The right rear socket is reading a very high bias. It had been fine and I was checking bias every day. This morning it read 8.something. I shut it off and turned the bias pots all the way down. Swapped the front and rear tubes. Veriac is reading 117v. With all the pots turned all the way down the rear is still reading 8.something. Where should I start looking?
5 posters
High Bias on one socket - fixed !
Mr C- Posts : 99
Join date : 2019-07-11
Age : 69
Location : Visalia CA.
Mr C- Posts : 99
Join date : 2019-07-11
Age : 69
Location : Visalia CA.
Okay.. Heres what I have. Unplugged of course, tubes removed. I get 174K across the 10k bias resistor on the right rear socket. The other 3 measure at..... 10k...
peterh- Posts : 1869
Join date : 2012-12-25
Location : gothenburg, sweden
I hope that the "other 3" measures 10ohm !Mr C wrote:Okay.. Heres what I have. Unplugged of course, tubes removed. I get 174K across the 10k bias resistor on the right rear socket. The other 3 measure at..... 10k...
You have a blown 10ohm resistor, probably caused by a flash-over in the tube .
Change resistor and junk the tube.
Mr C- Posts : 99
Join date : 2019-07-11
Age : 69
Location : Visalia CA.
Oops.. I typed the values in wrong. Yes, the other 3 measure 10 ohms. The right rear measures 174K ohms. I talked to Bob and I have a replacement on the way. I have maybe 60 hours on the unit. I had just put a set of KT120s in about 10 hours ago.
peterh- Posts : 1869
Join date : 2012-12-25
Location : gothenburg, sweden
Thats good, you should be able to find a matching tube from the dealer.Mr C wrote:Oops.. I typed the values in wrong. Yes, the other 3 measure 10 ohms. The right rear measures 174K ohms. I talked to Bob and I have a replacement on the way. I have maybe 60 hours on the unit. I had just put a set of KT120s in about 10 hours ago.
A tube that has flashed has a large probability to flash again, that's why it should be
replaced with a fresh one.
HarryY- Posts : 46
Join date : 2019-07-24
Location : NY
When you install the resistor make sure the leads can flex a little for thermal expansion and contraction
Steve G- Posts : 18
Join date : 2017-03-17
Location : Carson City, NV
I would quit checking bias everyday. I check mine occasionally and it stays within a couple tenths, don't want to be chasing it. I also use KT120's
LeGrace- Posts : 389
Join date : 2016-08-07
Location : Ontario, Canada
You continue to follow in my footsteps. I will reiterate prior advice, look into adding autobias module.
Mr C- Posts : 99
Join date : 2019-07-11
Age : 69
Location : Visalia CA.
Yesterday the 2W 10 ohm resistor arrived and I got it in place. It's holding it's bias and sounding fantastic once again.