[BC] Cost of maintaining older transmitters...

[Burt I. Weiner]

I certainly would not include the replacement of reactors of any type 
in the same league as tube replacement.  I have been maintaining 
older tube type transmitters for many years, some more than 50 years 
old.  Reactors and mod transformers rarely go and when they do it's 
usually from some form of abuse.  PCB issues aside, capacitors 
usually last a lifetime.

My opinion, any you know that everybody has one, is that the biggest 
problems I've seen in older transmitters are mechanical devices such 
as motors and mechanical timers.  But then again, SS rigs also have 
blower motors.  Tubes are the major expense but not necessarily an 
overwhelming expense.  Primary power to output power efficiency is of 
course an issue.  I like forgiving and reliable also.

I've been doing NRSC measurements since the day the annual AM NRSC 
proof requirement began.  One of the things that is becoming a 
problem is that in SS transmitters more than three or four years old, 
the electrolytic filters start to cause problems.  This typically 
shows up as the mask spreading out and spurious signals outside of 
the modulation mask.  Mix products between stations has also been 
traced to defective filters in some transmitters.  I've seen where 
shot-gunning the SS transmitter's filter capacitors has resolved a 
lot of strange problems.  These capacitors are not cheap and in some 
cases cost more than several sets of new tubes.

Classic, older tube transmitters are generally more forgiving of 
hostile environments than many of the "newer" SS rigs.  They can be 
more forgiving of load variations.  This is mainly due to the 
impedance transformations associated with the final stage.  High 
Voltage attracts dirt.  I've seen some pretty filthy SS rigs that quit.

All transmitters, SS or tube, need to be properly and regularly 
maintained.  SS rigs cannot be installed, turned on and ignored any 
more than a tube rig.  I know that a lot of people will argue that 
but I see the results on an almost daily basis.

I do not wish a MW-50 on anyone.  Well, maybe I can think of one or two.

Burt

At 10:00 PM 2/21/2007, you wrote:

>Robert,
>    This may be a stupid statement to make, but small stations should not
>worry about maintaining a tube TX for a backup. As you have pointed out,
>one must still perform routine maintenance on these tube boxes to insure
>that if there is a major problem with the main solid state box, the tube
>rig will be there to take on the load. The high cost of tubes, reactors,
>mod transformers, and just older designs are just not cost effective to
>maintain as an aux.
>    I feel with Solid State rigs as stable as they are today, there is no
>need for a tube box at a small stand alone AM or FM. If an AM stand
>alone like mine feels compelled to have a back up, buy the little 250
>watt Energy Onix box, but really, I feel that's not necessary.
>
>Scott

Burt I. Weiner Associates
Broadcast Technical Services
Glendale, California  U.S.A.
biwa at earthlink.net
K6OQK