Some may remember a few weeks ago, I posted a request for info re a
replacement Bandswitch for the Clipperton-L I had just bought. The best
advice I got was from Tom Rauch- who recommended a switch from an AL 82. I
got this switch, and, by keeping the old wafer that switched some Caps, I
got a reasonable 'Fix'. The spacing on the wafer controlling the tank is
much better. It cost a bundle, but the quality was good.
After completing the 'fix', I did a review of the old tank wafer- and found
some surprises. Among them was the fact that the 'burn' had occured in the
10M position, despite the fact that the 10M Mods had only half been done.
"Somebody" had been sloppy and hasty. The person I got it from told me he
had never used it in the 160M or 10M positions, so it must have been the
original owner.
The 'Mods" to allow 10M operation, for this Amp, have two separate
operations; first, there is a filter in the input line that must be
removed. This was NOT done, despite the fact that this is the easier part.
Second, the switch and tank coil are taken out to the point where the
'stop' on the switch can be moved over one step. This was done. THe taps on
the coils for 10M were already in place in the switch position that is
originally blocked.
The location of the 'burn' smudges show that the switch was in the 10M
position when it arced. It appears that the arc then affected the open
wiper for the 160Mposition, that is tied to the 'constant' wiper, and
perhaps arced to ground at the wafer mounting screw, which is between the
10m wiper and the 160M wiper. Lots of melted metal; all the 10M wiper
'fingers' are gone, and half the 160M fingers (on the side nearest the
screw) are gone.
Another surprise was that the switch had been burned before, and some
repairs had been done. The wipers for the 10M and 160M positions had been
replaced (evidence is that the tubular rivets on the wipers had been
replaced with small machine screws). Another wiper set (20M) had been
replaced or 'fixed' by the use of a copper wire rivet instead of the
tubular original. The deposits from the latest burn were liberally coated
on the replacement screws.
A rather stupid thing showed up when I was following the circuit in the
process of making the repairs- The ORIGINAL tank coil and switch diagram
has the tank wafer and switch drawn in backwards! THe only other place I
have seen this is in the MFJ diagram for the 949 tuner. They probably both
had used HighSchool trainees as Draftsmen, without adequate checking.
Question for the group- do you think the filter still inplace contributed
to the arc-over, are is it probable that it was a 'hot switch' error? I
thought this tale might help someone else with a similar problem .
I found it interesting and educational, even if the condition was a
surprise, when I checked the Amp out.
Any comment?
Bill-W4BSG
-
Bill Aycock --- Persimmon Hill
Woodville, Alabama, US 35776
(in the N.E. corner of the State)
W4BSG -- Grid EM64vr
baycock@HiWAAY.net
w4bsg@arrl.net
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