John Higdon wrote:

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.

That is, in fact, why I was posting. It looks like they are just changing
the screen grid bias, so I could imagine some situations where that could
be the case.

I am assuming that if I really wanted to reduce the power, the sane thing
to do would be to reduce the B+ voltage to the final?

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.

Yup. I was hoping to find someone old enough to remember setting these
things up for regular use. I dragged this one out and started cleaning it
up because the 160 MHz auxiliary channels are totally unused in our area,
and the 950 Mhz stuff is very crowded. And you know, this thing doesn't
sound bad. Down 3dB at 8 Khz which may be a transformer issue.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article ,
(Scott Dorsey) wrote:

I am assuming that if I really wanted to reduce the power, the sane thing
to do would be to reduce the B+ voltage to the final?

Of course, there are numerous ways to trim the output stage power.
Adjusting plate voltage is one, but to avoid over-dissipating the
screen, both screen and plate voltage should be adjusted together.
Another way is to adjust the loading, as you mentioned earlier. Due to
those "sweetspot" considerations that I mentioned, the loading should
only be used for minor power adjustments during operation. As I'm sure
you are aware, stage tuning and loading go hand in hand.

Yup. I was hoping to find someone old enough to remember setting these
things up for regular use. I dragged this one out and started cleaning it
up because the 160 MHz auxiliary channels are totally unused in our area,
and the 950 Mhz stuff is very crowded. And you know, this thing doesn't
sound bad. Down 3dB at 8 Khz which may be a transformer issue.

We're using the 160MHz channels in our area as well, since everyone else
went to 450MHz. But I've only had to deal with RPU gear in the past ten
years, so I missed the joys of Marti tube gear. FWIW, the very first
piece of auxiliary broadcast gear I ever laid hands on nearly forty
years ago was a Moseley PCL-303. It was solid state, of course, and back
then transistors that could operate at 950MHz were still considered
magic.

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

John Higdon wrote:
We're using the 160MHz channels in our area as well, since everyone else
went to 450MHz. But I've only had to deal with RPU gear in the past ten
years, so I missed the joys of Marti tube gear. FWIW, the very first
piece of auxiliary broadcast gear I ever laid hands on nearly forty
years ago was a Moseley PCL-303. It was solid state, of course, and back
then transistors that could operate at 950MHz were still considered
magic.

So what is the current licensing status on these? Do I need to get an
auxiliary license added to the station license like with the STL, or do
I just call the local frequency coordinator and ask to book the frequency
for certain days? I remember this being covered on the first phone test
but a lot of things have changed since I took the test....
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article ,
(Scott Dorsey) wrote:

So what is the current licensing status on these? Do I need to get an
auxiliary license added to the station license like with the STL, or do
I just call the local frequency coordinator and ask to book the frequency
for certain days? I remember this being covered on the first phone test
but a lot of things have changed since I took the test....

Yes, those must be licensed for routine use. The difficulty in doing
that will depend upon where you are located. Here in the San Francisco
Bay Area, the channels are packed. Even use of a licensed channel
requires spot coordination by anyone planning use that might spill out
of his immediate service area.

The bottom line is it needs to be licensed and you need to coordinate.

Read Part 74.

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