[Johnson] 250-39 TR switch.

[Dennis]

I forgot to mention; with the old boatanchors the Electronic TR switch provides full breakin CW operation and on SSB provides click-less switching between transmit and receive when using VOX....

Ciao, Dennis, k0eoo


---- Roy Morgan <k1lky at earthlink.net> wrote: 
> 
> On Oct 23, 2008, at 10:34 PM, Rodger wrote:
> 
> > ... T/R switches are rated for pretty high power that is only true  
> > when the antenna is well matched to the transmission line, that is  
> > low SWR.  Otherwise the voltage the T/R tube sees may be much higher  
> > than it can handle
> 
> Agreed, this could be a problem.  The tube in the Johnson unit is, I  
> think, the 6BL7, a dissimilar dual triode octal tube which would seem  
> to be quite strong at the grid.  Other T/R switches use 7 or 9 pin  
> mini tubes and are likely much less robust against high RF voltages.   
> The RF voltage, RMS  mind you - not peak, can be the SWR times the  
> voltage expected for 50 ohms at the output power level.  Add  
> modulation peaks to that and it will frighten any 6AU6 or 6AK5 you can  
> use!
> 
> I recently got a B&W T/R switch that uses such a small receiving  
> tube.  If I remember right, all B&W transmitters were in the 100 to  
> 150 watt class or below.
> 
> 
> > ...  If you want to experience full break in CW like it existed in  
> > days past and are willing to put up with the drawbacks then you  
> > might want to play with one.  But otherwise a relay is going to be a  
> > better choice.
> 
> Of course there is the sought after state of real QSK.  With  
> boatanchor gear, this usually involves modifications at the receiver  
> and two antennas.  With modern equipment using linears, it's PIN  
> diodes or vacuum relays, or both.
> 
> Sooo many projects, sooo little time!
> 
> Roy
> 
> Roy Morgan
> k1lky at earthlink.net
> 529 Cobb St.
> Groton NY, 13073
> 
> 
> 
> 
> 
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