[Milsurplus] GO-9 Progress Report. 4 Nov 19, First Contact

[Richard]

Good work.  I have a TBW, and thought, briefly, of converting to 60 
cycles.  The biggest problem is the 60 cycle plate transformer would 
take up most of the space, not to mention a big step-up in weight.

Richard, AA1P


>
> GO-9 Progress Report. 4 Nov 19
>
> On the bench:
> https://photos.app.goo.gl/CVEUCCRUNXiVzgRs8
> Thank you to everyone who is contributing discussion and knowledge to
> this project.
> You're invaluable!
>
> Home-brewing stuff from scratch has never been a "strong point" for me.
> I begin with good intentions and a vision of this "neat and sleek"
> design with laced-cables and right-angle wires and everything easy to
> reach. Then I install  the Transformer sub-chassis and discover my "neat
> and clean" vision has collapsed into smouldering ruin; I built the
> Transformer Deck backwards, the hardware holes don't line-up and the
> "tidy" wiring harness is now a fantasy.  Not about to pull everything
> out and rebuild it; I ain't gonna live forever.  So the orderly wiring
> is now a rat's nest and spider web, which is why I'll carefully crop all
> these photos to hid the most embarrassing jumbles.  Hey- at least it's
> admitted.  And it works, so "all's well that ends well," right?
>
> The plan for the power supply is to build it in vertical layers, using
> "floors" or sub-chassis.  Some aluminium angle-stock easily adds a
> "floor" mount.  I'm no MIke Hanz when it comes to metal work,  but I did
> manage to mount it right-side-up:
> https://photos.app.goo.gl/CKjydzEpxT1JKtyWA
>
> The build-space is only 7 inches wide.  The Transformer deck is cramped
> and crowded- hard to work in there since my "master plan" turned into a
> "Mess-ter plan."   Worse- there's HIGH voltage running-around in there.
> With the gas pedal (variac) mashed to the floor, we're talking 1700
> Volts or more.  I'm paranoid about such voltages- a lot.  Have rebuilt a
> couple of Heathkit DX-100s, recovering them from the fried and ashy
> results of careless design around High Voltage, and that was only
> 8-or-900 Volts, so I kinda over-compensate. The bridge rectifier wires
> from the HV transformer secondary are triple-covered in heat-shrink
> tubing and are spaced at least an inch apart, with no sharp bends or
> proximity to grounds.  The solid terminal strip that connects the HV
> leads of the transformer to those leads will get a double coating of HV
> Varnish.  The bridge rectifier is mounted on semi-flexable Lexan sheet
> with holes drilled for the HV leads.
> https://photos.app.goo.gl/Uo8rCNamzWooaimN9
>
> The Low B+ ("Low" - That's funny.  It can go as high as 700V+ ) filter
> caps and future regulator mount on another Lexan sheet above the bridge,
> the center-tap wire passing through drilled holes in both sheets.
> Lexan is hard to cut; it's tough and semi-flexible.  You can't just
> score it- even half its depth and break it. I ended-up using a power
> hand grinder to cut it. Drilling is no problem if one uses light, steady
> pressure and patiently waits for bit heating to do most of the work.
> You can break the stuff if you force it.  The two B+ output leads also
> pass through holes drilled in the Lexan before connection to the power
> supply/Transmitter spring contacts.  Update: The Low B+ regulator may
> not be needed.  Will depend on any problems with FMing on modulation.
> We'll see.
>
> Speaking of the connections between the Power Supply chassis and the
> Transmitter chassis:  The transmitter has knob-looking posts which are
> connected by spring-contacts on the power supply:
> https://photos.app.goo.gl/k4w2VmpW6UgZvyU68
> I had to remove these spring contacts to mount the backwards-Transformer
> deck and wire it up.  If you take these things off, have a special
> holder for the hardware and remember - Long stand-offs on top, short on
> bottom.  These strips have four mounting screws with star-washers and
> nuts on the back side.  View with the right-hand strip removed:
> https://photos.app.goo.gl/Xs3wvXbhYsim9NH8A
> When you go to put these back on, it's nearly impossible to reach the
> nuts on the back of the one on the right.  I wasted lots of time and
> frustration trying to start those blasted nuts.  Hit upon an idea:  I
> layed the strip flat and put a drop of glue to the side (not in!) of
> each of the holes.  Then carefully aligned the washers and nuts over the
> holes:
> https://photos.app.goo.gl/jsEEVjxniDU7nqkr7
> The glue set in a couple of hours and held the washers and nuts just
> enough that, if you're gentle, you can get the nuts started. Only one of
> the four failed to start (the hardest to reach, of course) but did
> managed to get the strip properly remounted.
>
> Oscillator-Intermediate Amp Filaments:
> The ferrites across the High-IR-drop filament chokes did not work; it
> introduced 60Hz FM to the Oscillator.  I'm pretty sure some of you
> expected that, LOL.  Was worth trying.  With only 10 Volts on the Osc.
> filament, the drive from it is reduced quite a bit.  Not about to try to
> disconnect the wire snaggle and pull that heavy transformer deck back
> out to shoe-horn in a 15 VCT transformer, if I could find one.  Hit the
> junk box and found a little "Radio Shack" 6V transformer and hooked that
> up as a boost winding (note winding phasing).  This haywire delivers
> 11.9 V to the Osc and IA filaments and has improved drive to expected
> levels   It is small enough to tack on top of the original filament
> transformer.  "More than one way to skin a cat," they say.  Here's the
> idea being tested:
> https://photos.app.goo.gl/xBjmLr2WvuUzaSuQ6
>
> Here's a rough diagram of the power supply as it stands now:
> https://photos.app.goo.gl/4VxtZWkMEkwQhaUh7
> Haven't yet built the Grid-Block bias supply or any of the control
> circuits.   The High Voltage design uses the "Economy" principle, where
> a center-tapped transformer uses a bridge rectifier and the normally
> unused center tap provides a second DC High Voltage of one-half the
> value of the full secondary.  It needs only capacitive filtering.  High
> B+ uses six 330 uFd 400V caps with 100K resistors across them in series
> for filtering.  Low B+ uses two 120 uFd caps with 100K resistors.  This
> seems to be adequate- no hum or FM in the transmitter signal or chirp on
> keying.   I changed the panel-mounted Plate Current meter connection.
> It was originally in the Hi-B+ negative lead, which prevented having a
> meter on the front panel at full B+ (as long as the meter doesn't
> open-circuit).  I couldn't just leave it in the negative lead from the
> bridge because this is a solid-state rectifier.  The inrush current from
> charging the caps would insta-smoke the meter. Putting it in the PA
> Cathode circuit (with long, bypassed leads) solves that issue, but it
> does mean the meter is reading the sum of Plate, Grid, Suppressor and
> Screen currents.  I very carefully insulated a temporary current meter
> and put it in the Hi-B+ lead to read actual Plate Current and compare it
> to the panel-mounted meter.  At maximum rated Plate Current of 175 mA,
> the panel-mounted meter reads 260 mA.  I can live with this.
>
> You probably remember that the "keying" lead is power supply pin 17,
> which grounds the grid circuits of the Osc., IA and, in the original
> owner's "grid block keying" change, the PA grid circuit to ground.
> Review of the simplified diagram and the keying points:
> https://photos.app.goo.gl/BkRAsT5X54ozFwdGA
> I mention it at this time because, with the "keying"point left
> unconnected and no negative cut-off bias at this point, the Oscillator
> stage will start working at a low level, as do the other stages, and a
> few Watts of "Backwave" get to the load.  One of our members kept the PA
> grid circuit grounded and keys only the Osc/IA point, leaving the PA
> running unbiased during key-up.  That configuration does not exhibit
> back-wave.  Since we'll eventually be using grid-block keying, this
> won't be an issue.  Just mentioned it in case someone else runs-into
> this situation.
>
> Grounded pin 17 (keying), fired-up the power supply and the transmitter
> seems to be cooking.  Cranked on the B+ variac and "put the pedal to the
> metal," bringing the Low- B+ to the rated 550V and the Hi-B+ to about
> 1400 (estimated- my meter won't go that high).  This maxed the PA Plate
> current at 175 mA.  Tuned-up into a 50-Ohm load, measured with both my
> wattmeter and with my calibrated scope, the transmitter is delivering
> 200W+ out on 3890 KC. This seems a lot but both instruments agree.
>
> First QSO:
> Powered the B+ off and hay-wired the large Line-to-Voice-Coil
> transformer into the Cathode lead, fed it's 4-ohm tap with a small audio
> amplifier and a lo-Z dynamic mike.  Powered up and tuned-up the
> transmitter to 150W out, then cranked-up the audio until I got a nice,
> clean 100% waveform.  Cathode modulation doesn't add to the PEP of the
> carrier but that's OK.  The simplicity is worth the trade-off.  First
> contact was with local AM guru Mason, K5YHX, who reported excellent
> audio.  Kinda funny to watch as my "keying" was turning the variac on
> and off, switching the B+ just like in the original circuit.  Yes, it
> did "swoop away" for about half a second. Didn't mind.  Was too happy
> about the contact.
>
> An important point:
> It is very easy to mis-tune this transmitter and be wind-up on the wrong
> frequency.  My first tune-up turned-out to be on 5 MC. The tuning charts
> give a "ball park" for settings and should be consulted.   Settings for
> operation of this specific rig on 3890 KC are:
> A=2   B=600  C=2   D=50
> E=1  F=80  G= Just under 4MC marking
> H=Current  I=88  J=655
>
> Things are coming together.  More later.
> And I have no idea where I'm going to put this big beast!
>
> GL OM ES 73 DE Dave AB5S
>
>
> -- 
>
>
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