[R-390] r-390A capacitor question?

[chacuff at cableone.net]

Not sure how this gets blown up...


I don’t remember anyone ever suggesting a wholesale capacitor replacement process in the R-390 series.  I would never suggest changing any of the silver micas unless one has proven itself to be bad.


What has been suggested and debated over the years is wholesale replacement of all paper capacitors in the radio’s.  Many are comfortable with only replacing the filter killer cap in the “A” and maybe the corroding tantalum and letting the others ride.  That’s OK too.  How can one argue with that logic since the person that is going to have to go back into the set when and if any of the others fail is the owner...so whatever one is comfortable with.  


My personal choice is to get all the paper caps out and bring that part of the radio up to date with modern components.  I have done several with the Orange Drops over the years but my next one will be ceramics for bypass and film/foils for coupling.


As big an issue with these radio’s is out of spec. resistors.  We don’t talk about that much but probably has more to do with tube life and performance than the caps.


Of late my choice for my personal listening is to rebuild an R-390/URR and skip replacing anything but a few resistors as needed...an added cooling fan and cleaning, lube and alignment.  Better sounding radio too...


Cecil

K5DL



From: Tisha Hayes
Sent: ‎Friday‎, ‎May‎ ‎30‎, ‎2014 ‎6‎:‎16‎ ‎PM
To: R390A

One time I was bored and did a components/ value count on the R-390A and
was amazed at just how many mica caps there are in the radio. Most of what
is in place in the RF and IF decks are pretty high quality components and
just shopping out the materials list it came to almost $150 in capacitors
if someone was so inclined to shotgun the radio.

Other than the issues with breaking turrets, burning wires, cold solder
joints, etc... If you had decided to go that route of a wholesale
replacement of every capacitor (where 99% of them are good) you would need
to go through an extensive realignment of the receiver as the ever so
slight (but still within tolerance) changes of capacitors is going to cause
a cumulative misalignment on every band and with every function.

Saves your money, eutectic solder, teflon tubing, sore eyes and heartache
and troubleshoot down a problem to a specific component and just replace
that one part. Easter-Egging is a holiday, not a valid troubleshooting
technique.

There have been a few lists of capacitor tweaks in the audio chain that
slightly improve frequency response and THD. They are in the archives and
are a less drastic change than the Kleremonos (spelling) audio mod. If I
was to go that route I would just take the diode load output and run it
into a good audio amplifier or even a software based DSP.

-- 
Ms. Tisha Hayes. AA4HA

*""In this denial of the right to participate in government, not merely the
degradation of woman and the perpetuation of a great injustice happens, but
the maiming and repudiation of one-half of the moral and intellectual power
of the government of the world." -- Fredrick Douglass"*
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