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In Reply to: RE: I was speaking about posted by artemus on August 12, 2021 at 04:22:27
I looked at the tube4hifi website and there is no indication that the new output transformers for the VTA ST70 are a different primary impedance than the old ones.
"The A-470 output transformers are brand new USA made custom production transformers. They use the same interleaved/layer winding
technique as the original cloth lead A-470's and incorporate the same high quality M-6 grain oriented laminations.
They are dimensionally accurate to the original design and have a durable heat resistant black epoxy finish."
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
Recomended the KT-66. That was 12 or so yrs ago. I can only tell you of my experience with the VTA ST-70 and Bob's recommendations. Others May prefer the El34. It becomes a matter of tastes.
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You paid HOW MUCH for that electrical receptacle?!!! Are YOU nuts?
It's not a matter of taste in terms of maximizing the tube's performance. Like the 6L6 family, the KT66 performs optimally with an a-a load around 6.6K or 7K. It really makes no sense to use anything other than the EL34 in the ST-70.
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Buy Chinese. Bury freedom.
I did that in the 80's and it was the worst purchaser I have ever made. Lesson learned. Good #'s do not necessarily add upo to good sound.
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You paid HOW MUCH for that electrical receptacle?!!! Are YOU nuts?
"Good #'s do not necessarily add upo to good sound."
That's true, but changing the operating conditions so a particular tube produces worse performance is not a recipe for success.
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Buy Chinese. Bury freedom.
at 4300 ohms the power is down and the distortions are up. But some people like distortion so a person can say "it's a matter of taste". I wouldn't be one of those people. :-)
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I've been wrangling with this problem myself due to the older HK amps I'm rebuilding. The transformers are 3.6K to 3.8K, non-UL, and they weren't meant for the EL34. The original tube was a beam power type, no longer available, and the EL34 is now the only tube that matches. Unfortunately, because it's a true pentode, the screen requirements of the EL34 in pentode mode are very challenging. You can't just use a dropping resistor and a bypass cap as is usually done with 6L6 types. I have at least four amps like this to "re-create", and it's giving me headaches and serious heartburn. :(
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Buy Chinese. Bury freedom.
So are you saying that they are best used with a EL34 output tube?
Honestly, I'm thinking of replacing the driver board and going back to the stock version with a 7643 driver tube.
4300 ohms matches up with a el34. The KT66 needs a higher impedance."Honestly, I'm thinking of replacing the driver board and going back to the stock version with a 7643 driver tube."
OK, now you've got me confused. The original ST 70 used a 7199.
I assume the "original" aftermarket driver board used a 7643?
edit. I see. the 7643 is a sub for a 7199.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 08/12/21
Where did you see that info. Tre'? My understanding is that there is no direct substitute for the 7199.
Inmate Cleantimestream reports that the 7643 is a sub for the 6GH8A, as does Airtime, using it in his Sherwood S5000, which he converted from the original 7199.
I'm only pointing that out so that someone doesn't invest in the 7643, thinking it's a direct substitute for the 7199, unless you found info to the contrary.
You are correct. There are no direct subs for the 7199. I just didn't know about the 7643 being used (with a rewire) in place of a 7199. That's new information to me.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"perhaps the best 9 pin pentode/triode ever... {Opinion}." (link to post below)
ask Jim McShane what tube would he use if it was his stereo. That's the extent of my vast tube knowledge - ask Jim.
I'm throwing myself a party.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
and the new a470 output transformer is 4300 ohms primary just like the old one.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I'm looking at the VTA line.... How would I find the impedance of the transformer for the ST120 or the MONO M125?
Each of these amps has multiple tube choices LISTED but like the ST70, one or another may actually be a better match....
Bob Latino has RETIRED and is either messing about in his shop or out fishing......???
Too much is never enough
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