In my limited experience of repairing the likes of FT101s I have found
evidence that the equalising resistors across the HV diodes fail and take
the rectifiers out with them. These resistors perform two tasks, one as
"equalisers" and secondly as "bleeders", sadly the failure of the rectifiers
can end up destroying the mains transformer if not correctly fused. In the
UK Maplin Electronics stock 1000v rated resistors, I tend to use 1M in place
of the original 470k and it seems a tidy solution. In the case of the FT101
it is tidier than to remove the equalisers and put bleeders on the reservoir
capacitors.
Speaking from bitter experience the FT101 is fine without bleeders or
equalising resistors, however even when powered off for days the HT is still
high enough to bite you, jumping backwards in the shack may be my primary
type of exercise but it is not recommended!
Recently I used some of my "N.O.S" resistors for a project, I was somewhat
alarmed to find they had gone up in value by approx 20%, may be worth
checking if you are changing individual resistors across the reservoirs.....
Regards David G0FVT
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