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Friday, October 11, 2019

Winter Operating Events

The first of this winter's Classic/Boat Anchor Radio operating events is on the  horizon, only a few weeks away. I've been working on rigs since last spring. Now I'll have more chances to put them on the air.

First up is the AWA Bruce Kelley Memorial CW QSO Party in early November. This one requires that transmitters be of 1929 or earlier design and use tubes available in 1929. I'll use my Push Pull Colpitts with either an SW3 or my Simple Superhet. If things get really tough I'll move my KX3 over for the receiver.


Next is the ARRL Straight Key Night on New Years Day (UTC). This is ARRL's "Uncola" of contests (Does anyone remember those Uncola 7 Up ads?). It runs for 24 hours and has no scoring, only interesting QSOs. I'll probably bounce between several rigs but I think I'll have my Drake 2NT and R4B running as the primary station.



Right after SKN, in mid January, is the AWA  Linc Cundall Memorial CW Contest. In this one extra points are scored for rigs designed before 1950. I've three stations that would fit but I've just gotten my National FB7 checked out and running again. I'll operate it with my "CW Jr" as a 1934 station.

Next is the Novice Rig Roundup. The NRR emphasizes rigs from the early Novice era when novices had to be crystal controlled and run only 75 watts. My Heathkit HW16 is newer for me so I'll run it on 80 and 40 for this event. The backup receiver will be my KX3.



Finally, the AWA John Rollins Memorial DX Contest is in mid-March. This one emphasizes contacts on 40 and 20 using rigs designed before 1960. I'll have a chance here to use my Collins 75A4 with my Eico 720. This may not be a real DX station but, for me, it has a lot of class. 


Listen around and participate. All of these except the
Bruce Kelley Memorial CW QSO Party allow you to join in using modern gear . If you hear me give me a call. 

This winter should be a lot of fun.


Friday, September 20, 2019

FB7 / Parallel 46s Station On the Air

This week I finally finished up my early 30s CW station using a National FB7 and a homebrew 1934 transmitter. To-Dos that have been slowing me down are recapping the FB7, making a new power cable (and repairing the FB7 power cable) and then shoe horning everything into the corner I  have available for it. Does anyone else have a shack that reminds them of the old advertising slogan: "There's always room for Jello"?

I got on the air looking for signal reports and  RBN feedback. I had three QSOs that night (N4EDE/NC, W9BRD/NJ, W5RG/FL). All reported that my 10 watts sounded fine. W9BRD, even gave me a "first rate note" comment. 27 hits on the RBN said I was also getting out. Great! I've another fun station to put on the air and it is a perfect match for the January 2020 AWA Linc Cundall CW Contest.

What next? The AWA Bruce Kelley1929 QSO Party is coming up in November. I better get my  Push Pull Colpitts transmitter back on line, tested and ready to go.

Saturday, August 24, 2019

Drake 2-NT Transmitter

Last week I traded some of my 1930s heavy metal for a Drake 2-NT novice transmitter. At this point I'm interested in a decent rig I can carry rather than heavy weight shelf queens that need the next door teenager to get them out of the basement. What a great trade!

The 2-NT was introduced in 1966, late in the classic novice era when novices were still limited to 75 watts CW only and transmitters had to be crystal controlled. Around 2500 were produced. Within the novice restrictions the  2-NT had features that put it far above the competition. It was comparatively compact, included QSK or semi-breakin transmit/receiver switching and had receiver muting. Also, 80 through 10 meter coverage made it attractive beyond the novice license. The keying is set up so that the oscillator runs with a settable delay and the buffer stage is keyed to minimize chirp. Drake did a fine job with this rig.

The 2-NT was introduced with the Drake 2C but the 2-NT works well with a lot of radios that have a built-in mute function. The receiver mute function just needs to be designed so that the receiver mute terminal is grounded for receive and left floating for transmit.  This includes the Drake 2B, the 4 line (R4, R4B, R4C) receivers and the SPR-4 receiver. WARNING: Drake did this by wiring the mute function into the AVC circuit. Some radios may do this by controlling the receiver B+. I'd be careful running receiver B+ into my 2-NT.

Now I needed to decide which receiver to pair with the 2-NT. While a  2C would be nice and would cosmetically and market wise match the 2-NT, I don't have one. I do have a 2B, an R4B and an SPR-4. The 2B is a nice radio but it is of the previous generation. For now I'll leave it paired with my Eico 720. The SPR-4 is the same design vintage as the 2-NT and was Drake's first all transistor receiver. It is a fine example of what can be done with transistors in the mid 60s. Unfortunately Drake designed the SPR-4 as a high end SWL receiver. They didn't give me enough knobs to play with. AVC, bandwidth and passband are all fixed depending on the mode (USB/LSB/CW/AM) selected. Unfortunately the CW passband (and, therefore, the peaked CW pitch) is fixed at a higher pitch than my ears like. The SPR-4 went back on the shelf, possibly to wait for this winter and VLF experimenting.  The R4B has adjustable bandwidth and passband along with AVC choices and it is of the right vintage. Like Goldilocks I found my third choice, the R4B, to be just right.

Together the 2-NT and R4B work great. I'll certainly have them on the air a lot.

The 2-NT is also featured in the Sept 2019 issue of QST, Classic Radio column.

Monday, July 22, 2019

Push Pull 45s

In the November 1955 issue of QST I found this accolade to the Push-Pull TNT transmitter:

A Pair of 45s in Push-Pull
The words of
Keith S. Williams, W6DTY
 
 
The other day a few of us were sitting around chewing the fat, mostly cussing QRM, 'phone, c.w., single sideband, narrow-band f.m., Novices, old timers, the FCC, the ARRL, and the like. Joe Twerp, a ham of fairly recent vintage, remarked, "Seems like everybody you work nowadays has a Monster III transmitter. I'll bet it's used by more hams than any other single rig in the history of radio."

There was a general nodding of heads, all except for me and Hiram C. Hartley. Hiram turned to me and said, "Keith, do you recall the 'Complete Amateur Transmitter for Forty-Five Dollars'?"

"I sure do!"

History's Most Popular Ham Transmitter was first described in QST for November, 1930, in an article by George Grammer. Its immediate popularity was due to several causes, probably the most important being the Depression. It was pretty tough to keep beans on the table and a signal on the air at the same time. The standard transmitter of the day was a single 210 tube in a Hartley oscillator with 550 volts on the plate. This was a self-controlled transmitter, by the way, directly or inductively coupled to the antenna. Only rich guys had crystals and only a few were so far advanced technically that they could build a transmitter with two or more stages. Type 10 tubes cost money, and the power supply necessary in order to get decent output was almost out of the question for the majority of hams, whose billfolds were completely flat. A majority of broadcast receivers in 1930 used a pair of 45s in the audio output stage, with a Type 80 rectifier in a 350-volt power supply. Therefore. 45s and 80s were comparatively cheap and plentiful, and the corresponding power supply components were easy to acquire. The Type 45 had been a widely used audio tube for some time, but the manufacturers stated emphatically that the tube was not suitable for use as an oscillator so hams hadn't tried it in transmitters.

Grammer's article in QST stated that all parts for the push-pull 45 rig could be purchased new for $45.00 or less. Actually, the only parts ordinarily bought and paid for were the power transformer, filter choke and wet electrolytic filter condenser. All other parts, including the pair of 45s, were usually scrounged. (Many were the families who couldn't hear Morton Downey because Junior had pinched the 45s out of the family BC set and was upstairs stoking them up on 80.) In some cases the quarter-inch copper tubing for the tank coil had to be bought, but even this item could usually be managed without breaking the piggy. bank. The rig was built on breadboard. Well, it was actually built on anything handy, but rigs in QST were always built on real, honest-to-gosh. breadboards — the kitchen-cabinet variety. It was a push-pull self-controlled oscillator. It had a medium high-C plate tank for a modicum of frequency stability, an untamed grid coil, an antenna tuning condenser, and two or three small parts. It was simple to build and sure-fire in operation — the answer to a ham's prayer.

The appearance of this rig in QST coincided with a tremendous upsurge in the ham population. With the Depression, a large number of people found themselves with time on their hands. Those who couldn't get a steady job selling apples began to take up inexpensive hobbies in order to keep occupied while waiting for the NRA and the return of beer and light wines. Ham tickets began to be issued in droves. Commercially built ham gear, except for a few items like the National Thrill Box and the Pilot Super Wasp, was almost nonexistent and it was a rare would-be ham who could afford ready-made equipment, anyway. However, with Grammer's contraption you could get on the air for next to nothing and enjoy the thrill of talking to distant places by short-wave radio! Practically every new ham built the push-pull 45 transmitter and started out pounding brass on 80-meter c.w. Old timers who built a new rig in those days usually ended up with a pair of 45s in push-pull. Beginners generally started on 80 meters because self-excited transmitters usually tended to behave in a civilized manner on that band but could be unmanageable brutes on the higher frequencies. The push-pull 45 rig I had on the air in 1932 was very tame on 80 — most of the reports I received were either "PDC" or "NDC" and once in a while some liar would give me a "XTAL PDC" report and I would like to bust with pride. But on 40 meters, although the rig put out gobs of r.f., the note sounded like a buzz saw ripping through knots; on 20 meters the 45s ran red-hot and smoking while putting out about two watts to the antenna. I must say others had better luck.

Yes, indeed, that push-pull 45 rig was without doubt the most popular ham transmitter ever to be seen in W-land. After Hiram C. Hartley mentioned it the other day I got to pawing back among the stacks of old QSL cards stowed away on a closet shelf. I picked up a batch of old cards, circa 1932. Out of the first 38 cards, 24 cards said, "XMTR: PAIR 45s IN PP." That's 63 per cent, and I can easily believe that from 1931 to 1934 at least 63 per cent of all hams in this country were using that identical rig.

( Reprinted with the permission of the ARRL. Copyright ARRL.)

Wednesday, May 1, 2019

A fix for drift?

Does anyone else have a slow drift problem with their Hull Hartley? I was looking at mine and spotted something I wanted to check into.

The center tap resistors for the filament are mounted right under the tuning cap. Any heat they generate goes right to the tuning cap. Hull suggests 50-200 ohm resistors there. I used a couple of 40 ohm resistors thinking that as long as my power supply can handle the extra current draw I'd be ok. Now I have a .7 watt heat source where Hull's design had as low as a .14 watt heat source there. Any heat might cause a problem. oops.

These two resistors are in the circuit to provide a ground point for cathode keying, but there is an alternative. I have a center tapped 7.5 V filament supply. I can remove those two 40 ohm resistors and just key the filament transformer center tap. The heat source will be removed so my Hartley should now stay on frequency better.

*** clock ticks while solder smoke rises ****

Well, I removed the 40 ohm filament center tap resistors from my Hull Hartley. It is a fairly clean change. The only visible indication of the modification is the addition of one fahnestock clip along the left side for the transformer center tap connection. Now that heat source is gone.

I did before and after standby drift measurements. After tuning on the rig I checked the transmit frequency every 30 seconds for 15 minutes. Key down was only long enough every 30 seconds to get a transmit frequency readout. I had no load connected and the plate current was about 18mA with 300 volts B+.

Was is worth it?

*** Now drums rollllll ***

It depends

On 80 meters I found that the original Hull design drifted about 2KHz from a cold start while the modified version drifted about 500Hz. That's good but both took about 15 minutes to settle down. With both versions I still have to be careful about jumping on the air right after power on. I saw no significant change on 40.

But two parts were eliminated along with some amount of power on drift, both good things.

If I were starting out now building my Hull Hartley and I had a center tapped filament transformer I'd make this change. If I already had my Hull Hartley up and running, I'd probably let it be.

Tuesday, April 16, 2019

Push-Pull Colpitts Transmitter - 8

I've had my Push-Pull Colpitts on the air now for about 3 weeks and 10 QSOs. Notable QSOs have included my friend Lou, VE3AWA, in Ontario and W0NYQ, a fellow Minnesotan with a big interest in '29 rigs.

This tranmitter is a keeper. Why?

- Efficiency is 50-60% (great for a '29 power oscillator)
- Drift is measured in the 10s of hertz range. Essentially solid as a rock.
- No hand capacity problem when tuning to get on frequency
- Easy to adjust feedback for minimum plate current and best performance
- "Perfect sounding 1929 signal"

I did receive a report of a trashy buzz on my sidebands. Since then I've been more careful when adjusting the feedback and also the output coupling. I haven't had any other bad reports.

I do still have some trouble with FMing/wobble due to the wind blowing around my antenna.  This is a common problem with '29 power oscillators. Whether this is an improvement over my other '29 transmitters, I can't tell.

I haven't cleaned it up on 40 but I can work on that later.

All in all, a really satisfying project.




Friday, March 29, 2019

CW on 3565 KHz


Push-pull Colpitts power oscillator on 3565KHz with 6 watts into a low endfed wire as copied by VE7SL in British Columbia, 1490 miles to the west:

Monday, March 25, 2019

It's on the air!

It is on the air! This evening I had a great 80 mtr QSO with my friend Lou, VE3AWA, in Ontario, 570 miles as the crow flies. He reported a perfect sounding '29 signal. My Push-Pull Colpitts Power Oscillator is also amazingly stable. Even from a cold start it is on frequency.

I plan to leave it set up next to my Novice Rig Roundup operating position so that I can put it on the air whenever I want to.








Friday, March 22, 2019

Music to my ears

It works!


Last night I completed the under-the-chassis wiring of my Push Pull Colpitts transmitter. I ended up doing "bus bar" wiring. It gives a 3D effect and worked well for this design/layout. Between that and the wooden chassis this one feels like a '29 transmitter. Most of the under the chassis parts are 40s vintage but, hey, they will be hidden.
 This morning I connected power for an initial checkout. With 300V on the plates and about 20 watts input I'm getting over 10 watts out of sweet sounding RF on 80. The grounded tuning/tank capacitor effectively eliminates the detuning effect of hand capacity and I'm certainly not going to complain about 50% efficiency. Open circuit voltage across the key terminals is only 48 volts so that's good too.

 Next I'll clean up the operating position and finish my 40 mtr coils so that I can test it there.

Sunday, February 24, 2019

Push-Pull Colpitts Transmitter - 4



In between shoveling snow and chipping ice here in Minnesota (a common winter pastime and good way to catch up with the neighbors) I've continued to make progress on my push-pull Colpitts oscillator/transmitter. I've now got all of the above board parts mounted and wired  (except for the filament and B+ connections).  It is looking pretty impressive.

Along the way I've found that Lowes here in Rochester has the best selection of brass nuts, bolts and screws while Albany County Fasteners  has the best selection of specialty brass hardware like knurled nuts and wing nuts.


Next I need to plan the layout of the small parts that mount underneath.

Saturday, January 26, 2019

Push-Pull Colpitts Transmitter - 3

I'm making good progress on my new transmitter.  With a lot of help from my friend KE0EXE and his table saw I now have a nice looking oak base. I went ahead and shellacked it so that it looks pretty good. 3/16" copper tubing for the antenna link and 80 meter coil was not available locally so I have to go to Amazon for that but I did find 1/4" tubing for the 40 mtr coil at my local big box hardware store. I added a National type A vernier dial to the Cardwell tuning capacitor. This should help a lot getting on frequency.

The next task is to find all of the screws, nuts and bolts that I need and then start fastening everything in place.

Monday, January 14, 2019

Push-Pull Colpitts Transmitter - 2

I think I have enough to get started....

The tough part to find was the dual 500 pf Cardwell capacitor. I found one by putting my need out on the AWA Group Yahoo group. What I now have isn't exactly what QST called for but should be close enough. A trip to Menards got me wood for a base. I'll need to pay a visit to a friend with a table saw. Copper tuning I should be able to find locally at Menards, Lowes or Home Depot. The small
parts under the "chassis" I should have on the shelf.

Next step is to cut and varnish the base.

Sunday, January 13, 2019

Push-Pull Colpitts Transmitter - 1




I’ve started on a new transmitter for the next AWA Bruce Kelley 1929 QSO Party. The “BK” requires non-crystal-controlled transmitters that are of 1920s design and use tube types that were available in 1929. I found a transmitter described in the January 1934 issue of QST that meets these requirements.

For a good over view of the transmitters built to be used in the BK take a look at VE7SL’s gallery page at https://qsl.net/ve7sl/29gallery.html . Of the 65 transmitters 48 are either Hartleys or TNTs. The next one in the  list was the TPTG with 9. Only 2 were Colpitts. I have TNT and Hartley transmitters for the BK and a TPTG is a lot like a TNT so building a Colpitts for the BK sounds like a good next choice. This will round out my 1920s “big three”.

The 1934 QST article lists several features of this design that sound attractive:

Antenna coupling to the non-plate portion of the tank coil. The more common link coupling to the plate ends of the tank coil results in more second harmonic output and less frequency stability when the antenna is tightly coupled for maximum output. Center/swinging link coupling should be an improvement.

Push-pull tube capacitance in series. Temperature changes within the tubes that impact the interelectrode capacities will have less impact on frequency stability. This configuration also reduces the amount of current through the tubes.

Symmetric layout. A symmetric layout is less prone to exhibit signal instability

Grounded tuning capacitor body. In this design the tank tuning capacitor body provides shielding so that hand capacity has less of an impact on frequency. This transmitter should be easier to get on frequency.

Easily converted to an amplifier. If I decide to move on to a MOPA BK rig this will be one section that I already have.


In addition to information about this particular transmitter design, this QST article also gives hints that are useful for any 20s transmitter:

Use a well-regulated/stiff power supply

Route power and antenna cables away from the transmitter

Do not place the power supply close to the transmitter

Now, may the parts hunt begin!