[Central-Electronics] 100V Problem/Questions

[GRANT YOUNGMAN]

I have a very nice 100V that I restored several years ago, complete with a Tusa-rebuilt PTO, that was working fine last time I had it on line.  No good deed going unpunished, I decided to bring it back into the mix paired with an SX-115 as well as rework the mic cable routing to eliminate the little bit of hummmm that won’t go away, and of course, it wasn’t working.

Specifically it worked fine on 15M, but would produce no output on any other band.  In working stage by stage through the RF chain, I’ve settled in on the V14 6BQ5 driver stage.  “Sometimes” — after wiggling the tube and/or the coil plugin it will begin producing output on all bands for a while.  I can wiggle the tube and usually force it to work on a band that produces no output.  But then it eventually goes back to working on 15M only.  Clearly, there’s some kind of mechanical issue, bad solder joint, etc. with the socket or something around the socket, but whatever it is it doesn’t effect 15M operation, ever.  In the process I’ve checked pins on all of the plugins, including the RF deck, cleaned them up, applied some D100L, etc.

Also, when checking the bias on pin 3 of the 6BQ5 it is around 0.27-0.29v (depends on band) rather then the 0.32v spec.  So I’m going blind tracing through the schematic and also visually inspecting the hard-to-see mess around V14 (6BQ5) to attempt to figure out what might be amiss.

Two questions:

1.  Anyone have a clue what is different if anything about 15M that would leave it unaffected by whatever might affect 10,20,40,80 intermittently?  10M input (by the meter) on CW will only run up to around 100W, but when it works at least there’s something.  

2.  Is the bias on pin 3 of the 6BQ5 (spec’d at .32v) critical enough that I should rework the voltage divider to get it up from the (around) 0.28v current value?

Thanks … Grant NQ5T