[JMS] 90281 power supply

Wed Nov 3 14:09:42 EDT 2021

I have S/N 306.  The transformer is sealed as are the filter chokes.  

This supply has the rear panel high-low voltage switch and a terminal strip to elevate HV with a cap-input.  I no longer strap the input cap into the circuit.  The HV supply runs close to the caps' maximum voltage rating, especially when supplied from today's 125 VAC mains.  

I'm on my third set of GE Pyranol caps after initially selecting a C-input.  In any event, I would try and maintain 110 VAC and absolutely no more than 115VAC at the supply's input under any voltage selection.  

Advice:  keep all three supplies.  Depending on their condition, you may want the third supply to cannibalize parts in the future.  

Paul, W9AC

-----Original Message-----
From: james_millen_society-bounces at mailman.qth.net <james_millen_society-bounces at mailman.qth.net> On Behalf Of Brian Harris via James_Millen_Society
Sent: Wednesday, November 3, 2021 1:00 PM
To: The James Millen Society Members Email Reflector <james_millen_society at mailman.qth.net>; Don Buska - The Radio Lab Works <don at radiolabworks.com>
Subject: Re: [JMS] 90281 power supply

Don, et al,
Here is a little more information on the 90281.
I have learned that the design with the hermetically sealed transformer started at serial number 200.  Apparently the previous design ran from likely 001 to 199.  Along with the hermetic transformer there were other changes.  Specifically, the addition of a Hi-Lo switch controlled series resistor in the plate transformer primary and the terminal strip on the rear which allows one to choose capacitive input or choke input.  Another minor change is swapping the positions of the filament and plate switches and their respective indicator lamps.   Although I have not yet quantified this, I estimate the new version is about five pounds heavier than the old version which, in a power supply, is usually a good thing.  So now I have a quandary.  Do I keep the new version because it is obviously more versatile and sell one of the older versions or do I keep all three or do I sell all three and homebrew exactly what I need?  Decisions, decisions! 

Brian Harris, WA5UEK cell 214-763-5977 email cosmophone at yahoo.com 

    On Tuesday, November 2, 2021, 08:51:25 PM CDT, Don Buska - The Radio Lab Works <don at radiolabworks.com> wrote:  

  Hi Brian.  My #168 supply still has the removable bells on the HV transformer.  Mine doesn't have the HIGH/LOW switch either.  I wonder if your 139 and 157 supplies are also absent the HIGH/LOW switch?

 Sorry can't help much on the transition when the hermetical sealed transformer came along, if it truly did.  There are a few with higher S/N's on our JMS website so we should soon know if there was a real transition in the 200's and above.  Naturally if we do determine such a transition we'll need to get a back side picture and add it to the JMS website as well.

 73
 Don N9OO

 On 11/2/21 6:52 PM, Brian Harris via James_Millen_Society wrote:

 I have three 90281 power supplies with serial numbers 139, 157 and 237.

The two earlier numbers have power transformers which have removable end bells. The later one has a larger, hermetically sealed transformer.

Assuming the hermetically sealed unit is original, does anybody have a supply later with the hermetically sealed transformer?   Does anybody know when the change was made and why?

I’m asking these questions because I am going to sell one of my supplies and I don’t want to sell the best version, if there is one.   If one is no better than the other, I will sell the hermetic version because doing so would leave me with a spare supply with the correct transformer and, more important, one which could easily be rewound if I should have a failure.

Thanks for your time. 

Brian Harris WA5UEK
Sent from my iPhone
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