[BC] Are there AM stations still using Tube Rigs?

[Xmitters at aol.com]

In a message dated 3/21/2009 9:46:23 PM Central Daylight Time, 
broadcast-request at radiolists.net writes:

> I have a quick question, are there many small to medium size AM stations 
> still using tube transmitters as a main transmitter? I only know of 1 in the 
> market we are in, and it's held up since about 1960, still on the air with 
> daily service.
> 
> The reason why I ask is because the tube transmitters can tune into loads 
> that a solid state, like my BE can not. I called be BE and they wanted nearly 
> $2,500.00 for a output network to go with my AM1A. I contemplating on finding 
> me a latter model tube transmitter that is solid state up to to the finals, 
> that has an output network. 
> 
> Tubes have the warmer sound that the typical solid state 1 KW don't have. 
> The only good part about them is the solid state is more efficient, vs. the 
> tube rig, and of course, the power bill, along with buying final tubes yearly. I 
> may bave to break down and just buy the output network from BE.
> 
> Scott 
> 
> 

Scott:

I'm sure there are many stations using tube transmitters. One station I know, 
a 5 kW directional, uses a Collins 820E, which uses two 4C5000A in a  class B 
modulator and 1 4CX5000A in the PA; conventional plate modulation. Since that 
rig was installed in 1972, I can count the number of failures on one hand, 
and still have fingers left over :-)  The same station uses a 20V3 at night, 
with a similar outstanding track record.

I do have to disagree with you that a tube transmitter sounds warmer than SS. 
There are many, many things that control the transmitted sound quality other 
than the transmitter itself, like audio processing. I would use any 
transmitter if I were allowed to use a patch cord for my audio processor :-)

Regarding your Z match issues, I kinda miss not having Tuning and Loading to 
be perfectly honest. I think it would ultimately be to your best advantage to 
optimize your matching network at the tower, find a phase shift that gives you 
good impedance characteristics across your AM channel, and also present an 
honest 50 Ohms to your BE transmitter. My experience has been that once all of 
these things are set up initially, they do not need daily cranking to keep the 
transmitter happy. 

If you have a wandering load Z on your transmitter, you need to find out why 
it's wandering rather than buying a tube rig or BE's matching network. Getting 
your system load Z stable will be cheaper in the long run. 

Honestly, I do miss the days of replacing tubes, optimizing the 
tuning/loading so the modulator is happy, efficiency is good, plenty of TPO to feed the 
antenna or common point. I used to really look forward to doing that stuff :-)

If you have a system with a constant load, there's not much point to having 
tuning and loading. Remember that SS is not forgiving like tubes. Tubes will 
tolerate a short term piss-poor load that generates more heat than RF. 
Transistors cannot tolerate that, whichis why I'm glad in a way  there's no longer 
tuning and loading. The BE 1 kW is a nice little transmitter. The ones near me are 
like Energizer Bunnies; they keep going and going, or whatever that 
commercial says. You get my point :-)

Jeff Glass
Northern Illinois University
Dell 2650 Win2000 AOL 7.0