[BC] 1 kW AM transmitters, old or new solid state

[Xmitters at aol.com]

In a message dated 3/9/09 4:00:30 AM Central Standard Time, 
broadcast-request at radiolists.net writes:

> KRSN in Los Alamos had nursed along a used MW1 for years, always fighting 
> failing modules, and the new owners (local couple from unrelated 
professions) 
> plunked down the money for a Harris DAX-1, tiny little PWM transmitter that 
> it is. They have only had one problem due to early on failure, and it has 
run 
> for several years without stop. It would trip off sometimes on high 
> modulation peaks due to the crappy match, so they backed off the modulation 
> and it is solid. They keep the limping MW1 for a backup, but it hasn't seen 
> power since the DAX moved into the bottom of the audio rack beside it. I 
know 
> the folks are very happy with their decision, as the transmitter is no 
longer 
> their weak link. 
>  John 

Hi John:

I started out in radio in 1977 with an MW-1 at one station and a BC-250GY at 
another. I got tube and solid state training at the same time :-)

My MW-1 would often run for a year or more without the need for repair. You 
mention the crappy load that the new DAX works into. A bad load will  cause of 
most MW-1 failures. They only like 50 j0 Ohms for a load, and failures 
increased exponentially as you deviate from that impedance. The PA voltage to c
urrent 
ratio had to be right on as well. I checked the MW-1 first thing upon arrival 
for work.

My failures were so few and far between, I had to reread the manual to renew 
my understanding of it. Oddly, most of my failures were in the Audio Driver; 
my positive peak modulation would drop to about 60% with Neg at 100%; we 
usually ran the positive at 120% or a little less. I lost few PA modules by 
comparison. 

I know a lot of members here have worse experience but thankfully, mine was 
quite good. 

Regarding tube stuff, the parts might be around, but getting good tubes 
ESPECIALLY the glass ones, is a real challenge. I would not want a tube AM rig 
unless it used tubes still in use for FM rigs. If you're fortunate to have a ca
che 
of NOS tubes, then this is less of a problem. 

Jeff Glass, BSEE CSRE
Chief Engineer
WNIU WNIJ
Northern Illinois University