wrote in message
...
On May 22, 11:07 am, (Scott Dorsey) wrote:
wrote:
I=92m just about finished refurbishing a Heathkit SB-401 amateur
transmitter that has, according to the manual=92s parts list, five 0.2uF
=93resin=94 capacitors. What are these things and how reliable are they?
Does conventional wisdom dictate that such caps should be replaced?

They are called "resin-dipped" because of the outer casing. You don't
really
care about the outer casing, you care about what is inside. If the
dielectric
is plastic, keep it. If it's paper, replace it.

I=92ve searched the web for information on this, but only get hits
concerning Black Beauty caps, which most always need to be replaced.

Where are the caps and what will happen if they fail? In a receiver IF,
a bad cap can take out an IF transformer, but if it's just driving another
tube stage, the consequences of failure are minimal.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Three are used in the detector for the automatic level control (ALC)
circuit. Failure here probably wouldn’t be catastrophic. Another
provides bypass in the output driver grid circuit, but is shunted by
some large resistors. I doubt failure would do much here either. The
last one provides bypass on the filament voltage to the linear master
oscillator (LMO). In this case, failure as a short could stress the
power transformer.

-Dave, K3WQ

The leakage may only show when the cap is subjected to full
rated voltage. Chances are they will work in filament and
cathode bypass applications without much issue. They rarely
go into a zero ohm failure mode.

If it is part of the time constant for the ALC circuit, leakage
could cause big problems. What grid is it bypassing in the
driver stage--screen or control?

If they are mylar or polyester dielectric they are probably okay.
New caps are pretty cheap, however.

Pete