[AMRadio] BC-1T


cemilton at aol.com cemilton at aol.com
Sun May 13 17:58:04 EDT 2007


I''d like to get K5 if I can find a replacement, don't know the type
yet, however it appears to be an octal plug-in.

I've got other rigs that supply both LV and filament voltage as soon
as they are turn on, however I wonder if anyone has some ideas of why
I would really need K5 in the Gates, that is until I can find suitable
replacement.


GE Brian,

I don't have the schematic for the BC-1T, so my comments are general in 
nature.

I worked on one many years ago, but memories fade.

A good rule of thumb with the old transmitters is that everything from 
start-up to shut-down worked in a sequence.  Albeit pretty much 
mechanical at the time, it worked.  As an example, rectifiers were 
often mercury-vapor types (e.g.-866's) and they required warm-up time.

The engineers who designed these beauties knew that those employed by 
the local stations would be "stars" (aka disc jockeys) first and 
"engineers" (3rd phone ticket with permission to adjust plate voltage 
rheostat only) last.

So they made the rigs as best they could and time-delay was a part of 
their scheme.  I never encountered what we call today, "step-start" in 
these 1kw (often .25kw) transmitters.  But the time delay relays, where 
used, were the next best thing.  For example, they gave the old 866's a 
few minutes to vaporize the mercury before allowing full plate voltage 
to be applied.  Most times it worked.  Other times, when it didn't, new 
tubes were needed.

In winter months, I would leave the filaments on in the Collins 300J 
and 20V-x transmitters so that a cold start the next morning wouldn't 
be encountered.   Remote transmitter buildings were often not heated 
(except by the transmitter) or the heat was turned on only if the 
temperature inside was below 40 degrees (f).  These were cost cutting 
measures used by management as the profit margin of the station was 
usually very slim.

So, in the quest to return old bc transmitters to service I'd opt to 
find and use whatever time-delay devices were called for in the 
original circuits.  Those octal plug T-D relays are still available if 
one looks far enough.  However, if you are modifying the transmitter 
and such things as 866's are but a dim memory..........then review the 
circuit to ensure understanding of what they were there for and then 
omit or substitute based on your new configuration.

Hope some of this helps.   It's just a bunch of thoughts stemming from 
those days when these wonderful transmitters were the backbone of the 
bc industry.

73 de W4MIL
Chuck
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