[Central-Electronics] 100V question

[Jim Candela]

Don,
   I am a 20a guy here, but I just looked at the 100v schematic.
I am thinking that a 1v drop of the 150v line (Pk) isn't too bad. Perhaps the VFO is shifting? If so, the 150v line (Pk) is down regulated to an NE-2 neon bulb (about 65v +/-) feeding V17. Perhaps that NE2 could be replaced with a like voltage zener diode?

The LV B+ dropping from 340 to 310 when key down might be normal. Might substitute in another 5U4 for V23. The LV B+ dropping resistor, R4-20 (3K 20W) to the VR tube V26, OA2, might also have drifted high. 

Could be many things, but my bet is the NE-2.
With a 20a, the BC-458 often moves after key down because the filament voltage drops a little. I recall an experiment with a pile of 1626 oscillator tubes. I would try one, and with a variac, I'd vary the AC line voltage from 110 to 120vac. Some tubes moved a lot in frequency (several Khz), others moved a little (maybe 300hz), and some did not budge. I chose the one that did not budge. One secret with tube VFO's is to regulate the filament voltage, or select tubes from a pile for minimum shift from a varying filament voltage.
Good Luck,JimWd5JKO


      From: Donald Ball <gesticart at gmail.com>
 To: central-electronics at mailman.qth.net 
 Sent: Friday, December 29, 2017 1:31 PM
 Subject: [Central-Electronics] 100V question
   
I am having problems with the regulated 150v line. It will shift down 1volt
when I transmit. This causes my audio to shift in pitch. As is I cannot use
the rig like this. It seems the 350v line will drop to around 310 volts
when I key up. I think this is starving the current required to keep the
150 stable. I think this is related to the CW chirp that is mentioned in
the manual. When i remove the 6BQ5 tube this voltage shift goes away. I am
assuming the bias on that tube is off.. ?? I measure the correct voltages
around the tube, but the tube might be too hot and requires less bias??
try different 6BQ5 tubes??  I have tried an external 150v source and its
stable. I could modify the rig to use a series pass IGBT and use the OA2 as
the reference, but think this is covering up a problem that can be
resolved. I think this 100v drifts worst that my Swan 500. Do these rigs
drift that bad? My 20a and 458 VFO are rock solid. I also have a 200V I am
restoring and it is really different from the 100v, it makes me think the
100v had issues and the 200v was the solution. Can someone shed some light
on this?
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