[ARC5] Old Dynamotors- Don't be a DooFuss Like Me....

[David Stinson]

You know you're getting old 
when you forget your own advice....

Dynamotors.  They're old.  
Many have been in "hyper-sleep" for 70+ years.  
But things are happening while your dyno sleeps.  
Sneeky things.
Things like humidity creeping slowly and inexorably 
inside the dynamotor's case and snuggling deep 
into the armature and field windings.

I've dealt with this before.  Some of you remember 
that I've even written about this before.
I once poured a little water out of the end bell 
of a warmed-up PE-73; no kidding.
I wrote: 
"Leave the end bells off for awhile when you fire it up
 to drive-away the accumulated moisture."   

So.... 
Here I am refurbing a beautiful 1941 A.R.C. 14-Volter 
dynamotor for the GF-10 / RU-15 project.  
I pulled the end bells, clean, lubricate, 
check the brushes/commutators and 
give it a short spin-up as a prelim-check.  
Then my aging noggin has what is often termed a "brain fart."  
I snugged the end bells right back on 
and proceed to fire-up the refurbished receiver.

Man, it sounds good.  For about 30-40 mins. 
Then... "things"... start to..... happen.
The audio starts to surge up and down.  
Out comes the scope probe.  
Everywhere I put the probe, the voltages
are "wibble-wabbling" in time with the surges.
So I look and sure enough, the B+ is surging.
Then I hear on another receiver the unmistakable 
pip-popping of an arc.  
Oh, crud- Emergency shut-down!

I've already checked and rechecked all the caps and etc. 
in the RU before applying anything more than "tickle me" B+.
Isolated the dyno supply and sure enough- that's the baddy.
After pulling it apart and checking all the stuff in the filter base, 
I walked away for a few minutes scratching 
my now-malfunctioning head.  

After another cup of coffee, that feeble pen-light between my ears
came-on and I experienced another one of those moments 
common to we over-50 fellas:  "Ohhhh Noooo (face palm)."
I pulled the end bells and wiped a finger in them and, 
sure enough, they felt moist.  

I thought about putting the whole thing sans end bells 
into a 200-degree oven for a couple of  hours to dry it out, 
but decided to try air-drying first.  
I let it sit for 3 hours with the end bells off, 
then brought it up slowly.
It was back operating normally 
and remained so the rest of the day.
I knew better, dang it.  One thoughtless moment.....
It was just blind, dumb luck that I didn't blow the armature.

Don't be a doofuss like me. 
Remember- those big'ol dynos ain't vacuum-sealed.  
Pull the end bells and leave them off 
for the first few hours of operation.
Give that dyno a chance to dry or you just might cry.

73 DE Dave AB5S