[audiomaniac]

Hi all,

First and foremost, I hope everyone is staying safe and well in these crazy times.

I have a quad of Gold Lion KT-77s and I thought I would try them in my Ultavalve. They are not that old and probably have less than 100 hrs on them. Anyway, they sound pretty good. But after I set the bias and ran them in a little, the most I can get out of them is around 1.35v. They replaced some EH 6CA7s that I was easily able to set around 1.5v. My other tubes are Sylvania 6GH8As and a Sovtek 5AR4. I do not know the age of the tubes other than the KT-77s.

My question is if this is normal for KT-77s to bias so much lower and also do they put out less power than 6GH8A/EL34 tubes? Is it possible that the Sovtek 5AR4 is getting weak and not allowing me to be able to set the bias higher on the KT-77s? I never like running anything flat out but that's what I'm pretty much doing with the KT-77s.

Thanks

[Lefty052347]

After going through 2 sets of 6ca7's, I tried a set of KT-77's.  I had no problems with them but went back to 6ca7's due to cost.  I didn't think the KT-77's were worth the extra money. 

I ran the bias between 1.4 and 1.5 volts.

I have had my Ultravalve for over 10 years.

Regards,
Dean

[audiomaniac]

After going through 2 sets of 6ca7's, I tried a set of KT-77's.  I had no problems with them but went back to 6ca7's due to cost.  I didn't think the KT-77's were worth the extra money. 

I ran the bias between 1.4 and 1.5 volts.

I have had my Ultravalve for over 10 years.

Regards,
Dean

Hey Dean, thanks for the info. Yeah so I guess something is off with my amp if I'm only pushing 1.35v wide open. I might check with Frank but I'm thinking the rectifier tube might need to be replaced.   

John

[avahifi]

Your issue is either a low output 5AR4 rectifier tube or a set of out of spec low gain KT77 output tubes.  Replace the 5AR4 first.

Frank

[audiomaniac]

Thanks Frank! 

John

[avahifi]

Make sure you get a real 5AR4 tube.  There are rebranded fakes out there, usually with smaller glass envelops.

[audiomaniac]

Will do.

Thanks

[audiomaniac]

Well, it turned out to be the KT77s. I got a nice new 5AR4 though. Back to the 6ca7s. So much for my big tube adventure!

[pehare]

How do you like the amp?  I've always wondered how the Ultravalve sounds I've never even heard a ST70

[audiomaniac]

I absolutely love this amp! It's very robust and sweet sounding. If I could run it mono I'd buy another one.