Restoring a Damaged HX1681 CW  Transmitter and Building a Scratch Built HP-23 power supply

Restoring a damaged and questionable operational state of a Heathkit HX1681 transmitter and building from scratch an HP-23 power supply to power the transmitter.

The pictures show the condition of the transmitter when I purchased it on eBay. The bottom half of the cabinet was missing, replaced with a piece of sheet metal bent to fit.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The rear panel is in excellent conditions. An 11 pin female socket was included, saves on having to find one later on. The lower left corner of the rear panel is bent.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Missing are the VFO and final amplifier top covers. The TUNE control dial cord needs replacing. The VFO dial during tuning was hanging up a third of the way through its rotation. The problem was caused by the VFO dial “Clutch” friction was too little. Tightened up the clutch screws fixed that problem.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I found a bottom cabinet cover and both VFO and final amplifier top covers. A ham friend had them so that solved that problem. The bottom cover had some damage on the right front corner. Notice the “White” area in the picture below between the top and bottom halves. The corner was bent quite a bit. I used a small “tack” hammer and a vice to straighten the corner as best as I could. It’s not perfect but it looks rather good. It all will look much better once I sand and paint both halves of the cabinet.

 

 

 

 

 

 

 

 

 

 

Right side front view. Looking much better.

 

 

 

 

 

 

 

 

 

 

Rear view showing the 11 pin female plug  and 11 pin male connector. There is a slight bend in the lower left corner of the rear panel, next to the paste on label. It appears the transmitter was dropped. I was able to bend the lower left corner of the rear panel back into shape.

 

 

 

 

 

 

 

 

 

 

 

HP-23 Power Supply Scratch Build

I re-stuffed four 125ufd 450VDC 85c filter capacitors I picked up on eBay with all new 150ufd 500VDC 105c capacitors.

 

 

 

 

 

 

 

 

 

 

 

New capacitors mounted on the original capacitor base and ready to be sealed up and put to use. I used J.B. Weld to seal the can tops to the bases then slide the original Black cardboard covers back over the capacitor cans.

 

 

 

 

 

 

 

 

 

 

 

9/8/2019 Scratch Built HP-23A Supply Complete

Scratch Built HP-23A is complete. All new point to point wiring, new axial lead capacitors, new 150ufd 500VDC 105c snap in capacitors stuffed into the original can caps, upgraded the 20ufd 150VDC caps to 22ufd at 250VDC caps. Installed small DPDT toggle switch wired as a SPDT switch to select 250VDC LV or 350VDC LV at pin 3 on the power connector. Fuse holder with a 4 amp fuse replaces the original HP-23A circuit breaker. New wiring is tied up with zip ties, making the wiring a lot cleaner. Power cord is a new 2 blade Polarized cord with AC Hot wired through the fuse holder and radio’s ON/OFF switch pin 9 to pin 10.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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HX1681 HET OSC/MIXER Board Problems

  Update

8/13/2019

The HET OSC/MIXER boards shown below have problems on 10 meters, no RF output. One board came from a questionable HX1681 I purchased on eBay and the other board came from a ham friend as a spare.

I performed work on both HET OSC/MIXER boards shown below. The top board had no RF output at the RF OUT socket on 80 and 10 meters. I traced the 80 meter problem to a broken Toroid transformer lead. The lead was broken too close to the winding so I rewound the transformer (28 turns) with new magnetic wire. This fixed the loss of 80 meter RF output.

The bottom board also loss output on 80 and 40 meters. I traced the 80 and 40 meter problem to a failed 500 ohm pot that had opened.  New pots that are the same as the original are very difficult if not impossible to find. New pots are much smaller and the pin orientation is quite different. The original pot was replaced and the board now has RF output on 80 and 40 meters. The 500 ohm pot is in series with Q101’s Emitter to Ground. An open pot will cause Q101 (80 and 40 meter crystal oscillator transistor) to cease oscillating hence resulting in loss of 80 and 40 meter output.

I continued work on both boards to fix the loss of 10 meter RF output at the RF OUT socket. I traced the problem on both boards to the 10 meter Band Pass Filter’s C162 and C163 trimmer capacitors. I ordered new 2-8pf ceramic trimmer capacitors to replace the original plastic 2-8pfd trimmer capacitors. Once installed and adjusted, both boards have 10 meter RF output at the RF OUT socket. The small square components to the right of both boards are the original plastic trimmer caps. They are known to become intermittent or simply outright fail. To eliminate the possibility of future failures of these flaky trimmer caps I simply replaced them with new trimmer caps. Both boards now have RF output on ALL bands, 80, 40, 20, 15 and 10 meters.

I have one more board in a second HX1681 transmitter that has similar problems on 10 meters. I’ll be working to restore 10 meters on that board as well.

 

 

 

 

 

HX1681 10 meter fixed