[JMS] Millen 90281 HV Supply

Tue May 24 09:13:28 EDT 2016

Thanks, Brian.  When the new caps arrive, I plan on measuring input cap
voltage with a scope.  A resistive divider formed with 1% resistors can be
set up in a string to stay within reasonable scope input limits.  

With no load on the supply, the Pyranol caps should remain charged to the
peak voltage from the full-wave 816 rectifier.  That's what needs measuring
with changes in Variac input voltage.  The input caps are housed in a small
compartment under the supply.  There's not a lot of room to experiment with
different caps.  Using oil caps with a higher voltage rating results in
big-size caps that exceed the compartment space.    1.5KV caps may just
barely fit in that area.   Would hate to modify the supply in any
significant way to make the input section more reliable.   

Paul, W9AC

-----Original Message-----
From: James_Millen_Society
[mailto:james_millen_society-bounces at mailman.qth.net] On Behalf Of Brian
Harris via James_Millen_Society
Sent: Tuesday, May 24, 2016 8:29 AM
To: The James Millen Society Members Email Reflector
<james_millen_society at mailman.qth.net>
Cc: Brian Harris <cosmophone at yahoo.com>
Subject: Re: [JMS] Millen 90281 HV Supply

Paul,

It has always been my understanding that all capacitors are rated at wvdc
unless otherwise specified. I will be sure to keep the line voltage at 115
or less when I get around to firing up my 90281.  From your tip, I will also
check the caps on mine before applying power.  

Brian

Sent from my iPhone

> On May 24, 2016, at 6:59 AM, Paul Christensen <w9ac at arrl.net> wrote:
> 
> A follow up to my progress reported below.  I've now gone through two 
> sets of old GE Pyranol oil caps that are on the input to a dual Pi 
> filter.  I don't know if the caps are just old and failing.  Or more 
> likely, the caps are on the ragged edge since Millen specified 1KV 
> caps at the filter input of a dual C-L-C Pi network.  In each case, 
> the caps fail shorted.  The RMS voltage is just over 1KV with a high 
> input peak voltage.  What I'm thinking is that my line voltage runs 
> 127V and normal line voltage in the early 1950s was probably closer to 
> 115V.  So, I've ordered a new set of German oil caps and will only operate
it with a Variac to pull down the line voltage.
> Someone help me remember -- are oil caps rated for WVDC or peak voltage?
> 
> The 90281 has a jumper to bypass the problematic input caps, leaving a 
> choke input.  Sure, I can leave it this way, but it would be nice to 
> have a reliable supply that works as designed.  Anyone have thoughts 
> as to the repeated Pyranol cap failures?  The oil caps further 
> downstream are fine so far and are probably helped with a lower peak
voltage.
> 
> Paul, W9AC
> 
> -----Original Message-----
> From: Paul Christensen [mailto:w9ac at arrl.net]
> Sent: Wednesday, May 11, 2016 7:12 PM
> To: 'james_millen_society at mailman.qth.net'
> <james_millen_society at mailman.qth.net>
> Subject: Wanted: Millen 90881 Band Coils
> 
> Looking for 160m through 20m coil sets for the 90881 500W Millen amp.  
> I know they're scarce but please keep me in mind if you have, or find 
> extra coil sets.  I already have the 10m set.
> 
> Two weeks ago, I refinished the front panels on Millen 90281 HV and 
> Lambda Model 28 power supplies.  I followed the instructions on the 
> VHT wrinkle paint can and would you believe it turned out like a 
> factory job?  When the XYL was out, I used the kitchen oven and set it 
> to 160 degs.  Applied heat for 15 minutes and the job was done.
> 
> I did depart from the instructions with the application of a light 
> gray primer after extensive sanding.  Application of the primer was 
> worrisome but with three heavy coats of VHT, the paint still builds 
> into a consistent black wrinkle finish.  I had previously encountered
paint flaking on some
> old gear that wasn't primed.   So, pretty happy it turned out okay.
> 
> I'll post links to photos on my QRZ.com page when it's all racked up.
> 
> Paul, W9AC
> 
> ______________________________________________________________
> James_Millen_Society mailing list
> Home: http://mailman.qth.net/mailman/listinfo/james_millen_society
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:James_Millen_Society at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net Please help support this email 
> list: http://www.qsl.net/donate.html
______________________________________________________________
James_Millen_Society mailing list
Home: http://mailman.qth.net/mailman/listinfo/james_millen_society
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:James_Millen_Society at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html