Introducing Relay Delay

[w4fms]

On my Globe King 500, I use an external relay to mute the receiver.  The relay I use is the newer sealed type made by Potter Brumfield with a 120v coil.  The GK has terminals on the back to supply a switched voltage from the primary of the HV transformer.  This works well except for one problem.

When I unkey the GK, this muting relay unkeys just a bit faster than the T/R relay in the GK causing just a very quick burst of audio feedback from the receiver.  It's very fast certainly less than a second but irriating nevertheless.

Short of adding another relay to switch the relay, is there an easy way to introduce some delay in my AC muting relay so is will unkey just a little bit slower?

Any input appreciated.

Frank, W4FMS

[WQ9E]

Frank,

Look at the Johnson Desk KW manual (available on Bama) for pretty simple instructions on how to do this.  Basically you are rectifying the AC output and using reduced voltage DC on your relay coil.  A filter cap with resistor across it determines the delay time.  Johnson uses this method to avoid hot switching the T/R relay on break.  I believe this same setup was built into the KW match boxes.

Rodger WQ9E

[Steve - WB3HUZ]

Most 120 VAC relays will work FB on 24 VDC. DC with a cap should provide the needed delay.

[ke7trp]

I have the exact same setup and do not have this problem. However, I do have this problem on my Champion 300. This Globe transmitter uses the same internal realy for the coax switching. I use a Dowkey with it now. Problem solved.

I wonder if the real problem is that the King is staying energized to long after you unkey and not that the PB Mute relay is to fast? 

I have done extensive work on the PTT system in the king with alot of help from some people on the board.  If found that once I replaced the Cap in the modulator deck on the PTT system and used diodes instead of the SRs' I have instant relays. My Cap.. From memory was C39.  It was the wrong value from the factory. check it..

An elecrolytic cap will hold the PB open longer if thats what you want to do.

Clark

[N3DRB The Derb]

all selenium needs to go.  rotten stuff.

[w4fms]

The only selenium that I didnt' replace is the diode feeding DC to the T/R relay in the RF deck.  It was so tight in there, I left it alone.  I did replace the diode and cap  in the mod deck that feeds DC the the HV relay in the PS.  I don't know that replace that diode would make the relay and faster but will try it.  We're not exactly talking about QSK switching speeds with the GK.

Clark..BTW..check out the squirrl cage fan in the new fair radio catalog.  I didn't measure but looks a lot like the fan in my 500C.

Frank
 

[KM1H]

When I had to replace the 3PDT 12VAC plate relay in my 6M NCL-2000 I found it was only available on special order.

So I went with a $2 surplus P&B 12VDC unit and added a little rectifier circuit. Worked fine except the antenna relay was still 12VAC. A little experimenting and found that 3.3VDC was ideal for maintaining the same switching timing.

Since any rig that could handle 12VAC switching went out with the Dodo bird that eliminated that issue during subsequent upgrades.

AC relays are really modified DC relays and I had that proven about 12 years ago when several 24VAC relays used in stacked yagi switching stopped working. Apparently years of RF, or more likely close lightning strikes, affected the core since they now worked perfectly at 24VDC at the published DC current.

Carl
KM1H

[ke7trp]

I will look at the fan now.. Thanks for the tip.

I still think that something is holding your relays in the king open a little longer then the mute relay. This happens in my Globe.  For now, Just strap an electrolytic to the mute relay.

Clark