FW: [Hallicrafters] Recapping Hallicrafters

[Langston, Mike]

Just replaced the electrolytics in the HV section of my Apache.
Originals were (2 ea) 125 mfd @ 450V in series yielding 62.5 mfd @ 900V
(choke filter). I could only find 125 mfd @ 400V but figured that would
be OK since they are new "modern" caps. The higher line voltage gives me
800V on the plate (supposed to be 750V) under load and the caps
definitely don't like that. Didn't explode, but one got so hot it melted
the plastic coating and started smelling bad enough that I got the HV
off it in time (yes, it has equalizing resistors in the circuit). I
recommend higher voltage ratings in these types of circuits with the
higher line voltages we see today.

The voice of experience (Mike)
KL7CD

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Roy Morgan
Sent: Monday, July 18, 2005 3:05 PM
To: Clayton L. Nicolsen; Hallicrafters at mailman.qth.net
Subject: Re: [Hallicrafters] Recapping Hallicrafters


>One mistake some make is replacing electrolytic caps with one of a
higher
>voltage, this will accelerate the aging of the cap.
>
>I have never heard anyone say this before.

Clay,

I may have said that using an electrolytic at a voltage lower than its 
rating may get you slightly higher capacitance, because the electrolytic

film that forms the actual capacitor is thinner and thus has higher 
capacitance.

Recently, however, I carefully reformed some new old stock can
capacitors 
and noticed that the capacitance was slightly higher at higher reforming

voltages. And the dissipation factor went down as i reformed them.

I think we should use electrolytics aof whatever voltage we have, as
long 
as they are not run above their rating, during use or during startup.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-948-6213
roy.morgan at nist.gov --

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