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Electronic Key Interface for Vintage Rigs


Electronic Key Interface for Vintage Rigs

Sometime this past year, I acquired a Jackson Harbor Press KeyallHV kit.  This accessory allows one to key their vintage rig, be it an old tube rig, a hybrid or a more modern solid state one.  It is basically a circuit that isolates the keying contacts from any high voltage circuitry in the rig via an opto-isolator and a set of heavy duty MOSFETS.


Kit assembled

While I like CW operation (especially for contests), and I can copy code at 15 wpm without too much problem, I am a big fan of paddles and keyers of any type that eases the sending of CW.  This includes using a computer to send canned messages typical for a contest contact. A straight key is OK, but I like the modern conveniences for this.

For example, I use the N3FJP log on my computer to log all contacts in contests and for awards.  It has a built in keyer that uses one of the lines of the serial port of the computer to key a modern rig.  I made a simple one transistor circuit built into the 9-pin serial connector to interface it to my TS-480.

Now, say I want to use this capability with my old Heathkit HW-16 CW Novice transceiver… Or my Hallicrafters HT-37 transmitter…

The circuits in these old tube rigs place about 150 volts across the key contacts.  This would not be good for my little 2n3904 transistor interface.

I also use my set of vibroplex paddles to work with my more modern rigs.  They plug straight into my TS-480, and I built a Norcal Keyer to interface with my older TS-430.  But again, the key jack for my older tube type rigs is not compatible with this keyer.

The answer to all of this is the Jackson Harbor Press KeyallHV kit.  I built it this week, and it works great for all of these situations.

The kit is simple, consisting of an opto-isolator, a capacitor, two resistors, a circuit board and two mosfet transistors. I had to supply a case, input and output connectors, a battery holder and batteries.


Kit components

Construction started with placing major components in place in the box, to make certain that they would fit and function where they would be mounted.


Trial fit

Next, because I chose to make the output totally isolated from ground, I made an insulator from a piece of fiberglass PC board.  I used a grinder and wire wheel to remove the foil from both sides, leaving just the middle fiberglass to act as a mounting plate for the output RCA jack.


Insulator board

Next, I drilled a 1/4″ hole in the insulator board, pretty much centered.  Then I used this hole to mark the location for a larger hole in the metal case that it would be mounted to.  I used a step drill to drill the case hole to a size large enough so that the RCA jack would not touch the case once it was mounted.

Then, I used a small bit to drill two small mounting holes for the insulator plate to the Hammond cast aluminum case.  Using two rivets, I mounted the insulator with the RCA jack installed to the end of the case.


Transmitter interface jack

Once the output jack installation was complete, I mounted a mono 1/8″ audio jack on the other side to act as the input connector for a key or keyer.


Keyer input jack

I used the circuit board from the kit to mark the location of the mounting holes in the bottom of the case.  The two holes were drilled and tapped for 4-40 screws. Then I populated the board with all of the components and wire leads for the power and two jacks.  The completed board was mounted with two 4-40 screws, using two sets of 3 #6 nuts underneath the board as spacers to raise the board up away from the metal chassis.  I didn’t want to short the high voltage lines to ground.

After mounting the board, I wired the input and output jacks, and then mounted the battery holder, using a single 4-40 screw into a hole drilled and tapped into the bottom of the case.  After wiring the battery holder, the electrical construction was complete.

Kit assembled

I tested the kit with my computer interface, as I was curious whether it would work for the most challenging interface.  I hooked my VOM up to the output jack in continuity test mode, then I had the computer send a message through the input jack.  The multimeter beeped a crude code out, not keeping the right timing, because of the way the continuity test works, but good enough to tell that it worked.

Next, I dug out my Heathkit HW-16 from storage.  I had restored it a couple of years ago, then used it for about a year before putting it up in storage. On plugging it in and powering up, I found that the transmitter and sidetone was very intermittent.  So I pulled the covers off and used some deoxit on the bandswitch contacts, as they looked pretty tarnished again.  Funny what a year in a sealed cardboard box will do to a piece of electronic equipment.  Anyway, that fixed the problem, so I moved on to building interface cables for the rig.


Interface cables

First, I made an RCA plug to 1/4″ plug to go from the KeyallHV to the HW-16.  Next I plugged the straight key into the KeyallHV and the 1/4″ plug into the HW-16.  Keying with the straight key worked fine.

Next, I made a 1/8″ mono to 1/8″ mono cable to go between the Norcal Keyer and the KeyallHV boxes.  Then, plugging the Vibroplex paddles into the Norcal Keyer, I was able to key the HW-16 through the KeyallHV.  Success!

I printed a copy of the schematic of the interface, scaled to fit the cover of the KeyallHV.  I taped this to the cover and screwed the lid down. After relocating everything to my operating position, I am now ready for Straight Key Night tomorrow, and other vintage CW operating after that.


Lid of project box

Theory of Operation

The optoisolator sees the key presses from whatever key or keyer you have plugged into the input.  It then drives the two mosfet high-voltage transistors into conduction to simulate a key contact on the rig side.  Because the mosfets are high-voltage capable, they can withstand the high voltage in the vintage rig’s key jack.

I built the circuit with both contacts at the output isolated from ground.  This will allow it to work in virtually any key configuration.

It is currently hooked up to my HW-16 at my operating position.  My first contact was with K3IAN, Jim, in Los Lunas NM.  Everything worked fine with the straight key, so I’ll do the next contact with the computer interface.


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