ad: elecraft

My First-Ever QSO -- 50 Years After Passing Ham Test

Discussion in 'Ham Radio Discussions' started by G3EDM, Aug 27, 2021.

ad: L-HROutlet
ad: l-rl
ad: L-Geochron
ad: HRDLLC-2
ad: abrind-2
ad: MessiPaoloni-1
ad: Left-3
ad: L-MFJ
ad: Left-2
  1. G3EDM

    G3EDM Ham Member QRZ Page

    This morning was spent troubleshooting, and finally solving, an annoying problem with parasitic oscillation in my regenerative receiver.

    This was a "fingernails on a blackboard" sound that could be triggered by knocking the set, or could just arise on its own. Once the oscillation started, it did not go away but stabilized at an annoying level in the headphones.

    For a full description of how the oscillations were tamed sufficiently to no longer be a nuisance, see my thread called "High Performance Regenerative Receivers" in the Homebrew and Kit Projects forum. Full details and several photos (post #49 in that thread) and also an updated schematic (post #48 in that thread).

    73 de Martin, G3EDM
     
    G0CIQ likes this.
  2. G3EDM

    G3EDM Ham Member QRZ Page

    I did read this when you posted it two weeks ago but it bears revisiting.

    As you know my current plan is to replace the Boosted Pierce 6C4/6AB4 oscillator in my "Novice transmitter" with an outboard, one-tube Electron-Coupled Oscillator with a regulated 150V on the screen. But according to your analysis above, even that will not enable stable use of HC-49 crystals for 40m (and these make up about half of my collection, including some of the most popular frequencies).

    It still makes sense to build a more stable and useful oscillator to provide sufficient drive to the 5763 in my existing transmitter. But I need to be realistic about those HC-49s: they may be properly usable only in a three-tube TX design with more like 75V on the oscillator.

    But at that point, it's the tail wagging the dog, there is no point continuing to try to modify my little transmitter, might as well build an entirely new one. (But note that this is difficult with my current non-workshop situation. Still working on that.)

    Still, I am slightly confused by your advice, because when I lowered the plate potential on the 6AB4 to a regulated 150V and ran some tests on-air with the HC-49 crystals, they performed impeccably. It's just that the oscillator provided way little drive to the PA, at that voltage. That's why replacing the Pierce with an ECO is so attractive.

    If the ECO turns out not to be usable with the HC-49s in the two-tube MOPA configuration, so be it. I do have plenty of vintage ("genuine") FT-243 crystals and could fill in some gaps by purchasing a few more.

    (All of the above is aimed at trying to operate on the air as often as possible in the next few months and not being constantly way-laid by troubleshooting and modification sagas! In the longer run, surely I ought to be able to build from scratch a much better station in the first half of next year, professional commitments permitting.)

    73 de Martin, G3EDM
     
    G0CIQ likes this.
  3. G3EDM

    G3EDM Ham Member QRZ Page

    The machine screws and nuts arrived today. Can't do tube homebrewing without those! Until today I'd been cannibalizing other projects (mostly small AM radios that I had built) but ran out of hardware to scavenge.

    [​IMG]

    73 de Martin, G3EDM
     
    W7UUU, G0CIQ and KP4SX like this.
  4. W9BRD

    W9BRD Ham Member QRZ Page

    Please let know where the confusion got in. I'm glad the 6AB4 with 150 V made the HC-49s work so well at 40 m. That's a sweet spot with that plate V plus a higher-amplification tube. The trick is getting to (a) normal class-C drive to the 5763 with those same 6AB4 operating conditions (not likely with a Pierce oscillator, which is to say "with the oscillator-final coupling non resonant") or (b) with a grid-plate power oscillator subbed for the 6AB4.

    When a grid-plate power oscillator is subbed for the 6AB4 and the 5763 grid nonresonant, I think you'll still be short of normal class C drive for the 5763, at least at 40 m. (Unless you operate the oscillator tube with higher than normal plate V. And now see (b) in the next sentence.) When you resonate the 5763 grid, I expect two effects (a) the 5763 will want to oscillate as a locked oscillator, and so neutralization will be required, and (b) the increased RF level at the oscillator plate will get more RF back to the crystal such that it chirps and yoops.

    Yes, even with the 6AG7, 6CL6, 12BY7, and lower-power relatives in play. And BTW the 12BY7 is a closer equivalent to the 6AG7 than the 6CL6 when the pivotally important characteristic of grid-plate capacitance is taken into effect. GE didn't quite get the 6CL6's internal shielding good enough to equal the 6AG7 G-P C. And BTW, tube G-P is generally lower when a tube is shielded with a close-fitting shield. (This does vary for some miniatures; the spec sheets will characterize G-P C carefully versus shielding when this is the case.) The 6AG7's metal shell makes shielding easy; connect pin 1 to chassis. For miniature tubes, we need a shieldable socket mounted to the chassis, and then the removable shield added to that.

    Shout out to the 6AG7 plate curves: See that little negative-resistance kink in the curves at highly negative grid voltages? The 6AG7 is a true pentode -- I sawed one open to check -- but its suppressor grid is just four widely spaced, wide loops far from the screen between the tube's screen and two-opposing-metal-strips plate structure. If screen-negative-resistance parasitics occur in a 6AG7 stage, a screen stopper R will stop them.

    Minimizing oscillator output and amplifier output getting back to the ocillator grid is important. On one of my development chassis, working with an available socket hole instead of punching a new one I added an 8156 final-amplifier tube (for 10 W output) a bit too close to that three-stage rig's 6BH6 oscillator. (The 6BH6 was in a shieldable socket, but not otherwise shielded.) The oscillator frequency varied a bit with final-output-net tuning. I quickly cut a suitable rectangular piece from a scrap tin remnant, fashioned a 90-degree corner shield for the 6BH6, and soldered it to the chassis around the 6BH6 and between the 6BH6 and 8156. Frequency pushing gone.
     
    Last edited: Oct 1, 2021
    G3EDM likes this.
  5. G3EDM

    G3EDM Ham Member QRZ Page

    Confusion may be the wrong way to put it. It's more the uncertainty about what the upcoming oscillator modification will achieve.

    But at the very least, I am hoping to get more drive to the 5763, which is under-driven right now. At QRP, that is a waste.

    Whether my HC-49 crystals also become usable both in terms of signal quality *and* reasonable PA drive is the big uncertainty.

    As I've said before, if that means I fall back on using only the robust, original FT-243s -- fine. It will be interesting to find out.

    73 de Martin, G3EDM
     
  6. W9BRD

    W9BRD Ham Member QRZ Page

    Another approach -- heresy (I say semi-humorously) to many -- would be to lower the screen voltage to the 5763 to the point at which the existing drive is sufficient for class C. Or bias the tube for class AB1 or AB2 operation.

    Whatever RF output you get will still be "QRP", and you'll still make contacts -- maybe not as often as now.

    There is so much lore about transmitting power that few hams can see the issues value-neutrally. How many times have we read the likes of "Doubling your power is 3 dB, which is only half an S unit, so that much power increase isn't worth it." "A 1-dB change is the minimum power-level change a human can detect by ear." And so on, and so on, and scooby-dooby-dooby. On the other hand, one's power meter being down the needle's width on one band v another means it's time for an all-out investigation.

    Communication is a competition between signal and noise -- in effect, between orderedness (the signal, at a known frequency or band of frequencies, encoded in some known way, carrying information of some expected type) and randomness (noise). The more predictable the characteristics of the signal, and/or the more distinct it can be rendered relative to noise at the receiving end, the greater the chance that communication will succeed, and/or the fewer information-recovery errors will occur.

    Our antennas emit photons. The higher the transmitting power, the greater the number of photons emitted per unit of time. In the connection of making one's signal potentially more distinct from signal, the more photons our antennas emit per unit of time (in the direction of the receiving station :) ), the better. Emitting more radio photons per unit of time increases the chances that successful communication can be be achieved.

    This is why any power increase can be worthwhile, and any power decrease can be a liability -- in terms of potential communications effectiveness, not in terms of economy, the fun of doing much with little, and so on. Any power increase increases the odds that communication can succeed. Any power decrease decreases the odds that it can succeed. Notice that in effect we're talking statistics. Statistics neither predict nor confirm individual cases. Amazing, "how'd you do that with only 1 watt?" propagation and operating-luck/skill events can occur "anytime."

    So: Maybe a 1-dB power difference is the smallest level change a human can discern under controlled lab conditions, but the phrase "controlled lab conditions" does not describe analog communication that depends on aural reception of fading signals near the band-noise level. It may be that a 1-dB power increase, or even 12 W instead of 10 W, is just the margin necessary to receive one particular Morse dot that determines whether or not you receive the other stations call sign (or you name the datum) correctly.

    At that point, all the traditional, BS-based lore about how much power increase or decrease matters flies out the window. You either receive what you need to receive correctly -- maybe with fills with the help of your intelligence and the context and/or content of the communication -- or not.

    So build/operate your transmitter at/for whatever power level seems economical/fun/possible/safe/tameable, and then go forth in ham-radio peace. Do your best; tune for max; don't allow stupid should-have-known-better sources of needless loss; and have fun.
     
    Last edited: Oct 2, 2021
    G0CIQ, G3EDM and W0PV like this.
  7. G3EDM

    G3EDM Ham Member QRZ Page

    Today was spent making a single, but very significant, modification to my Boosted Pierce transmitter.

    "Dining-room table workshop" as usual.

    I added a couple of 0B2 voltage-regulator (VR) tubes in series, under the chassis, to help deal with the ubiquitous yoop/chirp issues with this design.

    As is often the case, this proved to be a mechanical challenge more than anything else. In the end I decided to place the two VR tubes at the right-hand end of the transmitter, beyond the output tank coil. Not ideal, but all of the other possible locations were worse.

    (Similar mods have been made before but they were "outboard" and my transmitter looked like a basket case with all its pigtails and removed bottom plate.)

    I needed to create a special bracket to hold the tubes. This was done with thick aluminium and an improvised "brake" as well as a "stepper" drill bit:

    [​IMG]

    Resulting in this:

    [​IMG]

    To be screwed onto the chassis using these connectors (the headphone sidetone sockets). Reminder: I will not physically modify this "ARRL original" transmitter by drilling new holes....

    [​IMG]

    So I ended up with this very customized bracket:

    [​IMG]

    With the tubes:

    [​IMG]

    And finally, in-place (wiring not yet completed, but it was indeed completed later):

    [​IMG]

    The big issue is that for more than three weeks I have not been on the air. No QSOs, and more significantly, a sharp deterioration in my Morse and operating skills. So the idea is to get back on the air with the equipment I have -- while planning for improvements.

    The transmitter is now back on its shelf and working great, no longer a basket case.

    Major improvements in my rig are in the offing. For details (and a lot of off-topic but fascinating stuff) go over to the "Homebrew And Kit Projects" forum and scope out the endlessly meandering thread called: "Oscillator/PA Cathode Keying, 'Spotting' Your Frequency, and Chirp".

    Edited to add: In the interest of speed, I bought "modern" (made in the Far East) 7-pin tube sockets for the VR tubes despite the warnings I have heard about them. Well, the warnings are correct. IMO the "modern" tube sockets are inferior to vintage NOS. Not a major issue in this case as these are VR tubes with pure DC currents, no RF or AF involved. But I will not buy them again.

    Tomorrow: Upgrading the Transmit-Receive Switch.

    73 de Martin, G3EDM
     
    Last edited: Oct 2, 2021
    G0CIQ, W9BRD, KP4SX and 1 other person like this.
  8. G3EDM

    G3EDM Ham Member QRZ Page

    Another QSL card arrived yesterday, reminding me yet again of the need to get back on the air. Target day is tomorrow, Monday. (Today is busy with rebuilding the T/R switch in the morning, then social/family stuff for the rest of the day.)

    [​IMG]

    [​IMG]

    Looking at my notes from this QSO, you can see why it is important for me to strengthen my Morse copy skills! Even three weeks ago just before I went off the air, I was only catching the bare minimum required to conduct a QSO successfully. After the several-week gap, my skills will have deteriorated unfortunately. I think the "technical break" to improve my rig was worthwhile but it has come at an obvious cost.

    [​IMG]

    73 de Martin, G3EDM
     
  9. G3EDM

    G3EDM Ham Member QRZ Page

    Yes! Our landlord has given me carte blanche to convert the garden shed into my workshop. That includes evicting the lawn mower and garden tools, which will be housed in a smaller "garden tool shelter" that I will build nearby.

    The space is tiny, and the sloping roof is low: I'm 1 metre 93 (6'4") and can only fully stand up on one side of the "room". But it has electricity, the basic structure is OK (it is built on a concrete base of some kind), the tar-paper roof does not leak, and adding insulation and internal walls should be straightforward and not cost too much money.

    Obviously it will take some weeks to get this done, but meanwhile: Welcome to the G3EDM workshop! I might even operate from there some of the time: there cannot be too many hams who are literally operating from a shack!

    [​IMG]

    The basic plan is:
    • Seal some holes in the walls (wooden "knots" that fell out of the planks).
    • Add a layer of insulation.
    • Then add inner wall, probably plywood but with enough structural support to enable shelving and so forth.
    • Reinforce part of the floor to hold a full-size drill press with enough "swing" to work on large tube chassis.
    • Bench along entire back wall (where the height under ceiling is lowest).
    • Shelves above bench.
    • Devise some system for storing hundreds of different little parts (hardware, and small components, are the big issue). Doesn't matter what it is (discarded yoghurt pots, or store-bought drawer systems) as long as it is organized!
    • Wire the bench for both the local 240VAC and for 117 volts, to enable using my vintage American test gear.
    • Some form of heating.
    • Security: You could blow down that door with a whisper. Make it more theft-proof.
    • Very good lighting (the windows are small, and high up). Probably fluorescents on ceiling, then the usual large lighted bench loupe.
    Can't wait to get going. It will be a bit slow because I don't own a car (a lifestyle choice) so the building materials will have to be ordered online.

    There will still be challenges.
    • The shed is far too small to hold my entire junkbox, most of which will still have to be stored off site. Basically, the off-site junkbox (in a storage unit on a farm about one hour's walk from my home) will need to be properly sorted and organized on a project basis so that (1) I know what I have and (2) I know where to find it.
    • Even with good insulation, it may not be wise permanently to store sensitive gear or test equipment in the shed. Some of that stuff may have to be stored in the main house, and brought out to the workshop on an as-needed basis. (The climate in the UK is very moderate, but also extremely damp....).
    • It's a tiny space!
    Can't wait to get going!

    (Now, time to get back to the kitchen counter and finish rebuilding that transmit-receive switch!)

    73 de Martin, G3EDM
     
    G0CIQ, UT7UX, KP4SX and 1 other person like this.
  10. GM3ZMA

    GM3ZMA Ham Member QRZ Page

    My first radio activities were from a similar shed 50+ years ago.
    The shed was a bit bigger 6ft x 8ft, and in nicer condition.

    There, fixed that for you!

    Jim GM3ZMA
     
    G3EDM likes this.

Share This Page

ad: M2Ant-1