Bee Pre dropped channel [resolved]

[joepiecuch]

after something like a couple of years of daily problem-free use, my Bee Pre has lost audio on the A channel. the issue doesn't follow tubes, which all glow. observing power up from the underside, i note that the LEDs on the A channel c4s light up much more slowly than the ones on the B channel. furthermore, the b-side LEDs on that c4s board start to light up and then drop out while the LEDs on the a-side of the board stay lit. that seemed like it might be a distinctive sequence of events suggesting something specific. if not, what further diagnostic info would be helpful?

 

[Paul Birkeland]

What are the IA, OA, IB, OB, and Kreg voltages on the bad channels?  Pos IN and pos OUT are probably also helpful. 

You're welcome to make the drive over here too, you know where I am!

 

[joepiecuch]

IA        187  186
OA        145  145
IB        145  145
OB          98  142
Kreg      4.7    3.2
Pos IN  13.9  13.9
Pos OUT  9.9  9.9

yep, if it comes to that, i can find you!

 

[Paul Birkeland]

The high OB voltage in conjunction with the low Kreg voltage mean that the 300B on that side isn't drawing any current.  This can happen for a wide variety of reasons like a broken wire, loose component, loose socket, stuff like that.  If the BeePre hadn't ever worked, solder joints (especially on the center leg of each MJE5731A) can totally cause this problem, but that's less likely since the BeePre has been in service for a while. 

 

[joepiecuch]

thanks; so OB should be approx. 100 and Kreg approx. 5? i think i'll do some pin and socket cleaning and tensioning as a first step.

 

[joepiecuch]

well...it would appear that it was, after all, the tube. for laughs i swapped in an old JJ and suddenly everything was testing ok; put back the EH and bad readings returned. apparently when i thought i traded sides with the original pair i did not. or something.