[Johnson] 250-39 TR switch.

Peter Markavage manualman at juno.com
Thu Oct 23 22:52:15 EDT 2008


They also provide about 6 db's worth of receiver gain between 3.5 and 29
MHz. I've never seen any "suckout" issues that you describe with the
receivers and transmitters/linears that I've run the TR Switch with.
Right now I have one on my Apache/Mohawk combo.

Pete, wa2cwa

On Thu, 23 Oct 2008 22:08:56 -0400 Roy Morgan <k1lky at earthlink.net>
writes:
> 
> 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


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