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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Mar Thu 27, 2003 4:32 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 446
Location: Winnipeg, Manitoba, CANADA
Well, not disect it, really. I have a 157 with a blown meter coil. No big deal, the tester is awful, anyway. However, the more I play with all of my gear that isn't working, the more excited I get. So, now I have the meter coil apart, and have started rewinding it. If anyone know what the full scale deflection current is, or wants to find out the DC resistance of the coil itself, I would be forever indebted to that person. I have the plan now just to wind away, and if it 'works', great. By using tubes that I kinda know the emission reading of on any other tester, I can 'calibrate' this thing with a meter shunt. Not worth the time, really, but I kinds like doing silly things.<BR>Anyway, thanks for any advice/assistance. <P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Mar Thu 27, 2003 8:02 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3667
Location: Circleville, OH, USA
I have the greatest admiration for anyone who would undertake to rewind a meter. Let us know how it goes.<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Mar Thu 27, 2003 9:15 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
Just a SWAG, Accurate probably used the cheapest possible meter, which would likely be 1 mA F.S.<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Mar Fri 28, 2003 3:26 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 795
Location: Gulf Breeze, FL USA
WOW! I'm with Ken, how would you even go about rewinding the coil? I've been beating my head against the wall for about 3 weeks over a TO-6 with a bad meter. I'd be very interested in how you are performing this<BR>task. Where do you get the wire, how do you see what the heck you're doing etc.<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Mar Fri 28, 2003 3:47 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 446
Location: Winnipeg, Manitoba, CANADA
The funny thing is, if you look at any advertising for the Accurate 157 (like in Mr. Douglas' book), they claim to use a 'rugged, accurate, highly damped meter movement with SEALED air-damping chamber'. Sure. It came apart just at the sight of my Xacto knife. The coil looks real cheezy, too. Kinda like a spool of thread; the cheap plastic bobbin actually came apart as I unwound the 'old' coil. The bobbin is just glued roughly centered around the back of the needle/magnet 'assembly'. Cheap. Any other coil, and I wouldn't even try. But I bought a 5-pound spool of 42 gauge magnet wire, so I had better start justifying the purchase. I made a little hand winder (although eBay even has a handful of books/plans for winding 'machines' that look more sophisticated), and just go slowly, because if I tense up a little too much... SNAP! So, I have started two or three times, and after 15 minutes or so I must just feel like breaking this piece of human hair they call magnet wire. I'll have it soon. I only go to the 'shack' on weekends, so it'll no doubt still be there Saturday. <BR>I need a better hobby, I know. I tried drinking, but no one who comes over the house comments on my collection of 'empties'.<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Mar Fri 28, 2003 6:48 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 477
Location: NC
Randy<P>If your Accurate 157 had a line test function, you should be able to guage the meter ma rating by performing the line test and using another milliamp meter to measure the reading. If the line test mark were at the center of the meter, chances are the reading would be @ 1/2 the full swing ma reading (if the line test adjustment pot were centered).<P><P>------------------<BR>Ken


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Mar Fri 28, 2003 5:50 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 596
Location: Buckingham County, VA. (Foothills of the Blue Ridge Mtns)
Seems to me that trying to rewind a meter coil is gonna drive you back to drinking .. but I do applaud your effort.<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Mar Fri 28, 2003 9:17 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
No. 42 sounds heavy for a meter coil, though it's perfect for interstage audio trannies or headphone coils. I've never tried, or even thought about trying, to rewind a coil, though I have resoldered a broken meter coil once, in my Hickok/W.E. KS 15750 tube tester. I once rewound an interstage with #46 but that was unnecessarily fine. I have some #47 but never found any occasion to use it.<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Mar Sat 29, 2003 8:02 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3162
Location: Cockatoo, Victoria, Australia
Hi Maschocist Randy, If your coil of wire has smooth, rounded end cheeks, stand it upright and let the wire unravel off the end. That will overcome the reel inertia as it unwinds and should reduce wire breakage. If you get the sensitivity close you should be able to calibrate it by moving the magnetic shunt across the gap. It's usually held by a single screw and can slide back and forth across the gap to trim the magnetism.<BR>Are you looking for a meter that's advertised as " a terrible piece of junk but buy it anyway - I need the money"? Seems everyone thinks their product is the best ever made; and they should know, shouldn't they. would he lie?<BR>Don Black.<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Apr Sat 05, 2003 3:12 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 446
Location: Winnipeg, Manitoba, CANADA
Well, this is a learning experience, to be sure. The 42ga. is so thin (like a politician's promise), it likes to break at the most inopportune time. I realize you need tension, or you'd just get a few loose wraps. I had it completely wound once, but buggered it up trying to solder it to the meter movement 'posts'. Aargh!<BR>Anyway, because I had some 30ga. that I 'forgot' I had, I wound it up again. Very easy this time; much less prone to breakage. However, the FSD isn't near where I would need; no tube would read higher than 20%. So, I checked a few motor rewind shops; 34ga. is next. I have the roll sitting next to me, and will keep anyone who gives a hoot abreast of any development. FYI; the resistance if the 42ga., even though it never made it to the final stage, was 1800-ohms. The 30ga. coil I can't remember(!), but I think it isn't gonna work; it 'saturates' pretty quick. I cannot get more than 1/2 scale deflection with a bias box that goes up to 30VDC! Anything past about 15VDC doesn't produce anymore deflection. I'll have to read my old college books and see what is up with that.<BR>Anyway, that's it. It's pretty easy to rewind the meter movement coil, if you use heavier wire. As the gauge gets higher, so does the frustration level. I'll find a compromise, and have the satisfaction of conquering this thing yet. So what if I paid $20 for this cheesy tester, and another $20 for wire? And who needs a healthy liver, anyway?<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Apr Sun 06, 2003 6:37 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 446
Location: Winnipeg, Manitoba, CANADA
OK; here's the latest. With 30ga. wire, the DC resistance was 20-ohms, and the FS was about 200mA. Not good; no tube read more than '20' on the meter. So, 34 ga. wire next. The DC resistance bumped up to 70-ohms, and FS came down to about 100mA. Most tubes registered about '40' or a little better on the meter. I'll keep trying anything other than human hair, or 42ga. wire, and see what transpires. <BR>The more I play, the more I learn. The biggest thing I learned was how the idea of spending time on it is baffling. I tried measuring current with a tube under test, and a 6K6 ran 18mA. A 12AU7 didn't run much less; about 15mA! Lowering the 470-ohm resistor in series with the tube under test didn't make too much difference. I could run 6K6's up to 25mA, and the meter read as high as '60', which isn't too bad I think. But, 12AU7's ran about 17mA or 18mA, and I'm sure that's bad.<BR>Well, that's how I spent my Saturday. It was either that, or watch Hockey on TV while I nursed a beer. I think I chose wisely. I'll compare test currents of any Eico or Heathkit I have, and if they run 12AU7's that high, I'm close to done. I'll lower that 470-ohm resistor, and be done with it. That's it. <P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Apr Wed 09, 2003 2:03 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 795
Location: Gulf Breeze, FL USA
Hi Randy,<BR>Since you now seem to be the resident expert on magnet wire, maybe you can answer a question of mine, ie. what is the resistance in ohms per foot, furlong, or fortnight (snicker) of the various gauges of wire?<BR>I need to wind an 8.7 ohm resistor on a small bobbin and wonder what gauge to use. Thanks, Ben Gray <P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Apr Thu 10, 2003 3:05 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 446
Location: Winnipeg, Manitoba, CANADA
Well, I ain't no expert, but I love to experiment. I have a few friends up here that are real 'old timers' when it comes to tube electronics, and I hang around them as much as I can. My 'favorite' person to pick on is an octogenarian that actually was an engineer at Philips over in Holland during the development of the ECC83! Anyway, he always chides me when I ask him for a power transformer with a 5VAC winding. He'll say we 'kids' have it good, where we can buy Hammonds pretty easy. He would tell me to add a 5-volt winding to a transformer I already have, and then show me how to do it, complete with a lesson in the math. He's responsible for getting me into doing things and getting my hands dirty.<BR>Anyway, that's not important right now (or anytime that I can think of). You need an 8.7-ohm resistor. I dug out my old college books (1979!) and my charts only go to 40ga., so here is some common numbers. 40ga has a CSA of 9.89cm and a resistance per 1000 feet of 1049-ohms. Down at 30ga, we get 100.50cm of cross-sectional area, and 103.2-ohms of resistance per 1000 feet. 34ga. has a CSA of 39.75cm and 1000 feet has 260.9-ohms of resistance. 38 ga. has a CSA of 15.72cm, and 659.6-ohms of resistance per 1000 feet.<BR>I do a lot of magnetic experiments with my kids for school projects. We always do well at science fairs with little projects I find in old magazines. The 'neatest' one yet was a very crude speaker! It worked, sounded horrible, but got my daughter an 'A'. One website that helps when we need to wind chokes or coils is over at <A HREF="http://www.vwlowen.demon.co.uk/java/coil.htm," TARGET=_blank>http://www.vwlowen.demon.co.uk/java/coil.htm,</A> and it is pretty neat. It works out inductance for you. You need a small resistance, so for 8.7-ohms, I'd first try 134 feet of 28ga. wire. It works out pretty close. According to my chart, it has a CSA of 159.79cm, and 1000 feet give 64.9-ohms of resistance. I don't know the size of your coil form, but that can't be too bad; easy to handle, and easy to solder to. If you have 30ga. wire (or a small form), the math works out to about 84.5 feet. After 34 ga. wire I have a hard time handling it and soldering it. Oops; use 13 feet, 2 inches for 34 gauge.<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Apr Thu 10, 2003 8:24 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
You need resistance wire, as you'll never get enough copper wire on the bobbin.<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Apr Fri 11, 2003 5:02 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 795
Location: Gulf Breeze, FL USA
Thanks Randy for the great answer and the research required to get it. I unwound the old resistor and found only about 3 feet of cloth insulated wire, so it looks like Alan is right. I've ordered some 28 gauge nichrome wire from AES that's supposed to be for wirewound resistors, but it doesn't look like its insulated. Anyone know how to use this wire for winding a resistor?<BR>Thanks again, Ben <P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Apr Fri 11, 2003 8:26 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
Can you re-use the old wire? Often the solder joints corrode at the ends, but the wire itself is ok. If not, I guess you need resistance wire of about 3 ohms per foot. I have some if you get stuck, in various gauges.<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Apr Mon 14, 2003 4:50 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 795
Location: Gulf Breeze, FL USA
Thanks Alan.<BR>The cloth insulation came off the wire during the unwrapping operation and the wire broke a couple of times, its shot. I'm going to try dipping the 28ga nichrome in Plas-Ti-Dip to insulate it and then wind the new resistor with it. If that fails, I'll take you up on your generous offer.<BR>Best Regards, Ben Gray <P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Apr Mon 14, 2003 8:15 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
I doubt if the dip will work, as it is soft and will flow under pressure. I found some #28 resistance wire of about 1.5 ohms per foot; the only 3 ohms per foot I have is #40. Most of my stock is higher resistance.<P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Apr Tue 15, 2003 2:50 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 446
Location: Winnipeg, Manitoba, CANADA
I don't ensorse eBay, unless you are a seller, but a fellow did have a small selection for auction. He offered 22ga., 24 ga., 26 ga., 28 ga., 30 ga., 34 ga., and 40 ga. all in very small spools. He'll probably be back. 40 ga. has a resistance of 70-ohms per foot, so that's waaaaay too fine. Right now you can buy 25 feet of 25 ga. at this auction; <A HREF="http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2523430412&category=26261." TARGET=_blank>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2523430412&category=26261.</A> He'll throw in the shipping for $6.51, so the price ain't bad. I have in my chart 24 ga. with a resistance of 1.671 ohms per foot, or 26 ga. with 2.67 ohms per foot. I think 25 ga. would work, and you have to have enough room on a bobbin to wind four feet of nichrome wire. <BR>I must have a different chart, unless they make different types resistance wire; I have 28 ga. having 4.251 ohms per foot of resistance. <P>------------------<BR>


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 Post subject: Anyone want to disect an Accurate 157 meter?
PostPosted: Apr Tue 15, 2003 4:33 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
Oh yes, there are a gazillion different alloys. The particular #28 I mentioned is Cupron copper-nickel alloy by the Wilbur B. Driver Co., double nylon covered, 1.8 ohms per foot, dated 1945. I have no idea what that alloy was made for. But I can send a few feet in a first-class envelope, for the cost of postage.<P>------------------<BR>


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