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how to adjust bias for kt77 tubes in Jolida 302

I just got a set if KT77 tubes to try in my Jolida 302brc amp. The "easy bias" lights do not come on when I adjust the bias pots. The manual says to use multimeter and adjust bias to 400 - 450 millivolts but the pots only go up to about 180 millivolts. I am a little confused here. Some on-line resources say bias at 40 - 45 mv, that's 1/10 what the manual says.
winggo
4 responses Add your response
josefm
53 posts
 
Yeah, you need 'hotter' biasing tubes, I had a GL KT77quad that couldn't make bias too. Sent them back and the replacement quad made bias just fine.
I have an older 302 and the manual says 35-45 mV. for EL34 types, so not sure about the newer 302brc.
winggo OP
25 posts
 
I called Jolida and Mike said that the KT77 should drop right in and work very much like the EL34's. He thought the tubes might not be good. They were supposed to be new tubes. I sent them back and will see what the seller says.
winggo OP
25 posts
 
The original EL34's will bias just fine. I called the company that I bought the KT77's from and they said that the range of the bias pots was not enough to accommodate these KT77's so I may have to send them back. I'll call Jolida and see if there is a way to modify the amp to accept the KT77's.
joeinid's avatar
joeinid
658 posts
 
Can you bias other tubes like EL-34's properly with the EZ bias lights? Is there a switch on the back to change the bias voltage for other tube sets?
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