[Amps] Best source for Gigavac GH-1 ?

[Vic K2VCO]

Interesting point about the 'speedup' circuit. I am using a vacuum relay in series with a 
reed relay in a circuit similar to the Measures circuit. The voltage across the relays is 
normal when measured in a steady state condition, but the open circuit voltage supplied 
through a dropping resistor is higher. The idea is that the filter capacitor in the power 
supply discharging through the dropping resistor and relay coils provides the 'goose', as 
you call it.  Now I'm thinking that this may not be such a good idea. I have used similar 
circuits over the past 15 years or so and only once replaced a relay, due to the receive 
contact becoming unreliable.

I admit to not worrying about the sequencing, depending on my K3, which provides a 
reasonable delay of about 8 ms before and after producing RF.

For contests, I operate the K3's PTT from a Winkey device. This outputs CW directly from 
the computer and generates a PTT signal that holds during CW generation but drops quite 
quickly after the transmission finishes. That way I don't have to use the semi-QSK in the 
transceiver, which will stay in transmit longer than needed. I save the full QSK for 
pileups.

On 11/10/2013 6:58 AM, Jim Garland wrote:
> 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
>
>
>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Larry Benko
>> Sent: Saturday, November 09, 2013 11:38 PM
>> To: amps at contesting.com
>> Subject: Re: [Amps] Best source for Gigavac GH-1 ?
>>
>> Jim,
>>
>> What is failing on the relays?  Is it the coil opening up, the contacts
>> sticking, the receive side contact appearing open, or the pivot getting
>> sloppy and the contacts bouncing too much?  I have tested many relays
>> for mechanical life (low current in the contacts) in previous employment
>> and many exceed 20 million cycles.  All the relays I have tested were
>> made by reputable manufacturers and were generally tested at about a
>> 15Hz rate.  In a well designed amp guaranteed to not hot switch driven
>> with the proper coil voltage the life should be very close to the
>> mechanical life.
>>
>> There is a problem using a relay as a T-R  device where the receive side
>> of the contact sees only very low current (gold plated or gold flashed
>> contacts are best) and the transmit side sees high current (definitely
>> not gold plated).  The dilemma is what type of contact material to use.
>> Generally the high current side rules and the low current side may need
>> a bias current to be reliable.  Often using 2 relays in parallel or
>> bifurcated contacts will give the desired reliability.
>>
>> 73,
>> Larry, W0QE


-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/