[R-390] To swap or not to swap those aging "reddish" rectangularmica caps

[Jordan Arndt]

>From experience, before you start on the transformer cans, you might be wise 
to replace the 51pF, 68pF and 51pF caps across the 1st IF cans. C318, C329 
and C334.
One other cap you might look at replacing is C227, a 100V .047 canned paper 
capacitor. It sits between the 6DC6 and the 6C4. You can cut the lead at the 
base of the cap, and then fish it through to where you can mount a film cap 
to replace it.

I once managed to connect a C227 replacement cap to the tube base pin 
successfully, but I wouldn't go through that process ever again.

It's not necessary to replace all the caps in the topside cans, but what you 
can and should do is inspect them internally, make sure the variable caps 
are not frozen (they can be repaired), clean the pins and spray some contact 
cleaner on the pivot point of the variable while turning it.

The real test of the components inside the RF cans will be in alignment and 
testing, where you might see poor tracking, cores that won't tune or tune 
only at the extremes of insertion depth, etc...

I hope this info helps...Good luck..!

73...Jordan VE6ZT


----- Original Message ----- 
From: "jkharvie via R-390" <r-390 at mailman.qth.net>
To: "R-390 Mailing List" <r-390 at mailman.qth.net>
Sent: Thursday, July 04, 2024 1:13 PM
Subject: [R-390] To swap or not to swap those aging "reddish" 
rectangularmica caps


> Guided discovery continues as I make progress on the RF sub chassis.I 
> received C327 replacement for "high Q" 100pf, 1,000 volt mica capacitor to 
> install on the primary output of T207.I received group input that the 
> green mica mold caps provides acceptable operational service with very low 
> failure rates, and the "reddish" color caps are older generation and 
> appear to have a statistically higher failure rate, and should be replaced 
> with new high q mica caps.Two examples in the receiver, (1) with all 
> reddish mica capacitors, and (2) 1 out of 2 reddish capacitors.My course 
> of action is to keep the green, replace the reddish capacitors.
> Or does the group make the case that while the patient out and ready for 
> surgery to replace both capacitors while opportunity is good?
> Thanks in advance to your vast repository of deep informed knowledge as I 
> work my first end to end refurbishment on this magnificent receiver.Happy 
> 4th of July, celebrate independence day.
> John N3JKE
>
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> Sent from AOL on Android


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