>
>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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