[volt-nuts] Wanted wirewound precision resistors and ESI DB877

Fabio Eboli FabioEb at quipo.it
Tue Jun 19 19:35:04 UTC 2012


Hello, as for joining manganin I choose the fast dirty method:
http://tinyurl.com/dxvwy8p

In the 20kohm resistor, I tried to reconnect the broken wire,
I unwound a pair of turns and twisted the two wires together
under the scope. Then I simply brazed them using a little piece
of brazing wire (a speck flattened with hammer)  with a little
borax, more a plumbing work than an electronic one :)

Probably the thermal stress and the contamination isnt good for
a precision resistor, I will replace it anyway, but I will
keep the brazed one just to check it periodically.

Naturally this method involves heating the parts at 500-600°C :)

Fabio.



m k <m1k3k1 at hotmail.com> ha scritto:

>
> Hi Fabio,
> I remembered some problems soldering manganin a while ago, so I  
> googled and this one came  
> up:http://listserv.ipc.org/scripts/wa.exe?A2=technet;a5280f30.1203
> So it is possible not all the previous flux was removed. I thought  
> it was fairly stable, hence a good bet for standard resistors, but  
> if overheated like you suspect then all bets would be off as they say.
> MK
>
>> Date: Tue, 19 Jun 2012 20:04:40 +0200
>> From: FabioEb at quipo.it
>> To: volt-nuts at febo.com
>> Subject: Re: [volt-nuts] Wanted wirewound precision resistors and ESI DB877
>>
>> Here I put some photos of the decade:
>> http://www.eevblog.com/forum/product-reviews-photos-and-discussion/db877-teardown/
>>
>> Frank Stellmach <frank.stellmach at freenet.de> ha scritto:
>> > I think, you should better measure the resistance by a high
>> > resolution DMM, on its normal OHM range.
>> > Thats much more stable and less power is dissipated. A comparison
>> > between two of them is also much easier.
>>
>> Yes I'm using a pair of multimeters: the keithley 2015 and
>> a solartron 7061, the keithley should be not far from real
>> values, but has a maximum count of 1200000, the
>> solartron is "zeroed" against the keithley,
>> has a maximum count of 21000000, permitting to compare
>> the 1M and 2M resistors without changing range and resolution.
>>
>> I used the fluke to try to test for leackage, I
>> tought that if there was some leackage, the current
>> would have been higher than V/R ratio and not
>> proportional to the voltage.
>>
>> > ingresses between the windings. I assume, your resistors are tubular
>> > ones, with plastiv caps around, and they are not hermetically tight,
>> > therefore they cant be filled completely for corrosion protection
>> > and thermal  conductivity, like in the Vishay metal foil VHP type.
>>
>> See the link, there is a pic of the resistor, it's open, no protection
>> at all.
>>
>> >
>> > Besides electrical measurement (on OHM range!), I 'd recommen
>> > optical inspection of the case, and if its possible, of the windings
>> > for burnt/overheated areas. Corrosion may be easily identified, also
>> > by slightly stained parts of the wire.
>>
>> yes, the low valued resistors (10/20 ohm) seem a little corroded.
>> The intermediate valued ones seem ok.
>>
>> Is the wire used (manganin?) prone to corrosion?
>>
>> Fabio.
>>
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