bias trouble ?

[rectifier]

i have one socket that wont bias below 27ma ...i like to run mine cold like rectifiers to get a more spongy feel... i have a new set of ruby tubes 6l6 in there and tried others with no avail... is the pot broke?

 

[bj4rd]

i had an issue with my amp where the 1 ohm resistor in the bias circuit went out of tolerance and the test point was giving me false readings. maybe one of the components on your board is bad???

 

[rectifier]

i may have to have it serviced,,i dont want itto takea crap on me live.

 

[JKD]

I wonder if the tube is out of spec. tho? Did you check and make sure if it follows the tube or stays with the socket? It sounds like you did..just confirming

I had this exact symptom with my RM50...I couldn't match any previously matched sets...and my board was toast when I looked inside.

Difficult to get an exact measurement on components in circuit but these are easy to get to and check if you are comfortable with dropping the chassis out...it's right between the tube fuses if you look for the pics of my dead board or new board....

...please read on for the warning about lethal voltage (sorry, I shouldn't have just assumed you knew!)

 

[bj4rd]

i would recommend getting it serviced or checking it out yourself if you have the know how. there is definitely something wrong if you can't get the bias reading below 27mA. caution: don't get into the chassis yourself unless you know what you are doing because there could be lethal amounts of voltage in there even when the amp is unplugged.

 

[rectifier]

i just popped in a new set of jj EL34L tubes and the problem is not there...just with 6l6 tubes....man thats weird... i didnt see anything wrong with the board...jkd did you fix yours yourself?...i dont see a list of service centers on randalls site unless i overlooked it..... will a different fuse rating cause that?...

 

[JKD]

Did your 6L6 always do this are did it just start? Hard to eliminate the tubes or the bias circuit tho'...

EL34 tubes require you to turn the pot up a lot higher though..so it could be either a problem tube or a problem in the low range of the pot.

I have the opposite problem with a pair of EL34 in my new board...I turn 'em up but it goes from about 30mA to 50mA in a gnats whisker of a turn....

 

[rectifier]

i just got this head used off the board...so dont know much about the history of it.. only thing i did was replace a blown fuse with a 250v 3amp fuse (only one i had }....