RadioBanter - View Single Post - Marti M-30B

John Higdon[_2_] · March 13th 10, 08:27 PM posted to rec.radio.broadcasting

In article ,
(Scott Dorsey) wrote:

So questions include: how do I use the switch for tuning, AND once I have
done that, is there any reason not to just leave the switch on TUNE in
order to reduce power and extend the life of the final if I don't mind
the reduced range?

Gee, and I get called an old fogey...I haven't seen tube-type gear in
ages! But seriously, to answer your question: there might be a problem
doing that. The purpose of the "tuning" mode is to limit stage operating
parameters to "safe" levels until proper tuning is either achieved, or
is good enough to allow safe operation of the tube.

You have to ask yourself if the unit, properly tuned, might be better in
terms of efficiency and component longevity in "normal" mode than in the
parameter-limiting "tune" mode. It's a distinct possibility.

Not only that, if I set the antenna coupling for reduced power, is that
going to extend the life of the finals?

It could, assuming you don't kill the efficiency of the output stage.
One of the arts tuning up any transmitting device is finding the sweet
spot in terms of plate current, grid drive, and stage coupling. The
Harris MW-5 transmitters were notorious for having a narrow range of
final plate current and drive. Operate outside that range, and your tube
life drops precipitously, even though from a raw tube-spec point of
view, everything was well within limits.

--
John Higdon
+1 408 ANdrews 6-4400
AT&T-Free At Last