[AMPS] RJ1A/RJ1H for Alpha 78

measures measures@vcnet.com
Sun, 10 Oct 1999 20:48:15 -0700


>
>Does anyone have suggestions (aside from not running QSK) on 
>how one can extend the life of the RJ1A vacuum relay in the 
>Alpha 78 amplifier? Our club station has two of these amplifiers 
>both of which seem to have a propensity to "eat" RJ1As on 
>a regular basis. 

   A 26v RJ-1A has a 0.3H coil.   Charging the coil takes time.  Without 
a speed-up circuit, RJ-1As can not switch fast enough to preclude 
hotswitching with modern radios.    To speed-up a RJ=1A relay, start out 
with a supply of 3 to 5 times the rated coil-v -  and use a series 
resistor to limit current in the coil to 80mA.  A complete circuit, 
including an Electronic Bias Switch (ECBS) is available on my Web site.   
Unlike the Alpha bias circuit, this ECBS does not allow the amplifier to 
switch into non-linear bias during transmit.  An easy way to come up with 
the approx +150v necessary to operate the speed-up circuitry is to simply 
half-wave rectify half of the electrical mains.  The circuit for this is 
shown.  

>One suggestion given to me was to substitute an RJ1H for the RJ1A.
>Any thoughts out there on this idea (I am not familiar with the 
>RJ1H)? 

The H version has tungsten contacts instead of copper contacts.  It is 
designed for hotswitching applications in power supplies.  The RJ-1H has 
no RF current rating.  The contact resistance rating is triple that of 
copper contacts.  My guess is that an H will handle about 4A of RF in SSB 
service at 32MHz.  .  

>How about PIN diode solutions?

  With low SWR and without lightning, they reportedly work ok.  
>
>In the meantime, does anyone know of good (i.e. cheap) source for 
>the RJ1A, I want to pick up a spare before one of club's Alphas 
>gets hungry again?

Fair Radio Sales has them for $35, tested with a high-pot.    Correcting 
the Alpha design problems would be a lot cheaper than feeding it relays.  
>
While you have your Alpha opened up for PM, it's a good idea to replace 
the orig. carbon-comp electrolytic equalizers with (more-stable) MOF 
resistors.  If you see any white deposits around the pressure vents on 
the electrolytics, they should be replaced.  

cheers, Mike

-  Rich..., 805.386.3734, www.vcnet.com/measures.  


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