Knight-Kit T-60 Becomes a KPD T-160

Adding 160 Meters and Plate Modulation to an Early Novice Rig

This project is dedicated to K1DC Don Benecchi. Don is a true friend, elmer and finer sailor who graciously donated the Mod transformer that made it all possible. Thanks DON!

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The Knight Kit T-60 was a common beginners transmitter in the late 1960s. It was designed to provide AM and CW on 80-6 meters. It has about 60 watts of plate input on CW and an unnamed amount of screen grid modulated AM. To keep costs down it used a common TV sweep tube in the PA. It offered to the eager novice the upgrade potential to AM and 6 meters as the higher ticket was obtained and could be bought with a summers worth of lawn mowing savings.

Economically built ,they were the Rodney Dangerfield of rigs from that era. In addition they seemed capable of transmission on many frequencies at once. The only FCC notice I ever received was with a spur from my T-60 back in 1969.

However, I have always had a soft spot for them and picked a well used one at a local ham fest. Now what if they could also run on 160 and were plate modulated?

Playing around with the circuit I saw no reason why t would not run on 160. All I needed was the correct Osc. and PA values.

Since I did not plan to use the rig on 6 meters, I moved all oscillator coils over one lug on the bands witch and added a coil/cap combo to the former 80 meter spot. Rotating the switch a few degrees and it stopped at an empty panel spot just below 80.meters. I only care about 160, 80 and 40 so I rewound the PA coil with close windings and taps for those bands.

Plate modulation was a bit more trial and error. I decided it would be fun to modulate the 6DQ6 PA with another 6DQ6.

There is some information on the 6DQ6 as a Class C PA and none as Class A modulator. However I became comfortable that I could run the tube at about 20 watts input and run a second one as a single ended modulator. There is some information on the web that lead me to at least try it. Admittedly the power supply would probably be groaning a bit




Standard T- 60

The 6DR7 screen modulator is located between the RF choke and the large 6DQ6 PA

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T -160

Note that the filter capacitor has been moved to under the chassis, the PA coil has been relocated, the K1DC Stancor modulation transformer has been installed (upper right corner), the 6DR7 has been replaced with a second 6DQ6. In addition a small cap is located between the tuning and loading capacitors. It is switched into the plate cap when in use on 160 meters.




Standard T- 60



T -160

I added an extra wafer to the band switch to add in the extra plate tuning capacitance needed for 160. The Osc coil for 160 is the tan object located to the left of the band switch.

Note the replacement of the 9 pin miniature socket with the larger octal for the 6DQ6.

Conclusion

It works! It took a lot of tinkering and playing around but on the air tests on 160 shows that it will play. Audio looks pretty good on the scope too. Power supply transformer seems to be holding up though it does get noticeably warm to the touch.

A few clean up items. I was getting a bit of a cherry glow on the modulator. I increased the cathode resistor and that went away with a slight loss of audio. Not enough to harm the next QSO I had.

Next step was to increase the screen resistor on the PA a bit. I wanted to limit the plate current to 50 MA since that is the max rating on the mod metal. I am now getting 414 volts on the PA with 54 MA of current. which gives me just about 22 watts of throbbing PA power. And the modulator seems real happy with that combination

Its no Collins rig, but I learned a lot getting it this far.

Oh, and I had to change the model number.....




To see the companion Hallicrafters S-38 that has been souped up, go to the Souper 38 Page


Go back to The WA1KPD  Radio & Boatanchor Page

Last updated09/01/08