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Monday, April 18, 2016

3S4 x 2 Transmitter and 1T4 / 3V4 Regen

I've gotten off to a slow start with my mid 50s QRP-in-the-Park Twins. So far only W3BBO in Erie PA has gotten one of my special QSL cards. Now, though, I'm back from a two week trip and ready to get on the air again.

Thursday, March 24, 2016

3S4 x 2 Transmitter (On the Air)


I've finished my mid 50s QRP-in-the-Park Twins. Today I put them together and got on the air....unfortunately no responses to my CQs, but my 1 watt signal was getting out.

The Reverse Beacon Network gave me hits as far west as Utah, south into Texas and east to Massachusetts, not real strong but I was copy-able. I'll try again tomorrow.

Tuesday, March 22, 2016

3S4 x 2 Transmitter (Wired)

I've finished wiring my new transmitter. To help debug a little I did use three colors of wire; black for the ground and cathode circuits, green for the signal grid and red for the plate and screen circuits. Recommended in the 50s was solid (not stranded) wire and square corners with wires running parallel to the chassis sides. The wiring certainly came out looking better than some of my other projects but lead lengths may be a problem if I try this at higher frequencies.

This transmitter sounds fine and per spec it loads up to about a watt out on 40. I'll need to add more capacity for the pi network to work well on 80.

Fortunately I still have my winter vertical up and tomorrow's forecast is for 8"-12" of snow here in SE Minnesota. I'll have time to be on 40 trying out my 3S4 x 2 - 1T4 / 3V4 Regen station.

Friday, March 18, 2016

3S4 x 2 Transmitter (Ready to Wire)

The paint is dry and it looks good. The parts all mounted with no problems. Wiring is next.

Looking at the actual underside vs my drawings it looks a lot tighter than I had imagined...but, fortunately, only half a dozen or so components need to be wired in under the chassis. Most of the wiring is just that, wiring.

Tuesday, March 15, 2016

3S4 x 2 Transmitter (Waiting for Paint to Dry)

Watching paint dry is never fun, especially since this project needs 2 days for the aluminum primer to dry followed by at least a couple of days for the top coat to dry.

I spending this time looking at under-the-chassis wiring and small component placement. With the addition of a solder strip everything is still looking good. One thing this exercise did help me realize, though, is the amount filament related wiring. I'll probably do the filament wiring first and route those wires closest to the chassis.

Friday, March 11, 2016

3S4 x 2 Transmitter (Metalwork Done)

A major checkpoint is to be done drilling and punching holes in a nice (unattainable these days) chassis.
I also try to mount the major parts to confirm I don't have any surprises or problems.

Next is to clean up a few burrs and then prime and paint the chassis to match my regen.

Wednesday, March 9, 2016

3S4 x 2 Transmitter (The Plan)

After building a 1T4/3V4 regen receiver to go with my 3S4 QRP Midget I decided that I needed to rebuild the Midget. What I'm ending up with is more like a Midget on steroids. It still uses two 3S4s in parallel and runs on 90 VDC but it now fits better with the 1T4/3V4 regen. With matching knobs and paint the two will be my mid 50s QRP-in-the-Park Twins.

I'm making several changes from the original QRP Midget. Since I wanted to run this transmitter and my regen from the same power supply I'm rewiring the filaments for 1.5 VDC rather than 6 VDC. Next, the QRP Midget directly heated 3S4 cathodes require a floating filament supply in order to be keyed. I couldn't share the filament supply between the regen and the transmitter. My fix is to key the 90 V B+ line. I have a WWII key with totally enclosed contacts so I won't find myself across 90V to ground sometime. Next I added an antenna loading control. Given the parts I had and the mid 50s sort of design a pi network made the most sense. Dip and load pi network tuning works best with a plate current meter so I also added that. Finally, I saw no need for the QRP Midget DPDT power switch. I left it out completely. I'll just disconnect the filament supply instead. The original QRP Midget fit in a small Bud minibox. Mine will require a 4x6 chassis.


I've found all of the parts and
laid out the chassis. Next step is to drill...I'm committed then.
 


Saturday, February 27, 2016

2016 Novice Rig Roundup Wrapup

The 2016 Novice Rig Roundup ended last night.
It was neat to hear rigs on the air that I haven't heard in a long time. The NRR also gave me a reason to put my own tube gear on the air. Too often it is easier to sit down, flip on the KX3 and have a QSO. During the NRR, faced with 20 knobs and two meters spread between the 75A4 and Eico 720, I couldn't help but feel master of my universe. There was always one knob more that can be tweaked.

Next year I'll be certain to also have my NC303 / Ranger II combo on the air and, maybe, my Drake B Line.

Wednesday, February 24, 2016

Novice Rig Roundup

I got my novice ticket in 1966 so this year marks, for me, 50 years of ham radio. Back then I had an Eico 720 and a military surplus BC342. 

Last night and today I've been able to participate in the Novice Rig Roundup. This is a week long chance to use and hear vintage novice rigs on the air. It runs for another two days.

For this year's NRR I'm running an Eico 720 at 60 watts and a 75A4. My winter vertical loads up fine on 80, 40 and 15 so I'm having a great time.


Thursday, February 11, 2016

TNT (and Hartley) Notes

Recently I pulled two early draft papers out of my files that, I believe, were written by W2SN in the early 80s.  One was "The Saga of the TNT Transmitter" and the other was "Additional Notes on Self-Excited Oscillators". I posted these at  https://www.prismnet.com/~nielw/W2SNPapers/Saga_of_the_TNT_Transmitter.pdf  and  https://www.prismnet.com/~nielw/W2SNPapers/Additional_Notes_Self_Excited_Oscillators.pdf   .

The 1986 Callbook lists W2SN as Vernon Clifford, Amityville, NY. He got into ham radio in the early 30s using a TNT transmitter. Almost 50 years later he decided to build an exact replica of his first rig. Finished, it looked good but when he put it on the air he got a T7 report with a bad chirp. In these two papers he details what he tried (and learned) as he attempted to clean up his signal.

Most of us have had a much better experience with the TNT transmitter than W2SN but I've heard some pretty crummy signals also. There is no doubt that the TNT circuit can misbehave with no one "silver bullet" fix but W2SN tried a lot of fixes and nothing seemed to work.  My TNT transmitter certainly sounds better on 80 than on 40. Perhaps most of W2SN's testing was on 40 or, heaven forbid, 20. He also never showed the layout of his transmitter. Perhaps there was a basic problem there.

W2SN does make several points beyond the typical TNT transmitter construction/setup instructions to look at including:
  • Try DC versus AC on the filaments
  • If AC filaments, check that the center tap resistor is centered
  • Bypass and/or choke the power and keying leads to minimize stray pickup
  • Don't use a wood (or wood filler) grid coil form
  • Insure a well filtered and stiff B+ supply
  • Tune the antenna network to minimize RF in the shack 
  •  Insure a good station ground to minimize RF in the shack
 W2SN also identified these potential issues. Comments?
  • The value of the grid leak
  • The value of the filament bypass capacitors
  • Bad feedback stability due to changing tube grid-plate capacitance
W2SN's final solution was to use a Hartley. In his case he needed to take this drastic measure. This solution does not necessarily apply to all of us.

My TNT transmitter shows some (if not all) of the same problems that W2SN saw on 40 mtrs but sounds fine on 80. Next fall I'll look at some of the areas that W2SN mentioned to see if I can get a better signal on 40.

( Have you seen a polished version of these articles? If so, please let me know.)