Carl mentioned about using .01 uf caps from each hot leg of the 120/240 line
to chassis..and tingling.
That scheme was used on my real old drakes..except that they only had a 2 x
prong
120 vac plug ! [ caps wired hot to chassis..and neutral to chassis]. One day
I had nothing connected to the
r4c/t4xc.... and got tingling, when touching the r4c chassis..and external
grnd [ another piece
of gear that was well grnded. ]
If u re-draw it, there is 2 x .01uf @ 1kv disc ceramic caps in series, with
their CT bonded to chassis.
The 120 vac is dropped across both of em. IE: 60 vac across each cap.
That explains why I measured
60 vac between drake chassis....and external grnd. In normal operation,
all the radio gear chassis's are
bonded via interconnecting coax braids, and also the myriad of phono to phono
rca connectors on the small
coax used for the various functions between the Tx and RX box's.
Apparently, per W8JI, IF .01uf caps are wired between 120 v hot leg and
chassis, and also neutral to chassis,
[or between each hot and chassis on a 240 vac input device]... the caps must
be UL rated caps for just that
purpose. The common garden variety .01uf @ 1 kv disc ceramics do not cut
it any longer. The UL rated caps
for this transient / RF bypass protection are 2500 V rated devices.
Apparently too many fires started with non
UL rated caps..as many would fail shorted. A similar thing happened with
garden variety 130 v rated MOV's....
too many house fires. Modern MOV's for 120/240 v use, will have a 3rd lead
sticking out [offset to one side]
and an internal fuse built into em.
I see no reason why .01uf @ 2500 v rated /UL rated bypass caps can't be used
from each hot leg of the 240 line
to chassis, fused or otherwise, in a typ B+ HV supply. Then also well grnd
the chassis of the same B+ supply.
[either from a standard 4 x conductor ...'2 x hots, 1 x neutral, and 1 x
grnd]...or a separate wire from chassis of
B+ supply to station grnd [SPG], RF deck, etc.
Now this should kill any transient, before it even gets into the primary of
the plate xfmr, alleviating the need
[or perhaps in addition to] for a HV bypass cap across each leg of a FWB.
Carl had mentioned about using
a .0047 uf @ 6/10/15 kv disc ceramic across each leg, 4 in total.
In the last Orr book, they used a RC snubber [ which I think was a 100 ohm, 25
watt ww in series with a .01uf/
.005uf @ 3/6/10/15 kv rated disc ceramic]... and snubber was wired directly
across the sec of the plate xfmr.
I see no reaon why a .01/.0047 uf @ 3/6/10/15 kv cap couldn't be wired directly
across the plate xfmr SEC.
Correct size movs on the 240 v side should also work.
Later.... Jim VE7RF
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