New KX3 QSL Card

It's a new "QRP in the Park" season and I have a new rig. I need a new QSL card.

My new card, using Walmart digital photo printing and 3.3"x4" Avery shipping labels, costs about $.30 each in single quantities. This is a great match for my operating style. Rarely do I get on the air and work 100s (or even 10s) of hams in a short time. It would take me forever to work through 100 or more pre-printed QSL cards. This way I can make up QSL cards 5-10 at a time and easily update them without throwing out a bunch of unused cards.

Interested in doing the same? See my January 2, 2010 blog entry.

KX3 in Silver Lake Park

Today the weather finally turned warm, sunny and dry. It was also Mother's Day, a good reason to avoid the restaurants for a picnic in the park. I did get a chance, though, before the picnic to practice my favorite operating pastime. I found several signals on 20 mtr CW. Gary, K5ON, answered my CQ. We had a great QSO. The KX3 again performed great....love that roofing filter.

Packing my Elecraft KX3 for a trip

I'm getting ready for summer trips and outings with my Elecraft KX3. I found a the right size padded bag at Goodwill for $3.00. See my video at  KX3PicnicTableQRPPack

Elecraft KX3 is here!

Today I was at the Rochester, MN UPS depot at 10AM sharp to pick up my new radio. I got serial number 43 of, I expect, thousands. Elecraft has crammed a lot into a small box. I spent most of the day figuring out how to use it.

One QSO so far. KB5AE in Ada, OK answered my CQ on 20 CW. He reported a fine 579 signal down his way.

TZ-20 Amp Output Circuit

This morning I was showing off photos of my TZ-20 amplifier when one of my friends commented that it certainly was wireless, just look at the one rotatory switch with no wires attached to it. This reminded me that I had one last update to post on this project.

After WWII almost every transmitter project (except the simplest starter sets) had a pi network output stage. This was not as common in the 30s. Most transmitters then had link coupled output followed be some sort of antenna matching network. Many times the matching "network" was a variable capacitor either in series or parallel with the output link. A series capacitor worked best for low impedance loads while a parallel capacitor was used to feed into high impedance loads. Today's norm is a 50 ohm antenna antenna/coax system requiring a series capacitor.

SW3, a rotatory switch, controls course loading. C5 is the fine loading adjustment. With SW3 I can switch out the series capacitor all together or add in additional capacitance to give me a total range from about 20pF to 900pF. Tune up becomes very much like a pi network "dip and load". With SW3 and C5 set for minimum capacitance the plate current is dipped using C4. After dipping, the loading capacitance is increased using C5, C6 and C7 into the range of operating plate current and then the current redipped using C4. C4, C5, C6 and C7 interact so this process must be repeated until the last C4 adjustment puts the plate current where it needs to be for full output...in my case about 150 mA. 500 VDC on the TZ-20 plates at 150 mA gives me 75 watts input.

AWA 2012 Linc Cundall OT CW Contest

This afternoon I wrapped up my participation in this year's Linc Cundall OT CW Contest. Obviously I'm not a major contester. During the 48 hour contest I netted nine contacts. Not many contacts/points but I did enjoy putting my latest homebrew transmitter on the air.

This year I used my new "Taylor 75", a 1934 style oscillator-buffer deck driving two Taylor TZ-20s in push-pull. The receiver was a National NC-101X. Everyone that commented indicated that the transmitter sounded fine. Keying the buffer stage helped. With the crystal oscillator running continuously (on transmit) there was no sign of chirp.

I went ahead and created a QSL card to send out.

On the Air

Today I got on both 80 and 40 using my new 75 watt transmitter. This afternoon I had a nice QSO on 40 with KC9RXI, Tom, in West Salem, WI and this evening on 80 with NS7E, Art, in New Prague, MN. Both Art and Tom reported no problem with my signal.

Tremendous!

It Works!

After a couple of days scratching my head and asking around trying to figure out why my TZ-20 amplifier wasn't working up to expectations I finally did what I should have done first. I checked the wiring.

One TZ-20 wasn't connected to the final tank coil. I was running with only half an amplifier and a poorly designed one at that. It worked but not well. Once I fixed the wiring error power levels jumped to the 50-60 watt range. Neat, but now I needed to deal with typical amplifier problems.

TPTG feedback -The first problem I had was that the amplifier took off on it's own (without any drive) when the input/grid circuit was peaked for maximum output. This was solved by removing C3, the TZ-20 grid tuning capacitor, from the circuit. C3 in the amplifier and C8 in the final tank circuit of my 1934 transmitter interacted anyway so this eliminated one pesky control. Problem solved but now the drive level was way down...one solution led to another problem.

Drive level - With no tuned circuit on the grids of my TZ-20s they were not getting the drive needed to get anywhere close to full output. This one was solved with a new coil for L1/L2. More turns for L2 got the power transfer up to the point that now I'm easily driving the amplifier to 75 watts input.

Bias - This all started with me wondering if I has the bias set right. The advantage of the TZ-20s is that they do not need an external bias supply to protect them when the drive goes away. With no drive (and no bias) plate current drops to almost zero. For the TZ-20 a simple resistor from the grid to ground is all that's needed to produce needed bias....but what value? It turns out that the 1939 Taylor tube manual has a formula for calculating recommended Class C CW grid bias for a given plate voltage, in my case 500V. Bias came out approximately 20 volts. I'm driving the grids to about 30mA ... 20V/30mA = 666 ohms. I had a 750 ohm resistor, close enough.

One question that had to be dealt with was how best to couple the output to the antenna. It turns out that, for my 40 turn tank coil, a four turn link gives me maximum output into my 50 ohm dummy load. I am set up, though, so that I can add a loading capacitor in series with the link to cover real world antenna conditions.

Now I have an amplifier for my 1934 transmitter that takes about 6 watts of drive to run 75 watts input (45-50 watts output) on 80. With a couple of new coils I should be able to put it on 40.

Look for me during the AWA Linc Cundall OT CW contest next week.

TZ-20 Operating Specs?

I've gotten my TZ-20 RF amp up and running with my three tube 1934 transmitter but its not working like I expected.

I'm running with 500V on the push-pull plates with the recommended 2K bias resistor. Key down I'm seeing grid current (total for the two tubes) of about 40mA and total plate current of 40-50mA. Looking at the TZ-20 specs and tubes curves from the 1939 Taylor Tube manual I expected to see 50-75 watts input with 35-50 watts output, instead I'm seeing 20-25 watts input and only 8-10 watts output. I do have three TZ-20s. Any two of them behave the same. What an I doing wrong...or is it working as designed?

Elecraft KX3 On Order

It's winter here and I'm already thinking about spring!

After 10 years I'm retiring my faithful K1 for a brand new Elecraft KX3. See http://www.elecraft.com/KX3/kx3.htm for the details.

I'm excited. The KX3 It covers all amateur bands, 160-6 meters, operates phone, data and CW, and it is software defined and DSP-based. It will allow me to do digital/PSK31 from the picnic table without an attached computer and the the receiver looks like it should be great.
The first thing on my list was the ATU. With it I should be able to easily load into my favorite end fed half wave antenna. Next was the roofing filter. QRM can always pop up. I ordered the KX3 assembled to make certain everything was aligned right and that it worked straight out of the box. Why the mic? The rig supports CW, phone and data. This will allow me to try a little QRP phone operating, especially if demoing the rig.

Unfortunately the estimated ship date is almost two months away. I'll have to wait.