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Thursday, December 20, 2007

BA on 20mtrs

Tuesday I got on 14.050 cw using one of my boat anchor stations. The station of choice this time was my Collins 75A3 and Central Electronics 20A. In the mid 50s the 20A was one of the first commercially available SSB exciters but it also works fine on CW running about 20 watts. I use mine crystal controlled. Contacts on Dec 18 in the early afternoon included both W5ZR (LA) and NV4I (SC).

Wednesday, December 19, 2007

AWA 1929 CW Party

With snow on the picnic tables here in Minnesota my operating has moved from K1/QRP to the boat anchors in the basement. The AWA 1929 CW Party occurred the first two weekends of December. This contest requires that the transmitters reflect 1929 or older technology and tubes. Participation is in the 50 - 100 station range so it is a fairly low key "contest". Even the required log information forces operators to slow down as name, QTH, signal report and transmitter descriptions are exchanged. Power is limited to 10 watts input (except for late east-west QSOs) on 80 and 40 meters. Many of the transmitters are self excited Hartley, TNT or TPTG oscillators link coupled to the antenna. Some are MOPA (master oscillator-power amplifier) two stage transmitters. I put my TNT transmitter on the air with my National NC-81X receiver. Running about 2 watts out on 3560 KHz I had seven enjoyable QSOs. Longest "DX" was N4GJV in Cleveland, NC. All of the others were in MN and WI. The contest was not without some last minute challenges, but not with the 1929 gear. As I got started I realized that I had no way to zero beat my signal. The '81X muting function has no mute bypass switch. With it wired into my T-R relay to mute on transmit I had no way to tune my receiver to listen for my own frequency. Fortunately the '81X is ham band only with relatively good calibration so I wasn't to far off ... but then the NC-81X receiver dial string broke. My receiver could be tuned just fine but I had no direct frequency readout. I made it through the contest by listening for a signal of known frequency and then not straying far from that. It was a fun evening.

Monday, November 26, 2007

More NC-57

I added a Heathkit QF-1 Q-Multiplier ( ) to my NC-57. The QF-1 provides additional selectivity or signal rejection as desired. It was marketed by Heathkit starting around 1956 and was a fairly common accessory. It requires a connection to the IF stage plus B+ and filament voltages available at the NC-57 accessory socket.

I found this to be a big help. The QF-1 effectively eliminated the CW audio image (ie. a readable signal each side of zero beat) common in receivers that don't have a crystal filter. Eliminatling the audio image eliminated half the QRM on the band.

Wednesday, November 21, 2007

NC-57 Project with comments about the NC-125

For the past few days I've been going through my NC-57. This radio was marketed by National in the late 40s and early 50s. Features include a built-in speaker, electrical bandspread (uncalibrated), regulated B+ for the HF oscillator and a tuned RF stage. Advertised frequency coverage was .54-55MHz. See for more information.

My set had been already gone through by a previous owner, recapped and aligned. This set includes an extra dial string in the bandspread tuning assembly to overcome slipping. While this radio generally worked it also would go dead once and a while for no apparent reason. Close inspection revealed a cracked solder connection on a filament pin of the 6H6 detector. Resoldering this connection fixed the problem.

Properly aligned, the calibration was excellent and sensitivity good but this radio is still only one step removed from a simple SWL receiver. Mechanical and electrical stability is marginal, especially above 40 mtrs. It was no surprise that SSB and CW signals easily overloaded the receiver and BFO. Operation with the BFO requires running the AF gain wide open and controlling volume with the RF gain control. I did like the positive feel of the main tuning. While National used a failure prone dial string for bandspread tuning, main tuning uses a gear/pinch wheel mechanism.

Three years after introducing the NC-57 National came out with the NC-125. Under the covers this "new" receiver was simply a NC-57 with the internal speaker replaced by an S-meter and Select-O-Ject audio filter. Both of these features were available as options on the NC-57. National also replaced the round dials with slide rule dials. Unfortunately National took a step backwards by using slip prone dial strings on both the bandspread and main tuning. The Select-O-Ject feature, while unique, does nothing to remove the audio image. I believe a Q-multiplier similar to the Heathkit QF-1 would have been more useful.

I acquired a tilt base with my NC-57. Besides tilting the radio front for easier reading, this also allows a ham to add extra station controls and some accessories without cluttering up the shack. High on my list is a 1MHz crystal calibrator to help set the main tuning for repeatable bandspread calibration over each ham band.

I plan to use my NC-57 on 80 and 40 with one of my early novice transmitters.

Sunday, October 28, 2007

QRP Operating - Austin, TX

On October 26 I finally had a chance to do some more K1/QRP operating. This time while on a trip to Austin, TX. The weather was great: sunny and about 75. My antenna was again a 67' (full wavelength on 20 mtrs) endfed wire . The operating position was on second floor balcony. I ended up running my antenna up to eaves above me and then sloping down to a fence along side the yard. My clear view was to the east and I was on top of a bluff over looking Lake Travis.

A few minutes before noon I had a QSO started with KC9AWL, Len, in Palm Coast, FL on 14.057. He gave me a 559 but when I noted how deep the QSB/fades were I knew we were in trouble. Len turned it over to me but, evidently, the band went south and he lost me. I never heard him a second time.

Within ten minutes I had another QSO going on 14.057, this time with WA9FZP, Phil, in Racine, WI. This enjoyable QSO lasted about 1/2 hour with 559-569 signals the entire time.

Sunday, August 26, 2007

815 Transmitter Postmortem

After weeks of vacation, etc I finally got back to my 815 transmitter. To recap ... the major mods since the original design shown in the ARRL handbook and my blog entry dated March 19, 2007 have been to 1) add a loading capacitor between one side of the output link and ground 2) Replace R4 with an RFC to a 200-300 VDC supply and 3) replace the 815 screen voltage dropping network R5/R6 with an RFC to a 200-300 VDC supply. The final layout is shown in my May 28 blog entry.

Tests on 40 meters have been a little disappointing. The 815 runs at only 35%-40% effeciency into a 50 ohm load. 50 watts input gives only about 20 watts out. (whoops! I checked my Drake watt meter agains a Bird. Turns out that the Drake watt meter is reading way low. The Bird says I'm putting out about 30 watts. This is about the power output I expected.) Also the transmitter is not real forgiving. If misadjusted, it goes into self oscillation or generates a trashy sounding signal.

This one will go to the back of the shelf. (but after discovering the watt meter error, only while it waits for a power supply)

Friday, July 6, 2007

More QRPxpeditions

Over the past week I've enjoyed QRPing from both Milwaukee, WI and White Water State Park in SE Minn aboth times using my K1 feeding a 34' endfed wire on on 14.060. In Milwaukee I worked Butch, KD5RSS, in Haskell, OK and Dick, W0NTA near Loveland, CO. Dick and I were both running 5 watts and we were 599 both ways. His antenna and high QTH makes up for a lot. At White Water State Park near St. Charles, MN I found a point on top of the bluff on the west side of the White Water River valley. Conditions weren't specticular but I did work KB3AAG, Frank, in Delphene, PA and N5GW, Gene in MS.

Tuesday, June 26, 2007

QRP / K1 Video

Here's a video that I just posted on YouTube. In it I demonstate setting up my QRP station, show some of the features of my K1 and then talk a little about my QRP operating experiences. The video itself was done by John Reed K0KTY (SK) about 2 years ago.

Monday, June 25, 2007

QRP Operating

Today I finally made it away for some more QRP operating. This time it was to Great River Bluffs State Park (See ). This park is along the bluffs of southeastern Minnesota overlooking the Mississippi River Valley. From my operating position I could see far into Wisconsin and watch the hawks soaring below me. Using my K1 and a 32' endfed wire on 14.060 I worked both K7UP, John, in Elephant Butte, NM and W2BWQ, Gene, in Congers, NY. Conditions were only fair with QSB a problem. I heard only half a dozen stations across 20 mtrs.

On the 815 transmitter front it needs a better regulated suppy for both the 815 screen and the oscillator plate. The dropping resistors have to go.

Monday, May 28, 2007

A working 815 transmitter

I have a working 815 transmitter. Unfortunately I had to "glue" a capacitor on to the side of the chassis to do it. Key to getting the final to work into a variety of loads is some sort of antenna tuner. Adding a capacitor into the grounded side of the output link does just that. The added capacitor does output loading . Tune up now amounts dipping the final with C2 and increasing/decreasing the loading with the added output link capacitor. Typical operation is 50 watts input and 35 watts out.

Eventually the loading capacitor will be hidden behind a front panel.

Friday, May 25, 2007

QRP (and a little homebrew)

After a couple of days of on and off rain with cool weather here in SE Minnesota, today was sunny and temperature about 70 ... great evening for a picnic and a little QRPing from the park. We chose to go to Florence Park in Stewartville, MN. With my K1 and 67' endfed wire in a tree, 20 mtrs sounded pretty dead. An early CQ did raise K9PWK but QSB was bad and we lost each other before we really had much of a QSO (he gave me a 229). Finally at 6:45 Terry, N4IY, in Borden, IN came back to me. We had a nice QSO. His 4 watts was doing a fine 579 job.

On the homebrew 815 transmitter front I've been trying to get the final coil wound so that the transmitter delivers full output to a 50 ohm load. At this point I'm about to add an outboard antenna tuner to my project list.

Monday, May 7, 2007

I've powered my new transmitter up on 40 meters.

For use during this test phase I built an adapter to allow the use of B&W 5 pin JVL transmitter coils instead of winding coils on my National coil forms. I'm also temporarily connecting the bias and voltage dropping resistor networks to the back 12 terminal barrier strip. This way I can easily play with the resistor values to get the right voltages.

The transmitter loads up to 40 watts input and 30 watts output with no sign of self oscillation

I've still problems, though. The 815 screen current won't come down. It appears to draw around 60 mA rather than 15. High screen current causes the screen dissipation to be exceeded, maybe damaging the 815. Right now I'm looking for another 815 to compare readings with.

Sunday, May 6, 2007

A mid 30's Three Tube Regen

I aquired another radio last week. This one I "won" through ebay. The pictures posted on ebay showed a fairly ughly set with three mis-matched dials. The layout, though, suggested the "Three Tube Regenerative Receiver of Unusual Performance" by George Grammer and written up in the January 1933 issue of QST.

I bid and the gamble paid off. Underneath the flaking paint front panel and cabinet was a fairly nicely done version of George Grammer's design.

George grammer's original article was more than another construction project. He spent a large part of the article talking about features of good regen receiver design before describing "a practical receiver". This receiver includes a tuned RF stage and general coverage/bandspread tuning. Bandspread tuning is via the drum dial at the left after the detector and RF stage bandset capacitors are set. The receiver showed up in the ARRL handbooks through 1937.

Wednesday, April 25, 2007

815 Transmitter Coil/L1

L1 of my transmitter calls for ten turns on a 1" coil form spaced over 7/8". I had the form and the wire I needed. Winding spaced turns, though, takes a trick. I first wound the ten turn coil on the form, tightening the wire as much as possible. The turns were not even. It was not pretty. I then wound another "coil" (the red wire) forcing evenything to space out evenly over the 7/8". This I heavily coated with clear fingernail polish. After the fingernail polish had dryed I removed the red spacer coil and recoated with fingernail polish.

Monday, April 23, 2007

Picnic Table QRPing in Decorah, IA

We spent the weekend in Decorah, IA and on Saturday and Sunday I had some spare time for hamming. I used my K1 with a 67' endfed wire up in the tree above the campsite. With the K1's built-in antenna tuner it loaded up on 40, 30 and 20. Sunday afternoon at 3:00 I did finally did have a QSO with Ken, WA8REI/4. He was on the Appalachian Trail at Newfound Gap, NC near Gatlinburg, TN. We were on 14.060, both running battery/5 watt power into end fed wire antennas. With some amount of QSB, signals were around 579. For the bottom of the sunspot cycle I was pretty happy.

See more examples of my QRP operating at

Monday, April 9, 2007

Final 815 Transmitter Layout

I've finally committed to a layout and mounted the major parts. From left to right along the front is the xtal (with B directly above it) C1 and C2. Left to right on top is 6V6, L2/L3, 815 and L4. RFC2 is mounted upright behind the 815 and L4. I elevated L2/L3 so that it could be mounted directly above C1. The toggle switch on top of the chassis in the right front corner is to short out L1 when not multipling in the tri-tet oscillator. The extra space along the back is reserved for whatever is needed to get the screen and oscillator voltages right. The spotting switch will probably go in the space between C1 and C2 with a cathode current meter mounted directly above it (if I add a front panel).

Saturday, April 7, 2007

Final Layout / Drilling Guide

After "playing checkers" for several days tweaking the layout, I'm ready to drill. I usually mark major component locations and holes using masking tape. After I'm done the tape can be removed leaving no markings on the chassis itself.

Thursday, April 5, 2007

Another Power Supply Option

Bryan, WA7PRC, pointed out to me that an "economy" power supply would be a more elegant way of getting the lower B+ needed for the oscillator stage then wasting power in multiple dropping resistors.

From Bryan:

"It's an easy way to obtain high- and low-B+ voltage sources.  In fact, there's more than one way to skin a cat... center tapped or non-center tapped transformer using a fullwave doubler.  In both cases, the output voltages differ by a factor of 2. The doubler, aside from needing a transformer with only a single secondary winding, has the advantage that the output voltage is 2.828 RMS instead of only 1.414 RMS.  So, your secondary can be 177VRMS instead of 354VRMS. Practically speaking, because of resistance losses, the voltage would be somewhat lower under load.  And of course, you'd still need whatever VA rating, so the transformer size/weight would be the same.

With either topology, you'll have a significantly lower low-B+, and should you decide to use a regulator, will not have to dissipate as much power in the series resistor."

Wednesday, April 4, 2007

815 Transmitter Power Supply

I keep a couple of generic brute force power supplies around to use with my homebrew projects. This one grew out of a much modified and cannibalized WRL transmitter that I found at a swapmeet several years ago. From the back, on the right side is the high voltage section including transformer, choke, filter capacitor and rectifier tube. It will easily deliver the 500 VDC at about 200mA that I need for this project. On the left side is the bias supply. This section has a VR-90 with a pot across it. The exact bias voltage is set and then left alone. The six foot cable shown will plug into an octal socket on the back of the 815 transmitter.

Tuesday, April 3, 2007

QRP Operations from W0IBM shack

Today was a great day to stay inside in SE MN: windy, overcast, temp in the 30s and snow in the forecast.

The first Tuesday of the month is informal meeting day at W0IBM, Rochester, MN. ( see ) I took along my K1 as show and tell. 20 wasn't real active but I hooked up to the W0IBM three element yagi and managed a contact with George, KF4UCC, in Chesapeake, VA.

On the 815 transmitter front I've done a rough layout to help orient tube sockets and studied the dimensions a bit more. It still looks like it will fit. I'm just about ready put the drill to that virgin chassis.

Wednesday, March 28, 2007

815 Xmtr parts

Here's the collection of parts needed to build my transmitter (the power supply is separate). I'll mount the male 8 pin plug on the back of the chassis for power. The barrier strip is for metering points and for the key connection. I'll be able to connect in a plate modulator here also. In the final transmitter the two 25 watt pots will be replaced by wire wound resistors.

Sunday, March 25, 2007

Additional 815 xmtr Mod

Another feature missing from most pre-WWII transmitters is some sort of spotting capability. Two reasons drive the need for spotting capability today. First, with transceivers being the norm, operators rarely tune the band looking for a response to a CQ. If answering a CQ, you need to be close to on frequency. Operating in an open spot on the band is the second reason for a spotting switch. Choosing the right operating frequency/crystal requires spotting capability.

To add a spotting switch to the 815 transmitter I'll try a DPDT switch connected in the cathode circuits of both the oscillator and the final. In the "spot" position it will key the oscillator just as the key and also open the cathode-to-ground connection on the 815. The crystal oscillator should operate normally letting me locate myself in the band but I'll not have 50 watts of RF overloading my receiver.

Thursday, March 22, 2007

Another layout

Here's another thought on layout ... move C2, the final plate tuning cap, from on top of to under the chassis. This frees up space top side and there is still enough space below for the parts around the 815. C2, a major shock hazard, is now safely under the chassis. I also found ceramic plate cap connectors for the 815. L4 is still exposed with voltage on it but it is set back from the edge fairly well and it is opposite the crystal socket.

Wednesday, March 21, 2007

815 Xmtr - Safety mods

Someone asked me about modifying a vintage design in the name of safety. Sounds like a good idea to me. I already modify vintage receiver projects to keep B+ out of the headphones ( see ). I also try to keep transmitter B+ away from accidental touching. This design, unfortunately, has 500 VDC exposed on the final tank coil and C2. I plan a couple of things to to help. First a front panel. I'll probably use a piece of masonite painted wrinkle black. As a bonus this gives me room for a plate current meter should I decide to add one. The second modification is to move the crystal socket to the front panel. No need to be reaching around behind the front panel to change frequency. The rest needs to be handled by being careful. Obviously power down when changing bands and short the tank coil to ground before touching it. Not so obvious is the key. Cathode keying allows one side of the key to float to B+. Usually one side of a key is more protected than the other. Connect this side to R1 and don't diddle with the key contacts with power applied.

Tuesday, March 20, 2007

815 Xmtr Parts Subbing

As I search for parts, the topic of subbing parts has come up, particularly for C1 and C2. Miniture 140pf dual section variables are called out for both of these. In my junque box I fine slightly larger (physically) parts and, for C2, only a 100pf dual section variable. I can probably work around the 100pf problem by adding two fixed 50pf caps to L4, a 80JVL plug-in coil. The physical size increase appears to be OK for C2 but C1 is going to cramp the wiring around the oscillator stage. Can I shift C1 to tune L2 rather than L3? That reduces me to needing only a single section variable. Unfortunately is also means that I need to insolate "C1" from ground. The mounting starts to take up any space that I saved by changing to a single section cap. Looks like I'll stick with the parts I've found and just carefully lay out the oscillator stage in the space I have.

Monday, March 19, 2007

815 xmtr

I'm to the point of starting to layout my 815 transmitter. Here are a couple of figures from the 1943 ARRL handbook describing this transmitter along with a picture of my preliminary layout. My chassis is 3"x 8"x12" so I have a little more room. Good thing, since I didn't have the small size variable caps called out in the original design. I'm also allowing room for a VR150 (seen on the back left corner) in case the oscillator stage needs regulated B+ for stability. The original design used only 3.5MHz crytals to cover 80, 40 and 20. I'm going to use 3.5 MHz crystals on 80, 7MHz crystals on 40 and 7MHz crystals on 20. This leads to one change. I'm adding a switch across L1/C3. This will be used to short out the cathode coil/cap when I'm running the tri-tet oscillator straight through.

Sunday, March 18, 2007

815 transmitter

According to the 1942 ARRL Handbook the 815 requires less then 2/10 of a watt of drive. A 6L6 is rated for much more than that. The 6V6 has the same base pinout but lower rating. I'll switch over to a 6V6 for the oscillator stage. My power supply will deliver about 500 VDC for the 815 but I don't want to run the 6V6 at 500 volts. I'll need to somehow drop 500V down to about 150 VDC for the oscillator stage. Depending on current requirements a VR150 and a dropping resistor might work. I don't want to use just a dropping resistor since then the 6V6 plate voltage could go as high as 500VDC with the key up.

Saturday, March 17, 2007

6L6 - 815 three band xmtr

I've always been interested in the 815 based 50 watt transmetter that showed up in QST and the ARRL handbooks just before WWII. The 815 is a dual "beam" tube designed for UHF (150 MHz in 1940). I'm starting to plan a tramsmitter using an 815 as a push-pull final (as shown in Feb '41 QST) driven by a 6L6 tri-tet oscillator such as used by Millen in his 6L6-807 rack moount transmitter.


Welcome to my blog about my ham radio activities. Here's where I plan to "talk" about what I'm doing in the shack. Feel free to comment and/or email me if you see something of interest. 73, Niel