Dick Erhorn wrote:
>Re: Recent discussions about RJ-1A vacuum relay speed of closure and
>possibility of output T/R hot switching in ALPHA 77Dx/Sx and '78 amps. Here
>are some inputs that may help interested parties draw their own
>conclusions:
>
>In the 77Dx/Sx the vac relay coil is driven from ~56v nominal source via a
>simple RC "hot-shot" network, to apply an ~2x nominal voltage spike for the
>first few ms (during contact closure). It then decays to ~20-22v under
>steady state key-down to keep relay coil dissipation nominal. 'Scope tests
>during development measured ~1 ms nominal "make" time followed by ~1-2 ms
>of detectable contact bounce, and ~1-3 ms break time as I recall.
? My measurements indicated a shorter period of contact bounce for both
relays. . With a 110v.oc current-limited source, neither relay fully
closed in under 1.7mS.
> With the
>Jennings RJ-1A contact structure, further increasing the initial "hot-shot"
>closing voltage resulted in significantly worse bounce. These tests were
>repeated many times with different relays from multiple batches.
>
>'The '78 vacuum T/R relay coil is similarly driven via an RC from an
>~30-35v source, and showed ~2 ms both ways.
>
? Do you mean 2mS for initial make and 2mS of bounce?
>Our measurements on popular xcvrs over the past 10 years or so (e.g.,
>TS-940, TS-950S/SD/SDX, FT-1000D, IC-781) found the shortest delay between
>T/R relay external contact closure (to actuate the amp T/R) and output of
>initial RF to be ~7 ms. If I remember correctly the 950 was much longer.
>
? Owners of FT-1000Ds have reported seeing RF output at 5mS.
>Going from T to receive, of course, you don't want the amp relays to move
>until xcvr rf output has disappeared,
? How could such a thing happen if the transceiver keys the relays in
the amplifier?
>and receiver recovery..........
>
>However, at the time those amps were developed there were few to none
>full-QSK xcvrs. ......
? I don't see hotswitching as strictly a CW issue. Even when using PTT
or Lock-to-Talk, some transceivers begin producing RF in less than 6mS
after the switch is pressed.
>Because of the unpredictability of xcvr T/R sequencing and timing, the
>ALPHA 77Dx/Sx and 78 share the same basic electronic T/R interlocking
>system: the amp T/R system is inhibited from changing state (either way - T
>to R or R to T) if RF drive exceeding 20-50 milliwatts (~1.5v @ 50 ohms) is
>present at the input connector. If initial rf arrives before the T/R relay
>closes, it "locks out" - doesn't close. If drive rf is still present when
>the external T/R line to the amp opens, the T/R relays don't open until the
>level drops below ~50 mW. (For smooth and safe QSK with xcvrs OR rcvr/xmtr
>combos having unsuitable T/R sequencing, the ALPHAs have an alternate
>keying mode in which the amp T/R line is keyed directly, and it in turn
>keys the xmtr/xcvr. This system works well enough in the thousands of 77s &
>78s sold between roughly 1974 and 1984 (and nearly all still in service)
>that we changed the control from 9 discrete transistors to a chip or two
>and have used it with great success in the ALPHA 91B and now the '99.
? A friend of mine owns a 91B. I hear the roughness on channel as the
RF actuated bias circuit rapidly switches during voice modulation. I can
hear the adjacent channel spitting. Would it not be better to keep the
bias in sync with the RF relays? For those who do not use Lock-to Talk,
I can see no reason to have the RF relays closed and the bias in
non-linear mode. . . Do you use high speed VOX, or do you prefer
Lock-to-Talk?
>
>With respect to vac relays possibly sticking as a result of residual
>magnetism vs. "stiction" in their mechanical contact actuation system: it
>seems to me that residual magnetism would result in the relay sticking in
>the "T" position,
? Surely. To find out what kind of sticking is taking place, reverse
the coil and cycle it a few times. If the relay returns to RX, the
problem was residual magnetism. However, if the relay does not return to
RX, the problem is probably terminal.
>.......
>Finally, yep, I think the RJ-1A and HC-1 are similarly rated for mechanical
>lifetime. But so far as I know they aren't rated for high-speed (keyed
>CW-type) service -
? I have seen no such ratings -- only mS ratings.
> would guess that their most frequent application is in
>antenna feedline selection matrices.
? agreed
>With even a cursory look at their
>respective innards it's pretty obvious that they probably would behave
>significantly differently under repetitive high speed keying. In fact, in
>our tests during development of the 91B/99, RJ-1As keyed in a simple
>hot-shot circuit with steady fast dits - roughly 20 cps - (NO, not Hz -
>closures per second!) frequently experienced mechanical failures within a
>few hours. We never saw an HC-1 fail under those conditions, even after a
>day or more. (At 20 cps, 24 hours is ~1.73 million operational cycles.)
> And as previously mentioned, the HC-1 has far better bounce
>characteristics.
>
>BTW, we didn't expect and weren't looking for relay failures in those
>tests; we were running prototype and beta amps at ~2.5 kW output with 50%
>duty as a fairly strenuous burn-in test of power supply and cooling
>hardware.
>
>Hope some of this interesting to somebody.
>
- It was. thanks, Dick
>
>
>-----Original Message-----
>From: Rich Measures [SMTP:measures@vc.net]
>Sent: Sunday, July 04, 1999 9:38 AM
>To: n4kw@citrus.infi.net
>Cc: amps@contesting.com
>Subject: Re: [AMPS] RJ-iA relay contact-life on CW?
>
>
>
>
>>Rich Measures wrote:
>>>
>>> Does anyone on [AMPS] know of a case where a CW person managed to wear
>>> out the contacts on a Jennings RJ-1A vacuum-relay?
>>> - thanks.
>>>
>>> Rich...
>>.........
>>Hi Rich, not sure what the exact problem of mine was but I lost the
>>relay
>>(RJ1A) during a cw contest. I was using an Alpha 78, which uses a
>>reed relay ahead of the RJ1A.
>
>? My guess is hotswitching did the damage instead of 2-million closures.
> . As I recall, the 78 does not use enough potential to enable the RJ-1A
>to close fast enough to beat modern transceivers. To effect a speedy
>closure of a RJ-1A with a 26v-rated coil (L=0.3H), one needs 100v - 160v
>open circuit, limited to 80mA,.. . This is an easy problem to correct
>-- if you are not averse to soldering.
>
>- cheers, Pete
>
>
>Rich...
>
>R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>
>
>--
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>
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
--
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