[Milsurplus] C-553 replacement

[Jim Whartenby]

Has anyone ever lost a mechanical filter in the R-390A caused by a C553 failure?  I have repaired or replaced a few filters over the years but the other three filters were OK.  In my experience, it usually seems to be either the 2kc or 4kc filters that fail catastrophically.  Perhaps because more disks are needed for the narrower bandwidth?  The failure of the welds between the disk and wire makes the mechanical filter into an expensive baby rattle.  This is the one failure mode that cannot be repaired on the workbench.  Regards,JimLogic: Method used to arrive at the wrong conclusion, with confidence.  Murphy 

    On Wednesday, July 24, 2024 at 02:16:45 PM CDT, B. Smith via Milsurplus <milsurplus at mailman.qth.net> wrote:   

 When working on the R-390A be sure and replace C553 on the IF deck. This 
cap blocks DC to the mechanical filter which may be destroyed if it 
fails or leaks. I would put that task #1 on any inspection and 
especially prior to resale.
k4che

On 7/23/2024 3:19 PM, Ray Fantini via Milsurplus wrote:
>
> I have worked on a boat load of R-390A receivers but only two R-390 
> receivers. Never bought the cost reduction thing because as you say 
> the changes on the cost verses the added reliability and ease of 
> maintenance on the “A” make the early version of the R-390 a bit of a 
> pig in my book. You can do a mechanical alignment on the “A” with ease 
> but forget about it with the non A, recall something about the 
> regulator tubes being they were some weird twenty four volt filament 
> and were only ever used in the 390 so in Addition to all the heat they 
> added they were hard to come by. Recall that I saw one 390 modified 
> with an additional filament transformer so it was able to use regular 
> 6080 regulator tubes.
>
> Weird thing about the R-390A, a Collins version will sell for twice 
> the money of a non-Collins. The last R-390A I sold was only able to 
> get $325 for it and that was one hundred percent working with covers. 
> The issue was it was built by Motorola and not Collins, think I would 
> have easily gotten $500 for a Collins radio although there is no 
> difference.
>
> Think I paid about $200 for that radio but put maybe ten hours work 
> into getting it right so unless I can pick up radios for $50 to $100 
> don’t think I will be doing any more R-390A receivers to resell.
>
> Ray F/KA3EKH
>
>
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