubes.pdf
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Is it a direct 6U8/6GH8 sub? For some reason, I've recently fallen into piles of 6U8 and 6GH8 tubes, including some interesting Euro valves.
interesting question, no experience personally however.
kvflyer
Super Member
It certainly makes sense to change the wiring of a point-to-point type of amp to use the 6GH8 tube. Some RCA vacuum tube color sets used a bunch of them and ran them on the ragged edge. They were common failures so the tube manufacturers pumped them out to satisfy the demand. Since I have a couple of RCA color sets, I went hunting for sleeves of them and found them on the auction site for cheap. It was found that the RCA manufactured 6GH8 did not hold up as well as the Sylvania manufactured version. So, the last sleeve of RCA labeled 6GH8 tubes were actually made by Sylvania! I would encourage anyone with this issue with a 7199 to at least consider this "rewire". Somewhere, I have a point-to-point document that shows essentially the same thing as the PC board modification listed above...
kvflyer
Super Member
Here is an example of the conversion from 7199 to a 6U8 complements of the Tubedepot. The pin-out between the 6U8 and 6GH8 is the same, 9AE so if you follow up with any changes (if necessary) in component values is followed, you may be good to go. Remember that although this document below shows a 6U8, it is the same PIN-OUT as a 6GH8.
http://site.tubedepot.com/pdf/7199_6u8.pdf
http://site.tubedepot.com/pdf/7199_6u8.pdf
jaymanaa
RIP 1961-2018
Please let us know, I've done very little experimenting with these tubes and am very curious as to what your impressions are. Thanks, jay
6GH8A is a pretty good sounding tube, especially the Amperex ones I've heard. I have never heard a good sounding 6U8 IMO. If I was doing this, I'd go with the 6BL8 like Keg suggests. Mainly because keg does a lot of experimenting and knows what sounds good.
Ever heard a Telefunken 6U8? I have at least one floating around here.
sheltie dave
Addicted Member
Sam, the Scott 299D I have had Tele 6U8s.
Speaking of which, I found a 6BL8 stashed around here for that Scott LT-110 tuner.
GreatTone
Super Member
Shortly after I got my Dynaco SCA-35, I replaced the power amp boards, which included a change from 7199 to 6GH8A/6U8A. It sounded better after the switch, but that may have been because of all the new components in the boards. I certainly don't feel there's anything lacking, as it sounds very, very good. I started out with Raytheon 6GH8As, but after only a year, one started squealing. So I tried JAN Philips 6U8As, which is what I have in there now. If anything, the 6U8As sound better. However I haven't heard enough to make a judgement, but am very happy with these current 6U8As. I'll probably stick with those if/when I need new ones.
