[Johnson] 250-39 TR switch.

[Roy Morgan]

On Oct 22, 2008, at 9:54 PM, <kb2wig at twcny.rr.com> wrote:

> I'm considering  the acquisition of the Johnson switch.
>
> ? what do they go fer now?
I don't know.
>
> ? who has one fer sale?
Not me.
>
> ? do I really need one?

Probably not.  Here's why:

-The main disadvantage of these things is suckout.  The transmitter  
being attached to the receiver/antenna during receive sucks signal  
from the system.  This may not bother you if signals are strong enough  
and/or your receiver has enough gain.

- A second disadvantage is that they are reported to generate TVI.   
These reports came at a time of 21 mc TV IF frequencies, however.  You  
may have no trouble at all, but good citizenship would call for very  
careful testing and corrective measures if needed.

If you DO get one of the Johnson units:

- They run blistering hot.  Three reasons are higher line voltages  
than in the past, the tube used (6BL7?) dissipates a lot of heat in  
both filament and plate, and just plain inadequate ventilation.  A  
small computer fan located nearby would solve the problem.

- There is no fuse in them as built, and only a two prong line cord.   
The solution to these somewhat dangerous conditions is pretty obvious.

- The instructions say to locate it as close as possible to the  
transmitter.. Apparently this really does matter.

- The instruction sheet is on BAMA as I remember.

Roy


Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073