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.

AWA Bruce Kelley 1929 QSO Party

Last weekend and this coming weekend was the AWA Bruce Kelley 1929 QSO Party. For this event only transmitters of 1929 (or earlier) design/technology are allowed. I try to participate every year. See http://w0vlz.blogspot.com/search/label/AWA%201929%20CW%20Contest .

This year I again started out trying to get my Hull Hartley to sound reasonable on 80 and 40. See http://w0vlz.blogspot.com/2009/10/more-1928-hartley_21.html Somehow since 2009 something has changed giving my Hartley a raw AC buzz and some signal drift. Swapping out parts/tubes and cleaning all of the contacts did not help. As a final effort I moved the entire station away from the shack outside wall (nearest the antenna). It still drifted and had a  T7 to T8 tone...it went back on the shelf and down came my trusty TNT.

This coming weekend I plan to be on 80 with my  210 x 2 TNT running 10 watts in and about 3 watts out. The receiver will be my KX3 with PX3 panadapter. I've given up on using a vintage receiver for the BK. 80 meter noise is pretty loud here. I need all the help I can get to hear anyone. Visible in the photo besides my TNT transmitter and KX3 receiver with PX3 panadapter is the backside of my regulated HV power supply. The wood box visible in the near left encloses my 2.5/7.5 V filament supply. In the milk crate is a QRP watt meter and Triplet milliampere meter. Notice that I have a shaft extension on my TNT transmitter. This rig is sensitive to hand capacity. Moving my hand close to the normal tuning knob changes the transmitter frequency making it difficult to zero beat another station without this extension.

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.)

On the Air with my Hartley

The AWA 1929/Bruce Kelley CW Party is coming up the first two weekends in December and the weather has started to cool off here in Minnesota. I've put the K1 back into it's winter operating position (a top the 75A4) and started to warm up the classics.

Right now I'm running my Hartley paired with my 1940 Simple Superhet. They make a good pair but my signal reports remind me of one of the Hartley's main limitations. On the 18th I worked Lynn, NG9D. Lynn commented that my signal had a fast QSY to it. Last night I worked Dave, WA9DOF. Dave reported that he wouldn't have known the transmitter was a vintage rig if I had not told him. The difference was the wind. Last night we had no wind here while on the 18th the wind was 10-15 mph. The antenna blowing in the wind shifts the load slightly that it presents to the transmitter. This in turn pulls the frequency slightly. Lightly loading the rig when tuning up helps (see my Nov 16, 2009 Blog entry) but wind can still be a factor. Pulling my wire antenna tighter or a completely new antenna might be needed. I'll see what I can do.

1928 Hartley / AWA 1929 B Kelley QSO Party

The past two weekends gave me a chance to get some more operating time on my 1928 Hartley transmitter. These were the weekends of the AWA Bruce Kelley Memorial 1929 QSO Party . The first weekend I used my HRO Sr with the Hartley. On the second weekend I paired my Drake 2B with my Hartley. I had a good time working other '29 transmitters in Minnesota, Wisconsin, Illinois, New Hampshire, North Carolina, Ohio, Ontario and British Columbia.

In total I made 16 contacts and learned a little about the limitations of my station. First, I really need a higher antenna. My antenna is a 105' inverted "L" only about 10' to 20' off the ground. It loads up nicely but, given this low height, has a fairly high angle of radiation. It probably qualifies as a Near Vertical Incident Skywave (NVIS) Antenna. Out of my first six contacts, five were here in Minnesota and most of them reported a strong signal. I also found that the best time was late afternoon, not the night time hours. The first weekend the only QSO I had outside of MN was with Ohio and it was when the QSO Party rules allowed me to crank the power up a little. When the propagation changes my antenna works OK but I feel it does limit me. Next, I learned that 40 meter transmitter performance is a little down from 80. While I've received a good signal report on 40, I can't get as much power out and I had more trouble getting on frequency. My Hartley is a usable 40 meter transmitter but 80 is definitely its better band.

1928 Transmitter Tuning

Ross Hull's QST article documents a lot of experimentation done to understand the behavior of self-excited oscillators. Whether Hartley, Colpitts, TPTG or TNT Hull concluded that all of them behave about the same and the same tuning guidelines apply to all of them. In summary, any self-excited oscillator should be run at only about half power in order to produce at acceptable signal.

After the transmitter is on frequency and running at full plate voltage:

1) Tighten the antenna coupling as much as possible. In the case of my transmitter this meant moving the antenna coil until it almost touched the tuning coil. At maximum antenna coupling tune antenna loading for maximum output and note this "maximum output".

2) Back off antenna coupling to 75% maximum power (watts) or 85% output current (RF Amps) retuning antenna loading along the way.

3) Once you are at 75% power (or 85% RF current) output, detune antenna loading by adding capacitance to reduce output another 75% power (or 85% RF current). After detuning check your signal. In some cases Hull found that detuning antenna loading worked best if capacitance was reduced rather than added.

Hull plotted frequency vs load capacitance. His curves show a fairly steep curve around resonance and then they flatten out. When a self-excited oscillator is peaked up for maximum output any changes in antenna loading will have a maximum impact on frequency. At this tuneup point an antenna swaying in the wind (changing the load that the transmitter sees) will have a maximum impact on the signal frequency. Detuning the output the oscillator away from peak output moves the operating point to the flatter part of the frequency vs load capacitance curve. Antenna sway will have less impact.

1928 Transmitter Signal Quality

Ross Hull's August 1928 QST article, "Overhauling the Transmitter for 1929", is a great article for anyone interested in putting a late 20s/early 30s self excited oscillator on the air. This includes the Hartley, Colpitts, TPTG and TNT transmitters used in the AWA Bruce Kelley 1929 CW Party. In the words of QST, this "is, we feel, one of the most important articles ever published for the radio amateur. Let every amateur study it most carefully, and apply its information, for it contains salvation for 1929." It can be found by searching the QST magazine article archives at http://www.arrl.org/.

Ross Hull's major point is that the poor signals legal in 1928 will no longer be acceptable in 1929. He further states that the main problem is the "men pushing the keys". How 1929 transmitters are tuned up makes a big difference in signal quality. The actual transmitter required to meet 1929 standards can be fairly simple. To prove his point he describes the one I built, a "simple -- in fact crude -- rig...capable of performing quite creditably". He even goes on to say that he anticipates some "raspberries" over the crudity of his simple transmitter.

Transmitter features helping signal quality include a heavy tank coil/circuit, mounting the tube so tuned circuit heating is minimized and high tuning capacity/low inductance. Ross Hull emphasizes that the inexpensive hardware features he's listed combined with proper tuning over come lots of the frequency shift introduced by marginally filtered or unregulated B+ supplies, antennas swaying in the wind and components heating up. Simple 1929 transmitters don't need to "splutter, wobble, creep and rattle across great slices of the bands".

In fairness, I still find that moderate winds causing antenna sway does introduce some FMing, but my signal is acceptable. Hull, in fact, states that a DC (T9) note is extremely uncommon and rather unpleasant. He much prefers a more "musical note" that we might rate T8. Given proper tuning that's about where mine is: a sweet, musical, T8 signal. Also keep in mind that this transmitter design does not address other "creature comforts". It is microphonic requiring it to be placed on a table separate from the operating position, hand capacity is a problem and bandspread, such that there is, is barely adequate for getting on frequency. These could be addressed in a more expensive design but their solution is not required in order to archive "any reasonable [signal quality] standard set for 1929".

1928 Hartley Coils

Pictured are my 80 and 40 meter tank coils. Ross Hull made a strong point in his QST article that these coils need to be able to handle a lot of current (5 amps of RF for this design), be mechanically stable and tune with as much capacitance as possible.

These coils were wound out of 1/4" OD copper tubing. A piece of 2 3/8" OD pipe was used for a winding form. Once a coil was wound I installed it and then adjusted the turn spacing so that the bottom edge of each band fell close to maximum tank tuning capacity.

While shopping for copper tubing I found that tubing wall thickness varied brand to brand. For best current handling and mechanical stability I bought the heaviest/thickest I could find.

More 1928 Hartley

The last few evenings have included some final cleanup of the Hartley and then getting it on the air some more. There's been several of us on 80 meters around 3615 during the late evening but the 80 mtr propagation god hasn't smiled on me since my QSO with VE3AWA. Some of the others have heard me but I haven't worked anyone. Hear is how I sounded last night at VE7SL's QTH in British Columbia by clicking here.

More 1928 Hartley

Well, it's in the log...the first QSO. Tonight I worked Lou, VE3AWA, on 3565. We were 549-559 both ways and had a nice contact going until 80 meter QRM caught up with us. Lou was using his Push-Pull TPTG transmitter with a NC101X. I had my HRO Sr paired with the Hartley running 10 watts input and about 3 watts out.

For this contact I added an extension to the main tuning capacitor shaft. Both my TNT and this Hartley are really sensitive to hand capacity. Adding 8" to the tuning shaft helped a lot as I moved onto frequency. I also used a VT-25, the military version of the type 10.

Not obvious in the Hartley list of parts are the National Velvet Vernier dials used by Ross Hull. These make a big difference adding mechanical bandspread to help overcome the 80 meter CW band being crammed into a few degrees of capacitor rotation at one end of its travel.

Lou asked how come my signal was so stable. Antennas swinging in the wind typically shift the transmitter frequency as the load changes. My 105' inverted "L" happens to be a little low (only 10-20' off the ground) and behind a ridge so it is protected from the west winds. I also run with the antenna loosely coupled to the transmitter. Output is only about three watts instead of the 5-6 watts the transmitter is capable of at maximum coupling.

The RF choke is now one I hand wound on a 3/4" piece of wooden rod like Ross Hull's original 1928 design. It doesn't have quite as many turns as he called for but it works fine.

More 1928 Hartley

After a little debugging it works!

When I first put power to my version of Ross Hull's Hartley transmitter I could only get it to oscillate if the cathode clip is either not attached at all or clipped to the tank coil near the plate (rather than grid) end. RF with the clip this high on the tank coil is detectable on a nearby receiver but not measurable at the transmitter antenna.

It turned out that all things that look like RF chokes don't make good RF chokes. Mine from my junque box looked like a single layer vintage RF choke, it tested good for continuity and B+ showed up at the tube socket but didn't work well in this circuit. Replacing it with a
more modern RF choke fixed my problem. I'll need to go back and hand wind one like shown in the original 1928 QST article.

I also needed a 4:1 balun to match well to a 50 ohm load.

Now with 300 V B+ and about 25mA input I can push it to over three watts out. Backing off gives me a clean 2 watts out.

Thank you to several AWA friends that helped with parts and advice.

 

More 1928 Hartley

Except for a couple of coil clips my clone of Ross Hull's 1928 Hartley is complete. It's ready for power and checkout.

More 1928 Hartley

Today we have surface-mount-technology, before that we had pin-in-hole printed circuit cards, before that point-to-point wiring and before that we had breadboards. With breadboard construction came solid bus bar wiring. Bus bar is stiff enough that wiring takes on a 3D sort of aspect. Wiring of a transmitter such as this Hartley has height along with depth and width.

More 1928 Hartley

Working through this project has given me a new appreciation of the homebrewing skills of many of the hams during the twenties and thirties. The article on this particular transmitter has some gaps in the construction details....for coil turn information the builder is referred to the coil photo, to count the turns himself....and....Keying method is a reference to another chapter and, again, left to the builder to figure out.

I chose cathode keying for my version. I also buried the cathode resistors under the tuning capacitor. Keying added two additional Fahnestock clips along the left hand side. From the front mine lays out as keying (hot side), keying (ground side), filament, filament, B-/ground and B+.

More 1928 Hartley

That pile of old parts, wood and copper tubing is starting to look like a transmitter. The eight parts left are mostly to be wired into place so things should speed up a little.

The unsung hero of any project like this is a drill press. Without one you could never get all of the holes right.

More 1928 Hartley

With (plexi)glass rods ordered and one additional National DX capacitor in the mail from a friend the next step is some table saw time.

A 1928 Hartley

After seeing my 1934 transmitter a friend asked if I was doing anything special for the Bruce Kelley Memorial 1929 QSO Party coming up in December. Last year I put my TNT transmitter and SW3 on the air. This year it might be interesting to try a Hartley oscillator.

As ham radio approached January 1, 1929, and the more rigorous standards, the ARRL encouraged hams to improve their stations. One improved transmitter design was a single tube Hartley oscillator described by Ross Hull in the August 1928 issue of QST. Bruce Howes, W1UJR, covers this design on his web site here.

I've been searching through my junque box looking for the parts I need. The first step was a parts list and an enlarged scan/photo of the transmitter. After picking through multiple boxes and peanut butter jars I've lots of possibilities. Now it's a matter of sorting through what I have for the parts that match the original design.