By the time the relay starts buzzing the AC voltage is probably up to maybe
70% of maximum and the turn on surge is about over. The buzzing contacts then
will be shorting across the limiting resistor and the current is not nearly
as high as when the surge begins. Still not a good way to do it though. The
d.c. relay method you mention works just fine as does the timer module with an
AC relay.
I guess I have a fascination with those solid state devices as I use a timer
to activate a 40A solid state relay to perform the "shoring duty". A small
10A ssr is used for initial turn on and the 40A unit shorts around the limiting
resistor and the small ssr. I have had no stuck relay death traps since
switching to the Solid State units.
Most of my amplifiers (vhf/uhf/shf) are tetrodes. They all have a screen
grid trip circuit that opens the ptt circuit, killing the screen voltage as
well
as opening up the control voltage to the Solid State relays so the plate
voltage is also killed asap.
73/k5gw
In a message dated 8/12/2005 4:21:54 P.M. Central Standard Time, r@somis.org
writes:
On Aug 12, 2005, at 10:42 AM, TexasRF@aol.com wrote:
>
> An interesting characteristic of an AC relay is that it buzzes like
> crazy as
> the voltage ramps up to the value it needs to fully operate.
That's why a DC coil relay is needed for step-start.
> I assume that
> the relay contacts are doing that as well which probably doesn't hurt
> anything.
Does hotswitching @ 60Hz sound okay to you?
>
> If the tube has a directly heated cathode, the filament typically has
> about
> 1/10 resistance cold vs. hot. The limiting resistor would be a big
> help in
> reducing the filament current at turn on and that is a good thing.
>
> Solid state timers are available from Grainger for about $20, and are
> adjustable over a wide range of times. They simply connect between one
> of the relay
> coil terminals and the AC supply voltage; could not be easier to
> install and
> work perfectly.
>
> 73/K5GW
>
>
> In a message dated 8/12/2005 12:21:11 P.M. Central Standard Time,
> theo.bellamy@spirittelecom.com writes:
>
> silly me .... that works with a B+ supply, but probably not with a
> filament
> xmfr. Sorry ....
>
> Theo
>
> -----Original Message-----
> From: amps-bounces@contesting.com
> [mailto:amps-bounces@contesting.com]On
> Behalf Of Theo Bellamy
> Sent: Friday, August 12, 2005 1:00 PM
> To: amps@contesting.com
> Subject: Re: [Amps] Soft Start
>
>
> Why not just put the soft start relay coil across the primary. Since
> there
> will be a big voltage drop across the step start resistors - leaving
> very
> low voltage across the transformer primary until the filters charge -
> the
> relay will be timed "naturally". This will also protect against an
> open step
> start resistor since the relay won't ever fire in that case.
>
> Theo K4MO
>
>
>
> -----Original Message-----
> From: amps-bounces@contesting.com
> [mailto:amps-bounces@contesting.com]On
> Behalf Of Rich
> Sent: Friday, August 12, 2005 12:21 PM
> To: Amps
> Subject: [Amps] Soft Start
>
>
> OK guys I made the subject soft start , but that about the only thing
> right this time. The resistor should be big enough , 50ohms 100w. It
> all worked one part at a time but when I hooked it all up together my
> 60
> main power relay chatters , I am going to rewire and not run the coil
> supply for the 60 amp through all the relays. I have the 120- control
> voltage daisy changed the coils and I think I am getting VD. That aint
> good.
> I am able to adjust the delay as required from .15 sec to 180 with
> the
> Dayton relays so ignore my original statement about 10sec delay on
> HV, I
> will adjust it.
> More when I know more.
>
> Rich , kd0zz
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>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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