7199 replacement?
- Thread starter MSamia
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6GH8A TO 7199 tube adapters would do it. A pair of adapters would set you back 30 bucks or so. The tubes are still fairly cheap.
Mike
Mike
Dandy
Addicted Member
Unless your original board is in good condition, nicely recapped etc, I agree with bktheking. The modern boards are much better quality and easy to install.
I see the adapters at Triode are just under $25 each, so about $50 for a pair. Or you can rewire your existing board's sockets for 6GH8s.
I see the adapters at Triode are just under $25 each, so about $50 for a pair. Or you can rewire your existing board's sockets for 6GH8s.
TerrySmith
Active Member
What if you made adapters for 6AN8 tubes like a MK-3 uses? I'm kinda surprised no one makes a replacement board using these instead of 6GH8 types.
6AN8 is another dead end - no longer in production, no other tube with the same pin connections. The 6GH8 shares its pinout with 6AX8, 6U8, 6EA8, 6BL8, 6KD8, 6678, 7687, 6HL8, 6LM8, 6LN8, 6KE8, 6LX8, 6JW8, 6MU8... among others. Some of these may need a resistor change or two to give best performance. To a lessor extent, this has always been true with 7199s - different lots of 7199s may show a difference in distortion, which can be minimized by adjusting the value of the screen resistor.
zandru
"Hard At Play"
Good Moring MSmia,
The 6GH8A to 7199 tube socket adapters are less than $30 a pair.
Real NOS 7199's range from $60 (pr) to the absurd.
Quality used 7199's range from $20 (pr) to $60 (pr) and up.
Real NOS 6GH8A's range from $20 (pr) to not much more.
New or Quality used 6GH8A's sell for around $5 and a little more apiece.
The 6GH8A to 7199 tube socket adapters do not require a circuit Mod.
(However; some sympathetic ST-70 tube Gurus will certainly disagree)
It's debatable to weather the 6GH8A is truly and sufficiently able to
fill the shoes and perform like the 7199 does in your ST-70.
My guess is that It's snob appeal in favor of being partial to the 7199.
The 6GH8A to 7199 tube socket adapters are less than $30 a pair.
Real NOS 7199's range from $60 (pr) to the absurd.
Quality used 7199's range from $20 (pr) to $60 (pr) and up.
Real NOS 6GH8A's range from $20 (pr) to not much more.
New or Quality used 6GH8A's sell for around $5 and a little more apiece.
The 6GH8A to 7199 tube socket adapters do not require a circuit Mod.
(However; some sympathetic ST-70 tube Gurus will certainly disagree)
It's debatable to weather the 6GH8A is truly and sufficiently able to
fill the shoes and perform like the 7199 does in your ST-70.
My guess is that It's snob appeal in favor of being partial to the 7199.
Naptown Rob
Ponographer
I run mine with the adapters, & I'm very happy. The right 6gh8a's actually can sound better than 7199's, and as mentioned, can be had quite cheaply - makes for a fun tube roll.
drknstrmyknight
Addicted Member
They last forever, I've got a drawer full of Philips-JAN other NOS 7199 and have never needed one.
You can easily buy replacement ST-70 boards with 6GH8 tubes, on "that auction site" or other locations. It was the standard setup, for the later versions of the ST70, made in the late '70s to the '80s.
That, IMHO, would be the most elegant thing to do. No adapters needed. You know that board will work right, and will sound like the original...
Regards,
Gordon.
That, IMHO, would be the most elegant thing to do. No adapters needed. You know that board will work right, and will sound like the original...
Regards,
Gordon.
Pio1980
AK Member
I used the Vinage Eectron 6GG8 board, and would recommend replacing the 1.5 meg screen resistors with ca 780k- 820k 1/2W metal film resistors to better optimize the phase splitter.
2x’s
Ears for Beers
when someone says better I wonder what that means. I quiet like the sound I’m getting, guessing I’ll like the sound of the 6U8’s asswell, I like different flavors!! What are the differences you heard?
cademan
Lunatic Member
Hmm, drknstrmyknight was last seen in 2019. Be sure to look at the dates of the posts.
Last post in thread was from GordonW in 2012.
You can always PM people and see if they will reply.
By the way, this is all just FYI.
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I did a small evaluation of 7199 replacements in a dynaco sca35 where a small number of tubes were tested.
Two groups of measurement : dist at 1 5 and 15 w output power, and voltages around the phase spiltter where
Va(p) = voltage at penthode plate, Vg2 = voltage at penthode screen and Va(t) voltage at triode plate. These
voltages shows how close the working point is from an ideal cathodyn phase inverter. No components are
changes only the tube is replaced. A EFB equippped SCA35 was used, with a matched quad of JJ EL84.
Instruments used is hameg 8027 low distortion generator and hameg 8037 distortion analyzer.
http://n.manet.nu/tubedoc/sca35-7199-alternative.pdf
GB-1252 ECF80 and ECF82 used 2 samples, 6bl8 and 6gh8 i had only one of each at the moment of test.
Looking at this small sample ecf80 seems to give lowest overall dist, even slightly better then 7199
( i had a number of 7199, screening them showed no significant differences among individuals)
Note that SCA35 has a DC stabilizing function the most likely reduced the DC differences, in the future
repeating this with a ST70 might show larger differences between tubes. I just have to wait until an unmolested st70 is available for testing.
Two groups of measurement : dist at 1 5 and 15 w output power, and voltages around the phase spiltter where
Va(p) = voltage at penthode plate, Vg2 = voltage at penthode screen and Va(t) voltage at triode plate. These
voltages shows how close the working point is from an ideal cathodyn phase inverter. No components are
changes only the tube is replaced. A EFB equippped SCA35 was used, with a matched quad of JJ EL84.
Instruments used is hameg 8027 low distortion generator and hameg 8037 distortion analyzer.
http://n.manet.nu/tubedoc/sca35-7199-alternative.pdf
GB-1252 ECF80 and ECF82 used 2 samples, 6bl8 and 6gh8 i had only one of each at the moment of test.
Looking at this small sample ecf80 seems to give lowest overall dist, even slightly better then 7199
( i had a number of 7199, screening them showed no significant differences among individuals)
Note that SCA35 has a DC stabilizing function the most likely reduced the DC differences, in the future
repeating this with a ST70 might show larger differences between tubes. I just have to wait until an unmolested st70 is available for testing.
2x’s
Ears for Beers
Hmm, drknstrmyknight was last seen in 2019. Be sure to look at the dates of the posts.
Last post in thread was from GordonW in 2012.
You can always PM people and see if they will reply.
By the way, this is all just FYI.
I get replies whenever I resurrect, honestly it usually comes with an answer that’s been elusive. I do lots of searching first.
Better mids, bass and highs with better separation of instruments and improved sound stage. Not massive gains but an overall improvement. Just put the ST-70 back in rotation a week ago and fired it up with the Kef Q950's. The sound stage truly is amazing. Keb Mo's Suitcase was a delight. These amps are the best bang for the buck with truly great sound. The 7199's were at the low end of their life. I've run weak but still testing good pre tubes with good results before but the 7199's not the case and I wasn't going to pay the high price for replacements of a tube with not the greatest of reputations
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