[GreenKeys] How not to test a teletypewriter

[Randy and Sherry Guttery]

  On 10/12/2010 12:25 AM, tony j. podrasky wrote:
> I DID NOT LIKE messing around with an amplifier that used several
> kilo-volts at around an amp and in the maintenance instructions told
> you to take the "shorting rod", which was a long fiber pole with a
> heavy gauge wire at its end, that was grounded to the frame and touch
> it to the plate before you worked on the unit.
In commercial radio circles - those are sometimes known as 
"Jesus sticks"...  as forgetting to use one can (under 
certain circumstances) cause one to meet Jesus "too soon"...

Here is an example of one in a commercial transmitter...  
and just how "nasty" 15KVs at an amp+ can get...

http://www.comcents.com/rg/mw5.html

What I don't mention in that story with regard to the "Jesus 
sticks" in that transmitter was the fact that at one time we 
had a massive failure in the transmitter because the station 
owner decided to shut the transmitter down for a few days. 
The studio was being re-located - and with the STL out of 
service - the transmitter would be just transmitting dead 
air...  so the guy decided to save some money by shutting 
the transmitter off.  What he didn't realize was that the 
transmitter house had some large vents just under the roof 
peaks - which had exhaust fans blowing out of them.  With 
the transmitter shut down - the fans also shut down 
(including the blower in the transmitter itself) allowing 
rain to blow in through the vents - and into the 
transmitter.  When he tried to fire the thing back up - it 
was spectacular - as the 15KV 1.1Amp supply was thoroughly 
soaked (there was roughly an inch of water standing in the 
cabinet bottom). "Lightning" went everywhere.  Fortunately - 
Harris transmitters are pretty well protected - and the arc 
detect and phase detect circuits all went into emergency 
shut-down before any permanent damage was done.  Took Sherry 
and I a couple of days to dry the thing out, Sherry 
literally climbed into the thing to wipe down all of the 
high voltage components with distilled water and alcohol to 
remove all the muck and carbonized traces from the arcs. 
Obviously - many of the components were completely removed 
(modulator and PA tubes, etc.) cleaned - and then once the 
HV sections were back "working" each section would be 
reassembled and brought back on line.  At one point - just 
the HV was functioning - with no load - so you have 15KV 
with no "bleed" - so the only "bleed off" on power down are 
these two large solenoids whose armatures (which are 
grounded) literally "fall" onto two contacts in the high 
voltage section to discharge them when going from "HV on" to 
standby (or off).  Without a load to bleed any of the power 
before those contacts close - there is one heck of a BANG as 
15KV at a couple of amps are shorted from the main power 
supply capacitors to ground.   OR at least there SHOULD be.  
We found the connections were loose - loose enough that 
sometimes there wasn't any bang.  That's one of those 
"circumstances" where failure to use a "Jesus stick" could 
earn one a quick trip to eternity.  Turns out we found 
several problems in the safety circuits - we suspected 
sabotage by some former "person" (disgruntled tech, 
engineer, whomever); but if not - gross incompetence.  In 
spite of TWO stages of safety shunts on the high voltage in 
that transmitter - because of those issues - at times - only 
the "Jesus stick(s)" stood between someone - and a quick 
death (I've never heard of someone surviving contact with 
that kind of power).  If the device you are working on has 
safety sticks - use them EVERY TIME...  and even if some 
equipment doesn't come with them - but has supplies that are 
more than 100V at 100ma or more - make up your own safety 
stick - and use it!

best regards...

-- 
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
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