[Amps] SHV connectors great, but where to find coax?

[Jim Thomson]

Date: Mon, 13 Sep 2010 13:45:02 +0100
From: "Dr. David Kirkby" <david.kirkby at onetel.net>
Subject: Re: [Amps] SHV connectors great, but where to find coax?

On 09/13/10 07:18 AM, Roger wrote:

> What we do have to remember though is we may not always be around.  Some
> one other than us may end up moving things.
>
> 73
>
> Roger (K8RI)

Exactly.

I assume none of the people proposing using PL-259 plugs for HV are chartered 
engineers. The Engineering Council in the UK would I expect strip someone of 
their CEng status if an individual proposed such silly things. Even if you do 
this at home, you are putting the lives of others at risk.

  * Children might accidentally get into the shack and unplug a cable.

  * You might have an accident, an ambulance called, and they need to remove a 
cable. I expect they would switch things off before touching electrical 
equipment, but would not reasonably expect a cable to be alive when powered off, 
which will happen in this case due to the time for the HV capacitors to discharge.

##  which is why all broadcast TX in Canada, with lethal B+  voltages inside em now have to
have a warning label on the outside.   "wait 5 x mins for HV capacitors to fully discharge, before
opening cabinet".   That's on top of the inetrlockS  to short the B+  DIRECTLY to the B-. 

## There are also other warning labels..like  " more than one live AC circuit inside"    That's a good one
actually.   I have  a 2nd  240 V dedicated line  going inside  some cabinets.   At work, we would have several
differnt feeds going into one cab... and the same deal... they ALL  have to be shut down 1st.  " This cabinet
contains four live AC feeds". 

##  I 1st heard of folks using PL-259 /S0-239  for  B+ back in the late 70's.   It was a real stupid idea back then,
and it's still a stupid idea now.   I was gonna do it myself, years ago..and thought the better of it.   I could just
see myself, reaching in behind at 2 am,  after drinking too much grog... and unplugging the wrong cable. 
Heck, 99%  of your ham friends would assume that all PL-259/SO-239's they see are for RF.  What IF  one of your
buddies died, cuz of it?   That alone could be reason enough for legal proceedings.   I got whacked from a 4 kv
oil cap, that had no bleeder on it, back in 1976.  The B+ supply had been shut off for 5  days too. ..and NO  HV meter !
That threw me 8' across the room.  I woke up a few minutes later.   One fellow at work got electrocuted, when the
spinner wire he was using broke,flipped up, and hit one leg of a 25 kv 3 phase feed.  Died instantly.  The 500A  air breaker
never did trip.  You don't even want to know what it did to him. WCB handed out huge fines to the co  because of this. 
Turns out he was supposed to have been 3M away from the 25 kv line..not 1M.  

###  One old ham here in town, and a co-hort, were working on a Commercial high power TX..and were drilling holes into
a cab, for mounting brackets.   The drill bit was way too long to start with... and the steel was hard, so he leaned on it good. 
When it finally went through, it slammed into the main B+..which was  12 kv.  He was sitting on a concrete floor.  Another
death.  That was 1968.  Workmens comp board goes crazy when stuff like that happens. 

##  Those alden  HV connectors don't look safe either.  If you trip on the HV cable, the mating plug will pop right out.  The
Red Millens are a death trap also. 

##  Bill's  idea of using a  HV  connector  at the HV supply end is a good one.    Then hardwire the other end of the cable
directly into the RF deck.   That would save one SHV connector pair.  In an ideal world, a SHV connector pair at both ends 
of the coax cable would be optimum. I'd slide some RED heatshrink around the coax at each end..say 1'... and some more in 
a few places in the middle of the same HV coax..depending on length.  With my  Iuck, I'd chop some coax out with heavy duty
cable cutter's..thinking  RG-58/59 is just some feedline for the dud beverage ant.   Any HV cable should be tagged at each end,
and also in the middle of the run. 

## Ian is  correct though.   IF the RF deck chassis  and  HV supply chassis are not bonded
together... and B+ hits the RF deck chassis.... it will be hot..esp if the cab is sitting on rubber casters.  IF  you ever sold
some HB gear.. and the fellow you sold it to, subequently re-sold it again..then ham #3 gets zapped,  you would have
to live with your Fubar, hip pocket engineering  talents for the rest of your life.   Why spend 1-5 thousand $$$ on
a HB amp....then cheap out with the HV connector?    Either hardwire both ends, or at least use the correct connector
on the HV supply end...and preferably both ends. 

later... Jim VE7RF      


There are a number of "unlikely" but probably fatal circumstances in which this 
would be an issue.


Dave