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P2222A to 2N3866 on TT2

 

Just upgrading the transistor Q2 from the stock PN2222A to 2N3866 (metal) with the heatsink borrowed from my Super Tuna Kit has yielded an increase in output power from 275mw to 355mw, relatively speaking, without touching the 56-ohm emitter bias resistor. There is slightly more gain in the upgraded part number. We were cautioned in the Buildathon not to reduce the 56-ohm resistor to zero without close monitoring of the temperature of the transistor. I bought a whole variety assortment of trim pots and have clipped off one leg to install it in place of the stock R7. It measures a minimum of 2.2 ohms to ~113 ohms, so it should yield good results in obtaining that near 700mw goal. I do have a couple of versions of the Tuna Topper, so controlling the input power to the final amp would make it a useful feature.

Davey - KU9L
 

I changed R7 of 56 ohm to a fixed 2-ohm metal-film resistor instead of the trim-pot. I am using the 49.6-ohm dummy load from the Tuna Helper. I used two Fluke series 73, a Lowe's electrician special VOM, and a Harbor Freight real cheapie VOM to compare readings.

- The original configuration with the 56-ohm resistor and the Q2?PN2222A transistor yielded ~275mw.

- With the PN2222A uptraded to the 2N3866, I measured ~355mw.

- With the 56-ohm R7 up traded to the 2.0-Ohm metal-film resistor, I measured 8.81 Volts across the dummy load Peak-n-hold circuit initially, and after a 5-minute QSO with my dummy load, I measured 8.55 volts, All four meters were measuring withing 50mv of each other, the above is the average of all four.

Initially: 8.81 Volts Peak RMS x 0.707 = 6.23 volts.
6.23 + 0.3 volts (diode drop of peak-n-hold circuit) = 6.53
(6.53)^2/49.6 (Dummy Load resistance) = 860mw (Initial cold power output).

After a 5-minute QSO warmup:
8.55 x 0.707 = 6.04 volts
6.04 + 0.3 = 6.34 volts (Including diode)
(6.34)^2/49.6 = 810 mw

This is not bad for the baby brother of the Super Tuna. For those who do not think that 810mw is much power, in 1987-1988 I worked all 50 States with my Heathkit HW-9's Power Turned down to 1-Watt Output. The secret was good coax and a 40M rotatable Dipole mounted at 50 ft high and also a 3 ele Yagi on 15M mounted at 50 ft. Both were borrowed antennas and I started with 40M and after getting about 36 states from N. IL, I switched up to 15M for about 9 months. This included collecting all of the QSL cards and verifying that they were all correct. I did this operating casually before work, after work, weekends, and Holidays when I wasn't working overtime, attending holiday meals, doing the garden, mowing the lawn, doing Honey-Do chares, or operating 6M/2M/70CM/1296 CW/SSB Terrestrial & Hamsats which was my main love for about 6 years.

I have another 40th Anniversary TT2, Plus a Beaconator ][?on the way as I want to be set up for 40M, 30M, and 20M POTA. I plan to get the Beaconator setup for 17M and 10M with band modules in addition to 20M. I do operate with my Full Gallon 5-watt rigs and even my 100-watt Icom IC-718 for POTA (Even SSB 5% of the time), but hey, now that my wife and I are on SSA it is time for a little more fun ...

If anyone sees a Patented QRPme misteak in my math from above, I get it, I was the rare right-brained engineer and technician during my aerospace career ... LOL.

Now to schedule a POTA outing to K-6298 at Crooked Lake Wildlife& Environmental Area in the next week or so. My issue is that 40M is less effective by the time I get the wife up, get her medication, make her breakfast, get her dressed for outdoors, & stuff her into the truck. Such is the For Better or Worse Clause & what we do for True Love. ;-) 30M and 20M would be better choices during the here and now for mid-day POTA Activations. I will try to get the video camera to record a portion of the Activations.

Cheers,

Davey - KU9L

On Thursday, February 8, 2024 at 06:37:14 PM EST, David Knapp via groups.io <renewables@...> wrote:


Just upgrading the transistor Q2 from the stock PN2222A to 2N3866 (metal) with the heatsink borrowed from my Super Tuna Kit has yielded an increase in output power from 275mw to 355mw, relatively speaking, without touching the 56-ohm emitter bias resistor. There is slightly more gain in the upgraded part number. We were cautioned in the Buildathon not to reduce the 56-ohm resistor to zero without close monitoring of the temperature of the transistor. I bought a whole variety assortment of trim pots and have clipped off one leg to install it in place of the stock R7. It measures a minimum of 2.2 ohms to ~113 ohms, so it should yield good results in obtaining that near 700mw goal. I do have a couple of versions of the Tuna Topper, so controlling the input power to the final amp would make it a useful feature.

Davey - KU9L

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