Shy Anne - the MT-1 saga continues

[AF9J]

Well, after numerous delays, I finally finished up recapping my HP-23A power supply.   The Cheyenne is working better, but it's still not quite up to snuff.  Grid current on the driver is still very high (over 5 mA).  Also, I can't seem to get the plate current to dip decently, on initial tune, nor reach the specified 150 mA on final tune-up.  Power output is better (12W of carrier vs 5W carrier before, and 22W on peaks [when modulating], versus only 10W or so before), but still seems kind of low.  Also, I had to run the mic gain on 70% (which seems kind of high, although for all I know this might be a characteristic of the mic I'm using [a D-104]).  It looks like I still have some work to do on Shy Anne.

73,
Ellen - AF9J

[kf6pqt]

The grid current issue is troublesome... Maybe see if that meter is really accurate, (dropping resistor?)or swap whichever tube drives the 6145... (6cl6?)  I need to make that manual into a PDF still...

I'm betting the grid drive is actually really low, which is why the final goes absolutely no where.

[K1DEU]

Ellen; What is your 6146 grid drive/current ? 2-3 Ma would be decent. With screen modulated rigs I adjust the plate tuning and antenna loading for max out On CW. Plate current dip may be a little different than maxout settings. Do not expect to get Plate Current dip on AM, as the 6146 screen voltage is too low.  With a good 6146 and plate and screen voltage and a non-reactive 50 ohm load (no reflected) I might get 75-85 watts of CW output. What is your CW power output and make of watt meter. Watt meters do not tend to measure AM peaks well. An average reading(even if it claims its a peak) watt meter might only register 20-30 watts when pump handle modulating (carrier control) output on AM. Your AM pep output should be a trace higher than your CW output, try a clean single tone whistle (no breath sound). Usually only a scope or something like an Autek WM1 wattmeter with a one second sample rate will measure your pep properly on AM. 12 watts of quiescent carrier out sounds good. How does it sound listening with headphones when you monitor it with a receiver that isn't being overloaded? If your 6146 grid drive/current is 5 Ma. You can easily dump the Q on the 5763  Plate coil (80 meters only) try something like a 100K on Wafer SB between contacts 4+5   The lower the value the less grid drive  again 2.5-3 Ma would be fine.  Set your Mike gain as high as possible without objectionable distortion when monitoring.  88,  John K1DEU

Bama .pdf schematic  http://bama.edebris.com/manuals/gonset/g66/

http://www.autekresearch.com/wm1.htm

http://www.spiritualpeaceproject.com/  and  http://hamelectronics.com/k1deu/

[AF9J]

Hi Everybody,

It's been a while since I gave an update on Shy Anne's progress.  I had some issues to take care of:

1.  Grid current was off the scale.
2.  I couldn't get the requisite 150mA of plate current the manual called for.
3.  My AM signal had a fair amount of raw AC in it.

Tube swaps in the driver and buffer tubes improved the current issues, but didn't solve them.  The AC component was still present in my signal.  BUT, examination of the voltage off of the HP-23A seemed to show the root of the problem. After recapping the HP-23A, the LV section was good - about 290V, with less than 1V of AC ripple.  The HV feed was another story. In a word, it was awful.  I only got 390V of DC, and well over 350V of AC ripple.  Something was wrong with the rewiring I did, during the recapping.  I checked and rechecked the HV section of the power supply.  All of the caps, the 100K resistors (which I also replaced), and the diodes checked out as OK.  That left other wiring issues as being the problem.  I found this to be the case.

In the HV, voltage doubler section C1 & C2 are wired back-to-back to each other.  According to the assembly manual, this is done by installing a jumper wire from the negative terminal of C1 to the positive terminal of C2.   When I first opened up the HP-23A, there was a goofy 5th capacitor lying in the bottom of the power supply, that baffled me.  I realized in short order that it was there to replace C1.  C1 was shot (so much so that it fell apart, when I tried removing it during the recap), and the replacement capacitor was oversized (it was too long to fit under the power supply cover), so the old C1 was left in place for cosmetic purposes, and the new C1 was laid in the bottom of the power supply.  When I removed the "new" C1, I basically just cut it out, not taking the time, to completely determine how it fit in to the circuitry scheme of things (it was late, and I just wanted to finish recapping the power supply, so I was rushing things).  As a result, I missed the jumper wire I needed between C1 & C2.  I installed the jumper, and viola!  everything now works!

I still have to back off the drive, because the grid current will go beyond the 5 mA max.  But I'm able to get the requisite 150mA of plate current, with the grid current backed off to 3 mA.  The carrier output seems to be about 20-30W.  CW seems to be about 50 plus watts.  I did monitor my signal in the SX-96.  The raw AC is gone.  Audio seems to be OK (albeit a bit trebly - maybe a D-104 isn't the right mic for the Cheyenne audio wise).  I just need to try her out on the air.  So far, she seems to be working OK.

Now I just need to determine, why the Globe Scout 680 I bought as a provision against Shy Anne having even more problems, has no grid current/drive at all.  It was packed a bit too lightly for shipping (only newspapers around the rig, and in a single walled cardboard box, that was all banged up when the rig arrived on Saturday).  Externally the Scout 680 is in OK shape, and the controls didn't get jammed (they move freely) from movement during shipping.  But, it's possible that the rig moved around enough to affect things internally. Hopefully, it's just a simple thing like a tube getting jarred loose.

73,
Ellen - AF9J

[K9TR]

Ellen,

Congrats on the success with Shy Anne and her HP23!  I've had similar situations here with some of the longer-term repair projects (like my CE-100V).  I've learned to keep an accurate lab notebook and jot down some notes every time I do anything with one of the old rigs.  Otherwise, I'll tend to forget that I removed/disconnected/bypassed something or another over time, resulting in much head-scratching when I return to the boatanchor.

A D-104 will likely sound as you describe without some audio chain modifications.  Increasing whatever resistance Shy Anne terminates the mic with will usually provide more bass response "up front". 

Have fun with the now-working classic Heathkit!

Mark K9TR