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HW-16 Transmitter Work

 

HW-16 Transmitter Work

Now that the receiver seemed to be working great, it was time to work on the transmitter some. The first thing I noticed is that the meter was indicating about a third scale with no power applied. I had read of another ham with this problem, who found that the meter had become magnetized. Convinced that I had the same problem, I spent about 15 minutes trying to degause the thing using an assortment of homebrew degausers. But none if it worked. Then, as I was moving the meter around in my hand, I noticed that there was a mechanical zero adjustment hidden underneath the meter movement.

 
Meter mechanical zero adjustment

I didn’t think that it would have enough adjustment to fix the problem, but that is what it turned out to be. A simple adjustment, and the meter was back to zero.

 
Meter correctly zeroed

I had ordered three crystals from Bry Carling, AF4K (www.af4k.com). They arrived promptly, and now I was ready to check the transmitter out. I ran through the basic transmitter checks in the manual. At first, I had no power out at all. I traced that to a broken wire on the power adjustment pot. Once that was restored, I had power out into a dummy load, at reasonable levels on all three bands.

Next, I followed the transmitter alignment procedure for the transmitter section, including the neutralization of the final. Instead of relying on the meter to adjust for minimum power in the test, I hooked my o-scope up to the antenna connection with the 50 ohm dummy load hooked up as well. Then I adjusted the neutralizing cap for minimum waveform on the scope. After hooking everything back up for normal operation, I still had reasonable power out on all three bands, with 15 meters being just a bit lower than the other two bands (30 watts vs 50 watts).

So now everything was basically working as I think most HW-16s have always worked. Somewhere around 45 – 50 watts out on 80 and 40 meters, and somewhere around 35 watts out on 15 meters.

I had read of one modification that I wanted to try, as the fellow who wrote it up claimed that he got 50 watts out on 15 meters with the mod in place. He claimed that the problem was that the final tank circuit had a bit too much inductance to be efficient on 15 meters. The mod was to spread the bottom windings (for 15 meters) of the output tank coil out to slightly reduce the inductance.

Before the mod, with the power control fully CCW (minimum power), I had about 31 watts out on 15 meters, 47 watts on 40 meters, and 51 watts on 80 meters.

 
15 Meters output minimum power before mod

After removing the coil, I noticed that the connection on the bottom of the coil (common to all three bands) was loose and had a cold solder joint.

 
Cold solder joint

The 15 meter section of the coil is close wound on the form.

 
Normal spacing of turns

I used my AADE Capacitance/Inductance meter to measure the inductance at each tap before the mod was applied.

15 meters: 1.321 uh

40 meters: 4.214 uh

80 meters: 7.589 uh

 
15 meter inductance read before mod

I spread the turns out in the 15 meter portion of the coil as best I could, while avoiding touching the steel mounting screw at the bottom. It didn’t allow for much spreading, but I got some.

 
Coil with turns on bottom spread out some.

Once that was done, I sealed the windings in place with some of the XYL’s clear fingernail polish.

 
Sealing the coil windings in place.

After the mod, I had the following inductance readings:

15 meters: 1.182 uh

40 meters: 3.938 uh

80 meters: 7.288 uh

 
15 meter inductance after mod

After installing the coil form back into place, 15 meters was improved very slightly ( went from 31 watts to 35 watts out in the lowest power setting (about 125 ma at plate current dip).

With the highest power setting (about 180 ma plate current at dip), I got the following reads on each band:

80 meters: 60 watts

 
80 meters full output
 
 

40 meters: 57 watts

40 Meters Full Output

 15 meters: 38 watts

15 Meters Full Output
 

Receive is still good at this point, so I think I will call it good for now. I can’t think of any mods that I want to do further to this nice old rig.

Migrated Comments:

3 Responses to “HW-16 Transmitter Work”

  1. Bob Says:

    Thanks for posting this. I just got an hw-16 off ebay and someone rewound the coil (badly) and I was trying to figure out what the original values were. The close up pictures and the inductance readings are very helpful !

  2. Michael Miller Says:

    Thank you. Very well done. I have two HW-16 with HG 10 B vfo’s.
    By the by, photo’s are excellent quality.

    73 de Mike W9MVM

  3. LarryC Says:

    Hi there. I bought the replacement electrolytics from Hayseed and new pwr resistors. I bought new HV diodes from eBay since the rig I hv is dated from 1968. THe tank circuit mod is accomplished by moving the 15 meter tap LOWER by one turn. SUpposedly that raised the output on 15m to 50 Watts. The weblink for that mod no longer works but I wanted to share it here. THanks.

    Larry, N3CCW (Everett, WA)


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