S.I.R. 100W SuperLead Schematic pt. II

[dukeamps]

https://youtu.be/tbB-7iMWrZg?si=4tw8MteO8nlhc7i-

Wow, this '69 mod' of yours sounds incredible! Well done.

Cheers

[dukeamps]

https://youtu.be/SQYod9k1ZvE?si=cagCW_wIHZRc6aLN

[blacklabel]

Hi guys, I have a question about #34: could you tell me how much to calibrate the bias of the 6550?
in the calculation is considered 25w dissipation like the EL34 or 35w?
cold or hot bias?

Thanks

[Unique]

Hi guys, I have a question about #34: could you tell me how much to calibrate the bias of the 6550?
in the calculation is considered 25w dissipation like the EL34 or 35w?
cold or hot bias?

Thanks

Supposedly, the 6550 is 42W, but I always do mine at 35w, which is what the 6550 was with GE until they came out with their 'A' revision. I've read two sides of the story with that, one being that GE supposedly just changed the spec sheet to 42w to compete with the UK's KT88. While the other story claims that GE bolstered it's 6550 at the request of Fender who were looking for a more robust 6550 for their 400w amp they just came out with back then. Both stories have more details, but this is the basics of it. I find biasing at 35w works well. Besides, I struggle to believe that todays Russian and Chinese 6550's are more robust than the GE's of yesteryear, question how they would hold up if biased at 42w.

In an email Frank sent someone here, which was posted at one time, Frank said that #34 liked a cooler bias. I found this to be true, at least for me. I think a cooler bias sounds much better with this mod, brings out more of it's character. And biasing your tubes with the 35w max dissipation not only aids in that, but is safer for your tubes.

As far as where to bias it at goes, all 6550 tubes are different, even those of the same brand. Also posted here at one time by Dave Freidman, after servicing #34, he stated that Slash liked his bias at 40mV. I find this a good starting point. I rarely go past that. With some tubes, 40mV hits the sweet spot, with others, I find it a little lower with the #34 mod. But generally, I find it close to that with all 6550's I've tried.

I hope this helps.

[blacklabel]

Hi guys, I have a question about #34: could you tell me how much to calibrate the bias of the 6550?
in the calculation is considered 25w dissipation like the EL34 or 35w?
cold or hot bias?

Thanks

Supposedly, the 6550 is 42W, but I always do mine at 35w, which is what the 6550 was with GE until they came out with their 'A' revision. I've read two sides of the story with that, one being that GE supposedly just changed the spec sheet to 42w to compete with the UK's KT88. While the other story claims that GE bolstered it's 6550 at the request of Fender who were looking for a more robust 6550 for their 400w amp they just came out with back then. Both stories have more details, but this is the basics of it. I find biasing at 35w works well. Besides, I struggle to believe that todays Russian and Chinese 6550's are more robust than the GE's of yesteryear, question how they would hold up if biased at 42w.

In an email Frank sent someone here, which was posted at one time, Frank said that #34 liked a cooler bias. I found this to be true, at least for me. I think a cooler bias sounds much better with this mod, brings out more of it's character. And biasing your tubes with the 35w max dissipation not only aids in that, but is safer for your tubes.

As far as where to bias it at goes, all 6550 tubes are different, even those of the same brand. Also posted here at one time by Dave Freidman, after servicing #34, he stated that Slash liked his bias at 40mV. I find this a good starting point. I rarely go past that. With some tubes, 40mV hits the sweet spot, with others, I find it a little lower with the #34 mod. But generally, I find it close to that with all 6550's I've tried.

I hope this helps.

Thanks Unique, you are always super helpful.
Do you have any preferences on today's 6550s? I have always used the svetlana 6550C sed but now it is no longer safe to buy them and they cost too much.
I was thinking about the bottle-shaped tung sol reissue or JJ.

[Unique]

Hi guys, I have a question about #34: could you tell me how much to calibrate the bias of the 6550?
in the calculation is considered 25w dissipation like the EL34 or 35w?
cold or hot bias?

Thanks

Supposedly, the 6550 is 42W, but I always do mine at 35w, which is what the 6550 was with GE until they came out with their 'A' revision. I've read two sides of the story with that, one being that GE supposedly just changed the spec sheet to 42w to compete with the UK's KT88. While the other story claims that GE bolstered it's 6550 at the request of Fender who were looking for a more robust 6550 for their 400w amp they just came out with back then. Both stories have more details, but this is the basics of it. I find biasing at 35w works well. Besides, I struggle to believe that todays Russian and Chinese 6550's are more robust than the GE's of yesteryear, question how they would hold up if biased at 42w.

In an email Frank sent someone here, which was posted at one time, Frank said that #34 liked a cooler bias. I found this to be true, at least for me. I think a cooler bias sounds much better with this mod, brings out more of it's character. And biasing your tubes with the 35w max dissipation not only aids in that, but is safer for your tubes.

As far as where to bias it at goes, all 6550 tubes are different, even those of the same brand. Also posted here at one time by Dave Freidman, after servicing #34, he stated that Slash liked his bias at 40mV. I find this a good starting point. I rarely go past that. With some tubes, 40mV hits the sweet spot, with others, I find it a little lower with the #34 mod. But generally, I find it close to that with all 6550's I've tried.

I hope this helps.

Thanks Unique, you are always super helpful.
Do you have any preferences on today's 6550s? I have always used the svetlana 6550C sed but now it is no longer safe to buy them and they cost too much.
I was thinking about the bottle-shaped tung sol reissue or JJ.

You're welcome. As far as today's 6550's go, Tung Sol sound the best to my ears, and I've tried them all except JJ's. The JJ's don't sound too bad in many YouTube videos, but I'm not sure how well that would translate to hearing them in person? Tung Sol would be my choice for new tubes. I think they serve the #34 sound well.