[BC] BT-20-A

[nakayle@gmail.com]

I assume this was part of "5K1".   I don't recall this happening with
our 50H which was similar but we did have a lot of problems with 5K1
and it's various trip and reset coils.  But the 50H did have levers
that shorted the 15-KV bus whenever a PA door was open.  The most
dangerous part of that transmitter was the capacitor bank.  Power dips
would often blow one or more of the fuse-wires on the HV caps.  There
were spring loaded plungers on each that were suppose to short the cap
if the wire broke but they often didn't work.  First thing I always
did when I opened the rect cubicle was ground each of those caps with
the stick- and very often I got a arc that sounded like a shotgun
going off.  And you had better keep a ground on them while you
replaced the fusewire because those suckers would build back up a
charge just from 'memory' effect.

-Nat Kayle


On 3/29/07, gRAdy Moates <lists at loudandclean.com> wrote:
> Just a quick note. . .
>
> I saw a man come within 2 inches of dying because of a similar
> relay on a BTA-50G 50,000 Watt transmitter.  We were trying to
> find and fix a problem, and had cycled the transmitter completely
> off, filaments and all.  We had been working for hours, and the
> guy had skipped the shorting stick procedure this one time.
>
> He touched the control grid ring on one of the PA tubes and
> felt a "tingle", so he grabbed the shorting stick and brushed
> the tube with it. . .
>
> . . .and drew a 2" arc from the anode!!
>
> Even though the entire transmitter was shut down, the
> "ReClosing Relay", which actually connected primary 480V
> 3-phase power to the HV supply, was physically stuck in the
> "on" position, and the tubes had full plate voltage on them!
>
> That relay was so unreliable, even after rebuilding by the
> Boston GE Apparatus Service Shop, that we had to add a
> step in the shutdown procedure in the remote control that
> would energize the overload relay to force the ReClosing
> Relay to open.
>
> Grady
>
>
>
>