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In Reply to: RE: Biasing KT-77s in a Conrad-Johnson MV-60 posted by RhythmDevil on March 04, 2016 at 08:01:27
Use the tubes the amp is made for ( EL34)
Why change a winning concept ? It can only be worse!
Follow Ups:
He can use the KT-77 Genalex just fine, I help c-j owners fit KT-77 Genalex to their amps all the time. And they are FAR from worse, they are amazing tubes!!
He just needs to get them from a vendor who understands that some KT-77s bias too cool to drop in an EL-34 socket. That's why his light won't appear - there isn't enough bias range to accommodate a VERY cool (low current) biasing KT-77. He simply needs hotter biasing KT-77s.
"it can only be worse"
Not really. The Gold Lion KT-77s I am using sound better than any of the EL34s I have tried.
But thank you for your response.
Cerebrate!
"The Gold Lion KT-77s I am using sound better than any of the EL34s I have tried."
Even though the LED indicates that the tube is not biased properly?? WOW! Those tubes must really be magic.
The LED is driven from a comparator circuit that indicates correct current draw.
I suspect those tubes are running hotter than the design calls for, and these is not enough negative grid bias to set the tube current at the intended operating point. You might want to keep an eye on things and look for overheating.
"I suspect those tubes are running hotter than the design calls for"
Actually exactly the opposite is true.
Look, mockery is not required. I told you what I heard. You are welcome to come by anytime to compare in my system and hear for yourself.
I asked what I think is a straight forward question. I will admit that I only know enough about circuit design to be dangerous. That is why I asked the question.
For example, I know that EL34, 6CA7, and KT-77 tubes are generally considered "interchangeable", but YMMV depending on the amp design. You actually got close to answering my question once you gave up being snide, and for that, I thank you.
Cerebrate!
Wasn't trying to be snide, but I do know that although they are pin-for-pin compatible, 6CA7 and EL34 take different grid bias to achieve the same current draw.
I don't know about KT77's.
If your KT77's are working for you and not self-destructing, enjoy them.
Jim suggested they might be running colder than normal. That won't hurt anything,although it might decrease the maximum available power.
Yes, I agree. Sorry, but I can't help the OP with the bias.
I am serious I didn't catch the Mockery part of this.
I do defer to Jim McShane Re: whether the lack of setting off a Bias LED with these KT-77s leads to hotter or Cooler running due to insufficient range of potential bias current.
In my VTL amp I went thru many EL34's, and 6CA7's. The GL77 was by far the best. My amp had adjustable bias and they did bias at a different point than the other types. It might be my all time favorite power tube
Alan
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