[Johnson] Pacemaker

[Richard Knoppow]

    If I read this right you mean unlikely. Actually, its a pretty good 
suspect considering the age of the rig. Even though silver mica caps 
usually are among the most stable types some, mainly the postage stamp 
kind, become quite unstable and change value due to oxidation and 
migration of the silver plating. This is probably due to the ingress of 
moisture. The caps change value and can also jump around and become heat 
sensitive. The symptoms can be popping or warbling of oscillators or 
just a change in tuning.  The only cure is to replace the cap. In may 
cases a modern polypropylene cap is as stable as the original mica and 
may be easier to find. The caps in phase shift networks are often of odd 
values. In any case at least check it and perhaps replace it. For some 
reason caps made during the mid 1950s to mid 1960s seem to be the worst 
offenders. A google search for silver mica disease produced a lot of 
hits but no good tutorials. In any case its worth attention.

On 9/23/2017 9:10 PM, Robert Nickels wrote:
> I'm again trying to convince myself I need to tear into the RF phasing 
> network on my Pacemaker.   It has good suppression on some bands but 40 
.   And since the
> inductor is unlikely to have changed value, that leave the capacitor, 
> which I can see is a silver mica type, which makes it an unlike culprit 
> as well.   
-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL