<thanks for posted and non-posted responses everyone>
summarizing:
People have suggested the grid resistors may have suffered
from long-term excessive grid current. Also possibly from
the dc current thru the shorted caps, but that should have been low
enough to not be a cause of the change in carbon resistor value, I think?
carl:
> those grid caps are supposed to be 200 PF each.
In looking at it closer, I suspect a botched repair job was done. The
grid resistors have red insulation over the leads that doesn't match the red
insulation used elsewhere in that area. And some red insulation has apparent
iron
burns. So I think someone put the wrong caps in during a repair.
(not sure if they're dipped mica..small,round)
Joe mentions that maybe someone was trying to get better RF grounding of
the grids.
carl made a comment about the tubes, but I think he just misread/overlooked
some of my <long>:) notes.
The resistive short thru these caps seems to have been the culprit with the
relay.
With the tubes out the relay was still sticking.
Relay now works fine when I removed the caps.
Caps were damaged as well as wrong!
I was thinking the tubes are probably ok. I was getting full power on all bands
except 10 which had the blown contact. The odd thing at the time,
was that it worked (amplified) while on standby, and the T/R relay stuck.
carl:
> The grid resistors may have changed from grid current overload due to a
> parasitic
> oscillation.
Interestingly, I notice the FL-2100Z schematic specifies 3W resistors
instead of 1W resistors here. Odd since I would think the currents would be
similar in the two designs? (mine is the FL-2100B. earlier model)
FL2100Z schematic is at http://hamradio.online.ru/ftp/fl2100z.zip
Wonder if Yaesu was just responding to in-field failures of unknown cause with
the FL2100Z 3W resistors.
I had gotten some 1W metal oxide replacements already.
Maybe I should order up some 2-3W (larger size recommended by Gudguyham).
Carl points out there should be relatively little current thru them though.
carl:
> There are also two other caps you need to look at, C208 and
> C209, .01 and 2mfd , respectively .! The grid to gnd caps. should be at
> least 500 v to be safe, ..... mica is best <snip>
Thanks, Carl. I'll check these out.
Also: thanks Rich M. for an email exchange on the band contact switch.
I have some old wafer switches I can steal contacts from. suggestion was:
drill out rivets on old contact and remove,
use #0-80 brass nut screw, and silver solder to attach new contact.
other suggestions while working on it:
-Rich's parasitic suppressor kits
-Bias change for Svetlana
-soft key (I do have a external optoisolator circuit I use already)
thanks,
-kevin
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