[BC] Transmitter Safety

[R. V. Zeigler]

Dale Adkins wrote:

Ok....one more story, then I have to get some work done.

Have you ever been called about a transmitter that won't go off. !?

How about a transmitter that came back on by itself AFTER you shut it 
off and opened the breakers? Jay White who works for Morris Comm. in 
Palm Springs can attest to this one. We were checking out a 
transmitter site at a newly purchased property and wanted to look 
inside the FM 25 K. We dutifully threw the breakers to the HV supply 
(3 separate 100A in the main panel) and started walking towards the 
cabinet. Jay went to the front, and I started to open the back door. 
We heard the generator come on, and Jay noticed that we had 4.5KV 
showing on the meter! We backed way off and started studying the 
kluged circuitry external to the cabinet.
The previous "person in charge of transmitter repair and maintenance" 
had modified the machine to work at half power on single phase! When 
power was lost to the transmitter, the single phase generator started 
that fed an external HV/rectifier circuit as well as powering an 
outboard blower.(we wondered what that was for)
It also explained all of the other "circuitry" that was built inside 
of a small bookcase behind the rack. After we killed the generator, 
the transmitter finally died, and allowed us to see the wonderful 
modifications done to the inside of the box as well as the analog and 
digital control cards. We put everything back together, turned on the 
main breakers, and let the thing run "normally" while we decided it's 
fate. It took 2 engineers a week of down time, and multiple shipments 
from Harris to put the box back together correctly, with needed 
repairs and upgrades. After that, it was a very stable machine.
One sign on the HV cabinet stated "Bleeder resistors have been 
removed. Use shorting stick when working inside" NO KIDDING!
Rod



-- 
R. V. Zeigler, Dir. of Eng.
Nebraska Rural Radio Assn.
KRVN-KTIC-KNEB   1007 Plum Creek Parkway
Lexington, NE. 68850-0880