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 Post subject: Meter "Repeatability" Question
PostPosted: Nov Tue 30, 2004 11:19 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2478
Location: Malone, New York USA
Hi-<P> OK, so I repaired the meter in my recent acquisition. Hickok 533"A"<P> Merely the coiled balance spring rubbing on the pointer counterweight at 0-30% of scale.<BR> <BR> Coil tilted to one side from someone slapping the meter to make it work...most likely static build-up being the initial culprit...outer end of coil spring bent at point of attachment to indexing arm.<P> My question:<P> When testing the meter's movement, I notice the pointer may/ may not land _exactly_ at the same spot at rest, depending on the amount of deflection.<BR> <BR> For instance:<BR> Properly zeroed out. Pressing P7 and set to line adjust.--Release, and it drops- lightly bounces off mechanical stop (scale undershoot,) and rests _exactly_ over the centers of zeros. Repeats exactly every time... from the same amount of deflection.<BR> <BR> --Barely "bumping" P7 to maybe 5-10% of full scale deflection and it may/may not return to _exactly_ center of zeros.<BR>--Within the zeros, but not _exactly_ centered..paralallax being considered...<BR> I've never noticed this on the non-"A" models of Hickok testers I've had or have now, or any other _quality_ meter movements before.(i.e. Simpson 260)<P> No particles/ no binding/ touching of balance spring turns.<BR> Pivot adjustments haven't been played with.<P> Am I just being "anal" and "chasing my tail" regarding this, or could there be a tiny bit of excess friction at the pivot points?<BR> No _visible_ corrosion observed.<BR> This tester shows it wasn't used very much.<BR> <BR> I'm hesitant to apply _any_ form of lubricant to the pivots on just a guess, and I'm hesitant to loosen pivot bearing adjustment, since the meter does show ease of movement. <BR> Various readings remain the same across the scale.<BR> (Power applied)<P> Pointer balance is good--stabile either vertically or horizontally. <P> The only adjustment I made to the meter was the magnetic shunt...Meter was reading 3/16" high off-scale with 500 microamps applied (Read w/ Fluke 83) Shunt now near one end of adjustment slot.<P> -Just a phenomenom of this particular style of meter used in Hickoks, or a (very slight) problem here with this particular one?<P> I'd be interested to know if the <BR>all-plastic meters on other "A" models or newer models exhibit this sort of non- repeatability.<P> Thinking the amount of (percent of full scale) deflection and pointer inertia _might_ play a part?<P> I can't call this "my tester" 'til I find an answer.<P> Thanks,<BR> Den<BR> <P>------------------<BR>


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 Post subject: Meter "Repeatability" Question
PostPosted: Nov Tue 30, 2004 3:39 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 828
Location: Grand Blanc, MI USA
I have seen this sort of thing many times, and believe it is due to slight additional friction at the pivots. Sometimes this can be improved by cycling the meter with a function generator, at say one cycle per second--for an hour or so. This can help "polish" the pivots and bearings. It does not work every time--maybe 50%. It takes a series resistor and careful adjustment of the DC offset to get the meter cycling properly.<P>If the meter zero is the only problem, I'd say that is a non-problem. This is because the meter on a 533A is never asked to take a measurement at zero. The main thing is that the meter read the same every time when a given current is applied--since this is what determines its accuracy in testing tubes. Usually meters that stick at zero, are a bit sticky at other parts of the range. Sometimes a gentle tap next to the meter will be the most effective way to get the most accurate reading.<P>Some meter designs just seem to be more friction prone than others. I have found the Hickok model 752 meters (older type in black case) to be the most damped and sticky. Virtually every one requires a slight tap to get maximum accuracy. Many TV10s also seem this way. I suspect that these meters were on the verge of sticking the day they were made, and 40 years later, that's just the way they are.<P>It makes you really appreciate taut band movements.<P>------------------<BR>


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 Post subject: Meter "Repeatability" Question
PostPosted: Nov Tue 30, 2004 7:40 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 31285
Location: Maryland 20709, USA
Hi All,<P>Meters of this quality should never "stick". They should repeat within the width of the needle for a given applied current, assuming the current is accurately controlled. Non-linearities and scale accuracy are not related to the sticking problem.<P>Static on the meter face could cause this. But since you mentioned that in your initial post, I assume you eliminated that possibility already.<P>My guess would be dirt buildup in the pivots. Try backing one pivot screw out about an eighth of a turn, while holding the jam nut in position. Then try the test again.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR><A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A> | | <A HREF="http://www.Synchrophase.info" TARGET=_blank>http://www.Synchrophase.info</A>


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 Post subject: Meter "Repeatability" Question
PostPosted: Nov Tue 30, 2004 9:02 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2478
Location: Malone, New York USA
Hi Chris-<P> Thank you very much for the insight from a much broader perspective/ knowledge base regarding these things.<P> Makes me feel a bit more confident about that tester, before I trade off the non-"A" 533 here. (Can't see keeping both 533s, with a 600 available.)<P> The function generator cycling is a great idea...<P> I had thought of repeat cycling, but repeatedly pressing the P7 button didn't seem the way to go... <IMG SRC="http://antiqueradios.com/forums/smile.gif"><P> I don't have a function generator here, but I do have a couple of Omron "repeat cycle" timers that are very flexible with on/off times and intervals settings.<BR> Should "do the trick" nicely.<BR> I'll be sure to adjust the cycling to keep the pointer from returning/ bouncing off the low end stop... or "pegging" high end- (keeping pointer on-scale) <P>I wouldn't want to screw that meter up at this stage of the game...<P> I'm going to (hopefully) locate R24 (25K)resistor and "tweak" it to get all voltages just a tad lower (closer to spec) in relation to line set adjustment.<P> AC and DC voltages are very close to spec,<BR> most within +/- ranges but all just a little high after adjusting full-scale range for the meter.<P> Before meter shunt adjustment, all voltages were just a tad lower than published specs..<BR>except for the screen and bias resistor adjustments -- they were a bit high as-found...<BR>Not uncommon, I've observed, for these two voltages to have have drifted in as-found units.<BR> Both were found to be just out of spec range (high,) and are now proportionally higher along with the other voltage readings. <BR> <BR> The R24 tweak _should_ fix that...according to Hickok's Mr. C. Lenko...<P> Thanks again!<P> Den<P> P.S.- This tester calibrating stuff is interesting, but I personally wouldn't want to make a hobby or business out of it.<P> I'd rather have one decent compact 600"A" companion to the 600 here, but current on-line prices for the 600 series rules that out for me, so I'll be satisfied with the 533A.<BR> What I regard as next-to-junk 600 series units, untested or with major issues sell for astounding (to me, anyway,) prices! <P>------------------<BR>


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 Post subject: Meter "Repeatability" Question
PostPosted: Nov Tue 30, 2004 9:22 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2478
Location: Malone, New York USA
Hi Leigh,<P> The meter in question performs well (repeatable,) while under power (readout mode,) it is just the "zero" center (return) that is a "hair" variable,(within the printed "zeros.") <BR> This is solely dependent on percent/ amount of powered deflection up-scale.<BR> <BR> Yes, the thought of pivot adjustment entered my mind, but I feel confident thus far that it is OK.<BR> <BR> If it is microscopic bearing/ pin surface roughness due to lack of use (as evidenced by the tester's overall condition,) -loosening the pivot clearances may not improve things.<BR> Armature would still be resting on a bearing surface with a certain coefficient of friction. <BR> I'll opt for the cycling (self-burnishing) session first, then see what happens..<P> As mentioned, I'm not talking gross variable error here..<P> Den <P>------------------<BR>


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 Post subject: Meter "Repeatability" Question
PostPosted: Nov Tue 30, 2004 10:00 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 410
Location: Tokyo, Japan (2006~)
Hi Den;<P>Just in case... before you decide to throw your 533A against your backyard cement porch (I mean for any reason <IMG SRC="http://img.photobucket.com/albums/v297/angusx/wink.gif"> at all) be sure to throw it this way. I'll make sure to provide a nice home for it and promise to never eBay it...<P>------------------<BR>Chris M.<BR>Windy City USA


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 Post subject: Meter "Repeatability" Question
PostPosted: Nov Tue 30, 2004 10:29 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2478
Location: Malone, New York USA
Sorry, Chris M., but throwing stuff from frustration (if I ever do develop any with this hobby,) is not my style...<BR> I was born before "instant gratification" became buzz-words.<BR> Actually, if I weren't so fussy with this one, I'd complete the calibration procedure and accept it as it is.<BR> Just too fussy for my own good, sometimes..<P> Non-frustrated Den<P>------------------<BR>


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 Post subject: Meter "Repeatability" Question
PostPosted: Dec Wed 01, 2004 8:14 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1413
Location: Qu├ębec!
Old Radioz wrote:
<font>quote:</font><HR>Originally posted by TurboServo:<BR><B>Hi Den;<P>Just in case... before you decide to throw your 533A against your backyard cement porch </B><HR>
<P>As Den says, you will _never_ see him frustrated. This guy is patience and perfection incarnated. He could spend a whole day taking apart and re-assembling a tiny meter movement without a hint of frustration until it is perfect. 8^o<P>Syl<P>------------------<BR>


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 Post subject: Meter "Repeatability" Question
PostPosted: Dec Wed 01, 2004 9:44 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 410
Location: Tokyo, Japan (2006~)
Hi guys;<P>Auuuuh, I thought so too, but I had to offer...<P>------------------<BR>Chris M.<BR>Windy City USA


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 Post subject: Meter "Repeatability" Question
PostPosted: Dec Fri 03, 2004 11:05 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2478
Location: Malone, New York USA
Chris H.<P> Thanks once more for the meter self-burnishing cycling tip...<BR> Hooked up the repeat cycle timer...just the thing for this.<BR> Tick-tock-tick-tock...one hour later, the repeatability at zero is.....zero!<BR> Must've been lack of use and sittin' around for years.<P> Now, tweaking the R24 (in line adjust circuit) - 215K was 3K high as found, to center the voltages with line adjust.<BR> Critical tolerance with that one!<BR> Circuit on this example wants the precise published spec of 215K to bring all the fixed voltages towards spec. center.<BR> Learned sumthin' else with these 533As.<BR> Learning is good!<P> Den<P>------------------<BR>


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 Post subject: Meter "Repeatability" Question
PostPosted: Dec Sat 04, 2004 12:55 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 871
Location: Wa
Although you seemed to have a solution, one tip is if you have any meter that maybe effected by static electricty on the glass or plastic. Clean it using only dishsoap. then dilute some clean dish soap in distilled water and use a pump spray bottle with mixure. Let dry before assembly. That should take care of static on the lens.<P>------------------<BR>The light of one candle can extingush all the power of darkness (evil)


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 Post subject: Meter "Repeatability" Question
PostPosted: Dec Sat 04, 2004 9:52 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2478
Location: Malone, New York USA
Hi Cliff-<P> Yes, thanks, I'm aware of the propensity of these meters to collect static charges.<BR> I have bottle of anti-static spray made for the purpose that I use.<BR> You bet- dishwashing detergent works well too, as you suggested.<P> Den<P>------------------<BR>


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