[Collins] Restoring a Collins 32V-3

[Jim DiMauro]

Jerry:

Your points are all well taken, no dispute with any of
them.  It comes down to a matter of personal
philosophy; mine has served me well over the years, as
I'm sure yours has served you well.  I believe in a
less extensive pre-emptive strike.  Baselining a radio
is something that I (and probably a great many others)
do when I think the radio is ready for the road: take
and record voltage and resistance measurements; they
not only establish reference points that are helpful
in future servicing efforts, they can also identify
some of the very issues you raised with regard to
improper grid bias, drifted resistors, etc.  Depending
on what I uncover during the baselining process, I may
replace additional components, but that's as far as I
normally go.  Admittedly, my approach is potentially
more time consuming and requires periodic check-ups,
but that's the nature of living with boatanchors.  I
just don't do wholesale component replacement, never
have.  To the extent possible, I'd rather preserve
than emulate.  Then again, I've been at this for only
36 years, so I'm still learning :-).

73,
Jim

--- Gerald <geraldj at ispwest.com> wrote:

> On Fri, 2005-12-16 at 08:10 -0500, Bruce H McIntosh
> wrote:
> > On Thu, 2005-12-15 at 22:23 -0600, Gerald wrote:
> > 
> > > Very likely, every paper capacitor (whether
> waxed or molded) will have a
> > > lot of leakage current. They will need to be
> replaced. Every
> > > electrolytic capacitor will be even worse and
> will need to be replaced. 
> > > 
> > > Resistors of that age will have drifted so each
> should be checked
> > > (taking into account circuit connections that
> modify the resistance
> > > reading) that its within the original tolerance.
> Age, humidity, and heat
> > > makes carbon composition resistors rise in
> value.
> > > 
> > > Depending on storage conditions, transformers
> can have excessive leakage
> > > from moisture absorbed in the paper insulators.
> They can be dried gently
> > > in ovens or by running current at low voltage
> through the windings. If
> > > wet insulation breaks down from applied voltage,
> it has to be replaced.
> > > Drying won't remove the carbon tracks from that
> arcing.
> > > 
> > > Then there will be raspy potentiometers and
> variable capacitor wipers.
> > > Cramolin makes products that help them. Some
> will be too bad to be
> > > helped and will have to be replaced.
> > >  
> > > And the most fragile components, the tubes. Some
> will be weak, some
> > > worse.
> > 
> > So, from this litany of woe, one can surmise that,
> unless someone else
> > has already done the restoration before one buys
> it, the purchaser of a
> > boatanchor is essentially purchasing a chassis,
> wiring harness, and if
> > lucky a properly-strung dial cord. :-)  Makes this
> whole "old radio"
> > thing just a trifle off-putting, doesn't it? :-)
> > 
> > (Thomebdy pleeth hand me tht cwobrar; my tongue
> ith thutck in my cheek!)
> > 
> Many of the resistors survive such a restoration.
> Leaky coupling
> capacitors will take out tubes by upsetting the grid
> bias (driving it
> positive). Tubes are more expensive that Orange
> Drops these days.
> 
> Electrolytics age whether used or not, but age
> faster when NOT used. And
> when they relieve excess pressure by blowing their
> guts into the radio,
> the cleaning process can be very difficult. All the
> contents are
> conductive, thin aluminum foil, crepe paper
> saturated with conductive
> electrolyte, and that electrolyte. Sometimes
> electrolytics give warnings
> by hissing, sometimes they just blow.
> 
> The paper capacitors used in 32V vintage radios were
> junk when they were
> put it. They haven't improved with age. They have
> gotten worse. Leaky
> bypass capacitors lower screen voltage (when they
> are the screen bypass
> capacitors) and lead to low stage gain. And they
> increase the power
> dissipation in the screen dropping resistors when
> tends to make carbon
> composition resistors increase in value dropping the
> screen voltage and
> the stage gain further.
> 
> In my experience (been fixing radios since before I
> was licensed 50
> years ago), shotgunning paper capacitors saves much
> trouble shooting of
> marginal interacting failures. Especially when the
> paper capacitors were
> the old color coded black beauties, waxed, or other
> molded papers
> including those that are flat much like large
> postage stamp mica
> capacitors. Mica and ceramic capacitors can fail but
> I've not
> experienced the 95% failure rate of oiled paper
> capacitors.
> 
> The wiring harness can be fragile with the
> insulation falling off each
> wire moved.
> 
> Good soldering tools and tools can emulate the
> factory gal. She had to
> learn to solder once upon a time then doing thousand
> of solder joints a
> day, she got good at it. You can too, but practice
> on something other
> than the radio needing restoration.
> -- 
> 73, Jerry, K0CQ, Technical Advisor to the CRA
> All content copyright Dr. Gerald N. Johnson,
> electrical engineer
> 
>
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