[Elecraft] K3 power supply recommendations

[Jim Wiley]

Bill -

Older Astron power supplies can continue to give good service, there is 
no reason to replace it unlessit seems to have a problem.

One of the things that does go bad in these supplies, particularly ones 
of this vintage, is that the main filter capacitor "loses its 
microfarads"(dries out).  The capacitor has to handle a fairly large 
ripple current, especially if the power supply is working hard, and that 
in turn can have detrimental effects onthe big capacitor.   I recently 
encountered a RS-35A with exactly that symptom, the power would dip 
momentarily at voice peaks when running a 100-watt transceiver.  The 
voltage was fine for receiving and anything less than full output, but 
when  a big voice (or CW) peak came along that demanded more than about 
16 amperes from the supply, it lost regulation, which caused all sorts 
of weird and wonderful things to happen to the transceiver -such as loss 
of PLL lock, frequency shifting, mode shifting, and so on. .

The cure was to replace the 30,000 uFd / 30V capacitor in the RS-35A 
with a newunit.  As it turned out, new capacitors of that exact 
specification were a bit hard to find, and expensive, but a search of 
theMouser catalog turned up a great choice. I found a 33,000 uFd / 35 
volt unit for a reasonable price (about $35.00 including priority mail 
postage).  The new cap is both a bit smaller (physically) than the 
original, and has significantly better specifications.  The Mouser part 
number is 647-LNT1V333MSE.  The new capacitor has the same connection 
terminal spacing, so the control board just bolted on.  I did mount the 
board slightly differently, but that is justpersonal preference.  The 
original mounting method will work fine.

Here (I hope) isa direct link to the Mouser catalog page: 
647-LNT1V333MSE 
<https://www.mouser.com/Search/ProductDetail.aspx?R=LNT1V333MSEvirtualkey64700000virtualkey647-LNT1V333MSE>

Result: The oldAstron gets  new lease on life - it works just like brand 
new, and I expect may more yearsof service.

Perhaps the Astron RS-35A that you have is still working OK, but it may 
be getting a bit creaky, so to speak. Replacing the main filter cap 
can't hurt, and will go a long way toward insuring trouble free 
operation for years to come.

YMMV, of course. No connection with any vendors or manufacturers, just 
satisfied with the results at what I considered a fair price.  Any yes, 
I thought about some of the large computer power supply caps that were 
in my junk box, and I might have tried one if it was "close" - but after 
a bit of thought, the new unit was a better choice and might in the long 
run prove to be less expensive.  Asurplus unit could have its own 
problems, possibly causing a more catastrophic failure.


- Jim, KL7CC



On 4/16/2013 7:27 AM, Bill wrote:
> My RS-35A has been on and in use 24/7 (except during storms and 
> vacations) for well over 25 years. I plan on replacing it "just 
> because" this summer - with a new one.
>
> Bill W2BLC