Monday, August 24, 2015

Stay tuned..

..I am about to rip a new asshole for LDG, the LDG Yahoo Group, and the IC-7200 Yahoo Group. Hint: You buy 4-5 of LDG's tuners and kits over the years and you'd think you would get a little more that shrugged shoulders and "Dunno, our LDG Z11 PRO II works on our IC-7200."

And the IC-7200 Yahoo Group ain't much better; just appliance operators.

*sigh* 

Well, maybe I am just having a bad hair day!

Tuesday, July 7, 2015

A Triplett Amongst the Simpsons

I stumbled on a decent Triplett 630 NA the outer day on eBay and scooped it up. Was in great cosmetic shape but had a few range inaccuracies and the needle stuck. So, after looking at it and considering the dirt price I paid and factoring in the skill required to remove debris from the meter movement, I packed it up and sent it off to my favorite meter repair people: Instrument Meter Services..notably Ike and Jason. It was accompanied by a symptoms report and instructions to give unto the tender mercies of their tech, John.

After a reasonable amount of time and for a very reasonable price, the unit was received back into the shack where it nuzzles up to my two Simpsons. One of 'em was a 260 I inherited from my late father and the other, a 270 I found at a swap meet -- also for dirt. Its performance is well within a satisfactory 3% of full scale at the most variant but when it counts, is dead on the money -- as are my Simpsons, by the way. John up at IMS sure knows his stuff and does good work.

But let's face it, these folks units are collectors that I value higher than what I could actually turn 'em for on eBay or at a swap, but then that's the point of collecting, innit?

Anyway, here's some shots of the Triplett and its innards. It's immaculate and one of my pride and joys:











-30-

Friday, July 3, 2015

Zuni Loop FD 2015 - A 31-year Mountain High

In a relentless endeavor to wring points out of the ether, the Zuni Loop FD warriors entering their fourth decade. Truthfully, not all of us have enlisted for the entirety of the 31 years, but some have and to those of us who have a much shorter careers, we are grateful for the privilege.

Cam Hartford, N6GA, the one of the progenitors of this Summer fete, started out the year fearful that we might be entering this effort short on depth. Our 40-meter man was sidelined with an injury and others were doubtful. But come Saturday morning, Paul, N6EV, and Richard, KI6SN, showed up to bolster the ranks. These guys along with Cam and Keith, K6SIY were present to hold down the fort on 20M, 40M, and the odd digital modes. Dick, WB6JDH, and I were detailed to nail down the fringe -- 80M phone and CW, 6M, and VHF/UHF (in which KI6SN assisted).

Table Mountain Campground trees festooned with these majestic sky wires for FD

The solar flux did not portend a momentous weekend -- hovering somewhere around 100 -- and we were prepared for the worst. But we soldiered on and when the dust cleared Sunday at 1800Z, Paul, Cam, Keith, and Richard contributed over 400 Qs on 40M CW and the same on 20M CW. Our totals were:
So, our submission will end up being 11,775 points -- said by Cam to be the highest Zuni total in the 31 years of its participation in Field Day. Excellent sampling of pictures from the venerable Jim Lowman, AD6CW.


WB6JDH's 6M and 10M Moxons

Skimpy, ad hoc VHF/UHF arrays

More FD arrays for even. Squint really hard and you can see it.

Ibidem

15M/80M CW Lair

K6WHP in situ

K6WHP FD Express

Coiling rope: anal retentiveness can be fun!

Richard at the K-2 cotnrols reeling them in on 40M CW.

Richard's "Swiss Fork" vehicular antenna?

Keith, K6SIY at the 20M position.

N6GA does digital!

Zuni Loop MEF charitable gift from the BSA.


WB6JDH's ancestral manse buffeted by the winds of war.

It's da Wolfman, babies, on N6GA for your QRP pleasure.OOOOUUUIIII!

20M K3

From the desert..

..to the trees, this is the Big 'GA comin' at you, fellow babies!

An' we be usin' the power of the sun too, fellow babies!

Only 360 days left until FD 2016!

-30-

Thursday, May 14, 2015

eBay Shills and Infomercials

Doncha just hate those assholes who post the eBay videos shilling their products? I mean, it's nice to get a "live" view of the item you're hoping to snipe at auction, but so many of these tools just plunk the unit down, turn on their cameras and take a movie of the inert item -- not powered up or anything. And usually the movie's too jiggly to do any good anyhow.

Yessir! Ranks up there with the butt wipes who post the blurry photos of their P.O.S. unit and state that they "have no means to test it". Looking at the pictures, however, you can make out a robust test bench in the background with enough equipment to give their auction piece a thorough physical. I translate it as "DOA" and move on.

(Another grind are the guys who market price something at their auction and then try to make up the fees with astronomical shipping charges. Saw a guy selling an off-brand used DMM for $20 -- going rate for the unit -- with a $45 shipping fee.)

Pass-a-Dena.

Well, now that I have groused, I wanted to point out the exception that disproves the rule. Check out the video on a Simpson 260 multimeter below from a seller named BAP8GUY:


Yeah, I know the lighting is not great and the video jiggles, but, I gotta tell you, I'd plunk down the gitas this guy wanted for the unit because (1) I know the unit works and is dead on accurate and (2) the guy told me a whole pile of stuff abut Simpson meters that were cool to know.

If you look at his other videos, you will find out that these aren't the 90 second "spin arounds", some of them being excrutiatingly pedantic; they are almost 30 minutes in length as he steps though the DUT with the machinery on his bench. Apparently, he also refurbs the units and checks them out as well. Here's an HP 1220A:


The only thing about BAP8GUY is that I cannot seem to find him as a seller on eBay. Sure would like to see what he has to offer there; you know the stuff works!

-30-

Thursday, April 2, 2015

It's alive!!!


When I set out on this latest foray into the realm of HP AC voltmeters, my original acquisition was an HP 3400A I got off eBay from a gentleman in North Carolina. It came at a (relatively dirt-cheap price and free shipping and a guarantee. So, it arrived not exactly DOA but not working. I contacted the seller who promptly refunded all of my money and told me to keep the unit.

(By the way, I sent him a check for $25 to cover the shipping; I am not as scurrilous as you might think I am!)

Here is a couple of videos I posted to demo the problem. Clearly, it was not measuring anything.



Anyway, it sat on the shelf for a while and, one Sunday, I saw yet another HP 3400 unit out on eBay for less than dirt. Grandiose visions danced in my head as I picked that one up as a donor. (When will this madness end?)

It arrived, a smoldering hulk (as advertised) and I set about diagnosing the first unit's problems with this as a backup/donor. The adventure was a marvelous exercise in debugging (yet it was not) and a wonderful revelation in how well written the old HP op/tech manuals really were.

(Back again, some time in middle May.)

So, I blocked out a nice Spring Sunday late morning and afternoon to debug this beast, figuring it would take the whole day. What I discovered was that, once you got into it, the HP manuals really are understandable and their troubleshooting steps do make sense. Here are some photos of the guts in no special order, just to give you a sense of that's going on.

Ready to rock..

A4 Board with Thermocouples (TC401 and TC402)

Unit Range Switch

A2 board with Nuvistor

A6 Board Top View

A6 Board Ground Level

To cut this narrative short, troubleshooting involved tracing the signal from the input jack through the range switch, the A2 board and thence over to the A4 board and into the A6 board. The step-by-step guided me past the anticipated shoals of the A2 (nuvistor) and the A4 (with its thermistors) and intact onto the rocky beach of the A6. I was really concerned that the thermocouples had to be replaced but it was not to be.

Anyway, I poked around the A6 board and found that something was misbehaving. Glancing at my donor unit, I noted that its A6 board's photochopper/modulator/demodulator assembly looked entirely different that the DUT and I reasoned that parts swapping was probably not in the cards. After a break for lunch and gazing at the two units, it hit me that both A6 boards, while different, were plug-in units and, in a WTF moment, I swapped them out. (Well, I put the donor unit's A6 into the DUT slot)

Wham!

I fired the sick 3400 up and, after the warm-up mambo, it settled down and behaved like a well puppy! Follow-on measurements and a waltz through the calibration procedures yielded a unit that was shockingly accurate and reliable on all ranges, so much so, that it has now replaced my other 3400 as the official bench AC voltmeter.

What a joyful experience yielding a good unit and three free hours on a Sunday afternoon to play with my new toy and enjoy a couple of cold ones with the bride.

-30-

Thursday, March 26, 2015

Some caveats regarding your HP 403B hunting..


There was one final anomaly to address before this unit was back at 100% and it had to do with the grounding. When I was done, I buttoned everything back up and started testing but, to my alarm, when the unit was plugged in, the measurements dropped to near zero!

I heaved a great sigh, opened up the manual, and started scratching my head. Where to begin?

Then I got some advice form one of the hams who was so helpful before. Simply put, there's two grounds on these beasts. One is the chassis ground and the other is the A2 board ground and they usually should not meet. If you look carefully on the schematic, you will see these grounds represented by little triangles with either a "1" or a "2" in them. Obviously the "1" is the chassis ground -- emanating from the  power line center conductor and the third plug on the front. (See the picture above where the rightmost ground post has a little triangle with a "1" in it.)

Anyway, hooking up an ohm meter to the A2 ground and the ground post on the front panel confirmed they were a continuous circuit. At the risk of a protracted Agatha Christie session, I gotta tell you that the bottom panel has a strip of foam insulation glued over a bump. My anal-retentive tendencies caused me to scrap that off thinking it was some shock padding or something.

Only after flexing the cabinet and the bottom panel and seeing the ground loop make and break, did I realize that the bump was making contact with the interior ground. So, a quick hit with electrical tape and all was right with the world.

A word to the wise, eh?

Final thoughts: Clearly, these are interesting and useful instruments and -- for the money -- a skillful search will yield a clean and worthwhile piece of test equipment. However, I think I lucked out when I got mine. It was clean, in good shape, and only needed one cap replaced and the battery pack rebuilt. The rest was intact and ready to go.

And now here's a dirty little secret: I got a junker off of eBay for spare parts. The price wasn't much; only about $20 or so plus nominal shipping. So, I guess there's about $80 or so into this unit after you figure all of the parts, batteries, and so on. But as W6GVR said, "Never try to justify a hobby."

Still, if you know what you are looking for -- like so many things in this hobby -- you can pick up a bargain learning from others' efforts and mistakes.

I'd counsel for picking up the cleanest unit you can and, if you can, peer inside and see what you are getting. The junker i got was an absolute disaster; all of the little pins and cables had been replaced by some asshole who must have used an arc welder and acid core solder to complete the wiring. So, it you run across one at a swap, bring along a medium sized Phillips head screwdriver and pop the top and bottom panels (only one screw each), slide them out and take a look. Similarly, the two side panels only require the removal of four screws to peek inside.

If the guy won't let you, take a walk; he's hiding something.

Also, assume the battery pack is dead. These are thirty years old and NOTHING lives that long.

Also note that there are two types of plugs: the more conventional type you see with computers and a wired oval one that are found on the units form the 60s and 70s.


If you're getting one of these off eBay and it has one of those plugs (see picture on right, above) and the seller says it does not include the power cord, run like the wind.

I'll put down a few more caveat here as I think of them, but for now, clean and serviceable is usually a good guideline.

-73-

Wednesday, March 25, 2015

Out with the old and in with the new..


After having had a bit of frustration with the shaky needle, I decided to rebuild the battery pack for no other reason than a change of venue, a new adventure, and, what the hell, as my long-ago friend, W6GVR once told me, "Never try to justify a hobby."

Speaking of advice, I received some sterling guidance from yet another ham in Maine, who was in the throes of that awful winter. Herewith is a pretty good description of how the 403B does its stuff:
Howdy Bill--

I watched your flicks! Wow, with the behavior that I witnessed of your 403B it is virtually unusable.

I presume you've got an oscilloscope?

Mine does exactly what yours does on initial power up-- but then settles down and works properly.

On mine switching ranges the needle kicks up a little and then settles down and stabilizes on the reading within about 1/2 second.

I'm working on the house heating system here and that's got full priority-- I've got heat in the house but this is a big job that I'm not enthused about doing this repair but I've got to plod on and get it done.

I want to probe my 403B to watch what goes on at power up -- whether the amplifier(s) oscillate or gyrate at DC levels at initial power up.

I'm also curious what the meter amp does during range switching-- does it oscillate or is it a DC level shift that settles down?

The amp in the 403B may be difficult to probe with the average 'scope unless it's got a 1mV / div vertical sensitivity.

The 403B is designed as a preamp / amplifier or meter driver. It's "native" voltage range is 30 mV full scale-- "straight through". Looks like the preamp has about a 40mV dynamic range. But the meter amp has about a 15 db dynamic range-- or whatever is required to drive the 1ma meter to full scale absolute value. 1 mV into Q3 results in full scale deflection on the meter.

To get to the higher ranges HP engineers have just flanked the preamp (Q1 & Q2) with resistive attenuators. This was done to simplify the input attenuator since it has to work at high resistance. The "secondary" attenuator provides the 1-3-10 scale relation.

The preamp is a bootstrapped emitter follower. The bootstrapping feeds signal in phase from the output back to the input. This makes it look like a much higher resistance input into the preamp since less current drives into the input of the amp.

My schematic shows an 8.2M terminating resistor at the head end into the preamp.

Your meter may vary the resistance as this resistor is selected to provide a termination for the input attenuator and also provide the set meter input resistance. HP chose an emitter follower since they then drive the "intermediate" attenuator which is nothing more than a resistive divider circuit. This way they can use a low "impedance" drive into the attenuator with minimal effect on meter calibration as the user switches through the ranges. This is also done because there is little need for capacitive (or inductive) trimming on the secondary attenuator. The attenuated output from the preamp / input to the meter amp is 1MV full scale (it's probably a tad less than .001V. The emitter follower preamp can not provide any amplification-- it's only function is "impedance" transformation-- HI input to Low output to drive the 'middle' attenuator. You might call the meter driver-- Q3 - Q6 as a voltage to current converter. With .001V input to Q3 the transistor chain will generate 1MA current to drive the meter full scale. To make Q3-Q6 "constant current" a feedback path
across a low value resistor develops. This also linearizes the "steering" diodes especially at low level meter readings (when the needle is just above zero). The voltage drop across the 30 ohm resistor causes the Q3-Q6 network to develop a constant current.

OK-- you say-- so what does all this have to do with the power-up needle dance-- that I dunno yet.

And what about the reading gyrations and the jumps at range selection?

My guess is that the needle fluctuations are because Q1 or Q3 are noisy-- or both are noisy. Q1 is a potential culprit because positive feedback is used and any noise created by Q1 will be exacerbated by the positive feedback from Q2 to Q1.

Another possibility is added resistance by the switch contacts in the "intermediate" attenuator. If you look carefully you'll see that not only is there a voltage divider-- that is tapping "down value" in a resistor chain, but HP has also included series resistors looking into Q3's base. Since the meter amp (Q3-Q6) operate in the 1 mV voltage range (in order to develop 1mA to drive the meter) any added resistance drop will greatly affect the stability of the Q3-Q6 circuit. If the switch contacts are noisy that will also affect the way the meter filter capacitors C17,C18 and the one across the meter behave since those are the "averaging" devices (remember the 403B is only an average reading meter and not true RMS). I think HP recommends cleaning the attenuator switch contacts if the meter jumps around when changing meter ranges.

Kind of the same issue with Q3-- although there's no positive feedback to Q3.

The meter needle not zeroing on the low range-- (.001V) with no signal input and the meter inputs terminated with say a 10K resistor indicates to me that once again Q1 or Q3 is noisy.

You can do a quick test-- by pulling off the "Preamp out" wire (next to the loop gain adj pot). This will still leave Q3's input terminated (not floating)-- see what the meter needle does at any range. Still not zeroing? Switch from the .001V range to the .03V range. Meter zero? If there's no change it points to Q3 being noisy. Another possibility is that C17 and or C18 are leaky. If the transistors are "quiet" they're still going to create some noise level but such that you the observer can not tell that the needle has lifted from zero. But generally the meter will not deflect unless there's an "AC" or better transient signal impressed across C17 and C18. It could be possible that there's a larger than .3V drop across R35. The two diodes are biased almost "on" so that there's no "slack" when an AC signal is present and when the diodes begin to conduct. Although I don't see how this would cause the meter needle to deflect-- unless either of C17 or C18 are leaky.

OK-- I've got to get back to plumbing. I'm sending this as some food for thought.

I have to find some time to experiment with my 403B on this start up needle thing.

73s

Bob
Anyway, back to the battery pack rebuild. You will note, if you do any research on the 403B, that it designed for long-term portable operation and the power supply is nothing more than a charging circuit for the ample batteries that comprise the entire middle compartment. (See the pictures here and in the previous post.) Mine came four tubular batteries -- each 7 VDC when new and charged -- for a total voltage of 28 volts. These are circuited to deliver variously +/-13 volts and 7 volts to the main A2 board. (There is little else but the supply and the A2 board. See Bob's description above.) Of course, like all good things, these batteries are not readily available so some ingenuity is required to concoct a substitute.

Long store short, I cast about on eBay and discovered some NOS cordless cell phone battery packs at 3.6 volts each. Simple math reveals that eight of these will do nicely and there is not a great shoe-horning effort required to stuff them in the case. Be sure you get NiCD batteries and not NiMH. The charger/power supply will fry the NiMH batteries. Here are some pictures of the old batteries and the replacements:








It was an easy matter to join two of the original 3.6 VDC packages into one 7.2 VDC battery as the pictures show. The trick came in wiring them together to get the correct voltages the original batteries supplied but as long as you carefully disassemble the old pack, remember where the purple/black, red, blue, and striped wires hook up, you should be in good shape. I would say my only disappointment is applying the heat gun with too much vigor to set the shrink tube on the battery wires as it caused the yellow binding plastic of a couple of the packs to melt. See the picture above -- it also gives a decent pictorial on how to wire the packs in.


The diagram above is more a depiction of the battery cell hookup in terms of the old style batteries. Below is more of a schematic diagram in the event you use different cells.


By the way, they are nicely held in place by those little two-sided sticky pads from 3M.

Final note on batteries and the 403B: The battery test position of the unit indicates the battery voltage divided by 10. For example, the manual cautions that the batteries need recharging when the meter reads "2.4 volts" which is, of course, 24 volts. In the picture above, my new batteries charge up in excess of 30 volts and, consequently, read off-scale. They do hold a charge as well. The unit fully charges up in the on position and has held a charge for at least a week now sitting on the shelf. (See picture at top of this post.)

Oh, and the great news about this rebuild: the meter needle is rock stable! So it seems that a dead pack was the problem after all!

Next up: the two-ground problem and some meter idiosyncrasies.

-73-