[R-390] ElectrolytiCapacitors

[Drew Papanek]

Kees wrote:

>I think I've got it, replaced the internals with 3 new electrolytics
>and, since I was a little aggressive removing the internals of
>the old electrolytic (didn't realize how much "tar" there was
>inside),

<snip>

The Official R-390A List designator for electrolyticapacitor internals is 
not "tar", it is "uckumpucky" :)

>found some aluminum tape and it looks pretty good.
>Next time I'll use a razor saw and cut off only the rolled lip
>and "heat" the internals to remove them  ....outside.

<snip>

A hacksaw carefully guided into the radius where can flares out to base 
diameter works well also.  Make one light cut motion, roll the cap slightly, 
make another light cut connecting to the first, roll again, etc.  After a 
few revolutions the saw will start to break through.  Done right, this 
leaves a very even cut square to can's axis.

When can is cut, uckumpucky can be very easily removed.  Do not cut through 
internal aluminum connecting straps yet; these along with base provide a way 
to pull out uckumpucky. Heat can with profane gas torch, keep flame moving 
and heat more around top end of can (do not heat the now loose base).  Wear 
leather work gloves, grip base and can, gently pull base away and uckumpucky 
will come out with it.  Heat more if stuck.  If you overheat, can will start 
to rise off of base on its own, as though posessed and rising from the dead.

If you have lathe access, cap can be opened by facing off rolled edge and 
rubber gasket right down to plastic base.  Metal spacers/shims may be 
inserted between pins for support then pins gripped in vise. Taking care not 
to melt base, apply heat then gently pull can off leaving base with attached 
(semi melted) uckumpucky.

Is the other (non-disumpuckyed) cap made by General Instruments?  If so, 
redo that one before it fails, spewing corrosive goo all over the inside of 
your radio.  The General Instruments caps are much more prone to failure 
than caps of other manufacture; at this age quick failure is almost 
guaranteed.  Resultant B+ short circuit is not a nice thing to do to 
transformer/rectifiers/chokes even in a 3-fuse radio.

>Found a qty of "line to 4-8 ohm" transformers ...apparently
>they work well from 600 ohms to 8 ohms. Gads, I threw away
>about 20+ of them because I didn't know what they could be
>used for

<snip>

Besides the usual audio applications, they can be used as step up 
transformers in bias supplies.  Connect low impedance winding to 6.3 VAC 
filament line, rectify and filter output from high impedance tap of your 
choice.
I did this in the otherwise all line operated Hallicrafters HT-9 transmitter 
to replace 45V bias battery.

Drew

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