Dow Key relays for broadcast TX's. Is smoke in my future?

[VE7 Kilohertz]

In all my futzing around with the switching relays in the last few days, and with some of the suggestions from you fellows, I have decided to completely redo my ham shack antenna wiring. I have too many TXs and RXs to keep doing it the way I have been doing it. So, what I am planning is having a big rotory switch in a metal grounded box, to switch broadcast rigs around, and either a multicoupler or smaller rotory switch, like those nice 11 position ceramic wafer switches, and mount that in a nice metal box to switch the RX's, and then have the output of those 2 boxes go to a master T/R relay. I have some Dow Key relays, inlcuding some newer ones that have N connectors and I would like to know if they will handle a 1KW carrier plus some audio reliably, IF, IF I DO NOT HOT SWITCH. i.e. delay the TX on until the relay has engaged and drop B+ before disengaging. I have been running almost that power thru one for about 6 months now with no apparent problem but would like to hear from you, what your experience has been with them.

Does anyone have "official" specs for them? Are there various ratings for different vintages? ie older better or worse. I would rather use these as they are RF tight, already have connectors, and I have them and don't need to build a box to house an open frame relay. They are also quiet.

Thanks
Paul
VE7KHz

[W3NP]

I use a "DowKey" type of relay on my Gates BC-1G and I have never had any problems, even at full rated power. My switching sequence has the antenna relay closed before the TX comes up and the TX step-starts over a 500ms period of time.
I know that Don K4KYV roasted one with his Gates before he changed his start-up system.

[K1JJ]

Hi Paul,

Here's a universal coax switch I found to be a solution to using many rigs and receivers into many amplifiers or AM transmitters.  Lots of choices.

It's the MFJ-1700B. With it you can switch SIX different transmitters to SIX different amplifiers (or antennas).  Lets you pair up anything to anything, so to speak.

I've used it for years now at 1500W, no problem. This is not for 1KW AM applications, but for the low level stuff.  I use it to route my antennas to remote receivers for workshop, etc, and handles all rigs to amplifiers. Quite the box for around $70 I think.  If I remember statistics correctly, that's 36 different combinations of rig/amp or antennas.

Might be a solution for you too, OM.



73,
T

[WA1GFZ]

A dow KEY with aux contacts interlocked with a second relay will give the proper interlock to dry switch. Second relay only closes after aux contacts are made so the aux contacts are in series with second relay coil. Second relay controlls DC power. When the mode changes to RX the dow key needs to stay on until dC power is dropped. This means the dow key coil needs to have power through the second relay NO contacts. (needs to be 2 poles)  The dow key needs it's coil power to come from 2 sources. 1 the key line and 2 the contacts of the second relay both ORed.
This way you can start the process and get the correct interlock. Delay circuits are a pain. Simple interlocks are the way to go KISS. The dow key coil power coming through the second relay contacts can't be the key line it needs to be on all the time. (source side of contacts) 

[k4kyv]

See the article in last month's Electric Radio

[VE7 Kilohertz]

Hi Paul,
Here's a universal coax switch I found to be a solution to using many rigs and receivers into many amplifiers or AM transmitters.  Lots of choices.
It's the MFJ-1700B. With it you can switch SIX different transmitters to SIX different amplifiers (or antennas).  Lets you pair up anything to anything, so to speak.
I've used it for years now at 1500W, no problem. This is not for 1KW AM applications, but for the low level stuff.  I use it to route my antennas to remote receivers for workshop, etc, and handles all rigs to amplifiers. Quite the box for around $70 I think.  If I remember statistics correctly, that's 36 different combinations of rig/amp or antennas.
Might be a solution for you too, OM.
73,
T

Hi Tom,

Wow! That is a beaut! That should keep me going for a while. Too bad they don't make one to handle the 1KW Am rigs.    Would be great for RX's though and like you mentioned, low powered rigs.

Frank, thanks for the tickler on the Dow Key aux contacts. The modern ones I have don't have the aux contatcs but some of the older ones do. Great idea. I found current specs on their web site and they list them at 1KW power CW but they don't say whether that is swicthing power or carrying power. An email to them is in order. The Dow Key delay off can be implemented by using the RC dleay I described in my relay switching post. It works great.

Don, thanks! I just got around to reading the Nov. ER. I am a little behind in my reading. Good article.

The contacts look like they would be good for 5 or maybe 10 amps max, which should handle the 1KW level.

Cheers

Paul

[WA1GFZ]

I don't like RC delays myself. I prefer a good interlock system. two or 3 realys are enough to make it fail safe....  The AUX contacts are small. My solid state rig only needs the aux contacts. I run the coil off a 28 VDC supply and do use a cap to hold up the contacts until the modulator drops out. a Bit JS but worked fine for 10 years.