[Amps] Best source for Gigavac GH-1 ?

Carl km1h at jeremy.mv.com
Sun Nov 10 13:05:27 EST 2013

What is a good relay to hot switch 2000-4000 VAC on a PS that just has the 
cap filter bleeder load? Time isnt important (-;


----- Original Message ----- 
From: "Jim Thomson" <jim.thom at telus.net>
To: <amps at contesting.com>
Sent: Sunday, November 10, 2013 11:39 AM
Subject: [Amps] Best source for Gigavac GH-1 ?

> Date: Sun, 10 Nov 2013 07:58:21 -0700
> From: "Jim Garland" <4cx250b at miamioh.edu>
> To: "'Larry Benko'" <xxw0qe at comcast.net>, <amps at contesting.com>
> Subject: Re: [Amps] Best source for Gigavac GH-1 ?
> ##  the correct device to open off B+  is a vac contactor..... but alas, 
> they
> are way too slow anyway.  The gigavac GH-1 is a superb relay..and way 
> better
> built than either the jennings RJ1A   or kilovac versions.   Most GH-1s 
> will easily
> hi pot test to 7500 vdc  and higher.  Note, you can get em in either 12 
> vdc OR
> 26.5 vdc coils.   So if you are voltage limited...and want to use the typ 
> speed
> up circuit....like a RC hotshot setup...  which is just an overvoltage 
> on the coil,with
> a drop resistor plus cap across the drop resistor, then its easy to do.
> ##  I changed the simple half wave rectifier ..which is 27 vdc, on my 4 x 
> drake L4B
> amps  to a FW doubler..and ended up with 63-67 vdc no load.   That’s 
> plenty
> for even a 26.5 vdc vac relay coil.  Even alpha used only 35 vdc  + a RC 
> hot shot
> circuit on their older amps....using a 26.5 vdc coil.   But the 12 vdc 
> coil on the
> gigavac GH-1  works superb in qsk mode..with as little as 18 vdc, drop 
> resistor,
> and cap across the drop resistor.
> ##  Yrs ago, Kilovac informed me that their results of using the typ speed 
> up using an
> overvoltage + drop resistor on some of their relays.  They also informed 
> they had also
> tested the 12 vdc coil versions of their relays in the lab....and 
> mentioned the 12 vdc
> coils were a good option for folks who are stuck with only 26 vdc..and 
> still want QSK/.
> ##  BTW, the gigavac G2 and G2 ham  relays  will also run full qsk with 
> the RC hot shot circuit.
> They are rated at 15 msecs operate..and  9 msecs  rls.  When sped up with 
> 130 vdc on their
> 26.5 vdc coils..and  using a .5 uf cap across the drop resistor, BOTH the 
> operate and rls times
> are  2.5 msecs.  And as high as 2.7 msecs  for the 2nd relay we had 
> tested.   And that includes contact bounce
> too.   The G2  is rated for 10A  CCS  at 32 mhz.  Parallel  2 x G2s....and 
> then its good for 20A at 32 mhz.
> That’s  20 kw CCS  at 32 mhz...into a 50 ohm load......AND qsk too!    The 
> paralleled vac relay concept
> works very good.  3 x relays in parallel was also tested..with superb 
> results..and a 30A at 32 mhz rating.
> Of course the V rating wont change, but the peak V rating at 32 mhz and 
> lower is already sky high  vs
> the smaller GH-1 .
> ##  Just sequence the entire mess correctly.  I also use high swr 
> protection on the amps, via
> the array solutions wattmeters..set for 2:1 swr.  I also installed an 
> adjustable spark gap  directly across the vac
> LOAD cap in my hb amps.  Its set to fire at a voltage that is higher than 
> a 4:1 swr.... but well
> below the vac load caps  rating..and also well below the peak V rating of 
> the vac relays.
> ##  How many G41 relays  have you tested??    Something is amiss if you 
> are seeing 20 contact bounces.
> Jim   VE7RF
> Interesting discussion, re vacuum relay failure modes. I've zapped two 
> RJ-1a
> relays over the years, but both times it was my fault. The first time was 
> in
> the 1980s, when I used one as an HV interrupter in a power supply, not
> realizing they're not designed for DC load switching. The second time was 
> in
> the 1990s, when I used one to switch an extra capacitor  in parallel with
> the tune cap  on an 8877 amplifier,  exceeding the relay's voltage rating.
> The failure mode in each case was to weld the NO contacts together.
> I've used RJ1a relalys in QSK circuits for many years, including a half
> dozen contests each year, but nothing like the contest involvement some
> others have reported. During the past year, I've gotten interested in QSK
> circuits for a homebrew project and made many tests on a variety of vacuum
> relays. Most types, I've found are not well-suited for QSK use, either
> because they're too noisy, too slow or, more commonly, have excessive
> contact bounce. For example, the Gigavac  G41, used in the Alpha 9500, can
> take 7-10 mS to settle down and can have twenty or more contact bounces 
> when
> the NO contacts make. The problem, I believe, is that the coil produces 
> too
> much magnetic force on the movable contact and really slams it into its
> mating contact. If the bouncing happens while  hot-switching RF, the relay
> will have a very short life. So-called "speedup" circuits, that goose the
> relay coil with a voltage pulse to accelarate the switching time, can 
> really
> exacerbate the contact bounce problem.  As I mentioned before, the 
> Jennings
> RJ1a appears to be the best relay for QSK use at amateur power levels
> (though I've not checked its Kilovac or Gigavac clones). The RJ1a is not
> only very fast (1-2 mS closing, and 500uS opening times), but has 
> absolutely
> no contract bounce.
> In researching the subject during the past year, I've looked at the relay
> circuits of a number of commercial amplifiers. Most seem to treat T/R
> switching pretty cavaliearly, without adequate protection for the relays. 
> In
> my own design (the circuit mounts on a 3"x5" PCB), I've tried to prevent 
> any
> situation that can damage the contacts. This involves several precautions:
> (1) sequencing the amp so the output relay, bias switch, and input relay
> operate sequentially in that order, after allowing for the relay closing
> times and contact bounce. (2) Having an RF "lockout" sensor that prevents
> the amplifier switching sequence from beginning if RF is present on the
> input line. (3) Having an RF "lockon" sensor that keeps the relays closed 
> so
> long as RF is present. My new amplifier completes its T/R switching in 4 
> mS,
> which is suitable for QSK speeds up to about 60 wpm, far beyond it's
> builder's capabilities.
> 73,
> Jim W8ZR
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