Antenna delay

[Detroit47]

I am building my myself a 3cx3000 amp. I want to put a delay on the antenna. My aim is to have the antenna relay close first and open last; so as to prevent any arcing. I have an RB2 vacuum relay for the antenna so this will be over kill. I am open to ideas as to how to do this. I have my cathode bias set up as a shunt regulator with switcable voltage so I can change operating class.

73 N8QPC

[WA1GFZ]

I'm working on my 4CX3000A amp this week and just mounted an H8 vacuum relay yesterday.
I was thinking a series diode with a cap across the coil so it pulls in fast and delays drop out.
My bias is a string of 5 volt 10 watt zeners in TX and 50K 10W in RX to cut off the tube.

[W2PFY]

On the Johnson desk KW there was such a circuit. It used a cap, DC source for the relay and a pot for adjusting the delay when opening the ant relay. This has been discussed here on AM Fone in the past.

Don't know if it's in the archives or not? I thought I had the manual on this computer.

Mayhaps someone will know where to find it?

[Detroit47]

On the Johnson desk KW there was such a circuit. It used a cap, DC source for the relay and a pot for adjusting the delay when opening the ant relay. This has been discussed here on AM Fone in the past.

Perhaps I am an Idiot but I didn't come up with anything when I searched the archives.
Thanks N8QPC

[k4kyv]

See Electric Radio #198, November 2005.

[W2PFY]

Look up Desk KW and you'll see some talk about it.

[Detroit47]

Thanks Don

N8QPC

[K6JEK]

I've built Don's design (more-or-less) several times.  It's sequencing everything from a big RCA broadcast transmitter to a tiny class D you can hold in your hand.  In most cases little DIP relays are used to control big relays elsewhere because those other relays were already there and had a variety of specs, 115 VAC relays, 28 VDC relays, the gamut.

Almost all relays are asymmetric. Let's see if I can remember this right.  They hold at a lower voltage than the close voltage.  You'll want to play with the resistor and cap values to get the delays the way you like them but even with tweaking you'll end up with a little syncopation, the open delay is longer than the close delay. No big deal.

I've said this before, clever design, Don.  Here's the DIP version.  Note sequence is Class E, not tube, drive before B+ not the other way around.

[WQ9E]

Since you are already using a vacuum relay for antenna switching, it is going to close faster than the other relays anyway.  All that is required for delay on break is a small electrolytic cap across the relay coil.  With my Desk KW I use a vacuum relay for antenna switching and it is powered by a 28 volt DC supply.  I chose a filter capacitor large enough to give a slight delay on break and this has been in use 6 years with no problems. 

My homebrew amp uses a G3SEK "tetrode board" which provides relay sequencing in addition to warm up delay,  protection and metering circuits, and regulated bias and screen supplies.   It was well worth the cost.