[volt-nuts] Fluke 720a self calibration repair

[Dave M]

Rob
Thanks for the offer.  I received an offer of a (nearly) complete unit from 
another list member.  If that turns out well, I should have all the spares 
that I'll ever need.

If it doesn't work out, I'll surely be back in touch with you.

Dave M



Rob Klein wrote:
> Dave,
>
> How many of those pots do you need? I've had the innards of an
> 88(something) lying around for ages and your welcome to a few, if
> you're willing to pay shipping from the Netherlands. With only the
> trimmers in a small box, that should not break the bank.
>
>
> Met vriendelijke groet,
> Rob Klein.
>
> Verstuurd vanaf mijn tablet
>
> Dave M <dgminala at mediacombb.net>schreef:
>
>> I tried to find this style trimmer pot with a wirewound resistance
>> element, but found that all I could find was the Cermet type.  It
>> appears that wirewound pots have all been replaced by Cermet. the
>> wirewound pots had a 1W power rating, whereas the Cermet pots arte
>> only rated at 3/4W.  In the 720A, the reduced power rating won't be
>> an issue, but in some vintage equipment, it might be.
>>
>> I've also tried, to no avail, to find a source for the metal-cased
>> wirewound trimmer pots used on the K-V divider in some older Fluke
>> differential voltmeters, such as the models 883A, 885A and 887A.
>> Does anyone know of a source for replacements for those pots?   I
>> have an 887A on the shelf that I'd like to get back to original
>> condition if I could find a couple of that style trimmer pot.
>> They're only 2 ohms, making the search even more difficult.  At this
>> point, my only recourse is to find a defunct donor unit at
>> reasonable cost, and salvage the parts. Does anyone have a hangar
>> queen that I could get for shipping charges?  I'd be really happy to
>> get mine back on the road to health.
>>
>> Cheers,
>> Dave M
>>
>> Tony wrote:
>>> Apologies - my mistake - I wasn't paying sufficient attention when
>>> Google decided that this was a perfect match when searching for
>>> 300SP-1-502:
>>> http://uk.farnell.com/webapp/wcs/stores/servlet/Search?st=3400s&catalogId=15001&categoryId=700000005471&langId=44&storeId=10151
>>>
>>> But £180.27 each whereas Newark, the US arm of Farnell only want
>>> $120 or approx £80 for the same part! Are there really that many
>>> Brits who put up with being ripped-off to these levels?
>>>
>>> Tony H
>>>
>>>
>>> On 26/09/2015 01:27, Charles Steinmetz wrote:
>>>> Charles wrote:
>>>>
>>>>>> I had to look it up. The company was Arrow (800 833 3557). The
>>>>>> pots were manufactured by Bournes with a manufacturer part
>>>>>> number of 300SP-1-502. Unit cost $7.73 in 2011. I bought 26 so
>>>>>> my cost was about $200. I wanted a "Manufactured in America"
>>>>>> part but can't remember if that was too pricey or not.
>>>>
>>>> Tony wrote:
>>>>
>>>>> They are now $92.55 from Arrow now and Farnell want over $200 each
>>>>> if you buy 25 or more!!!! There don't seem to be any obvious cheap
>>>>> alternatives for 10 turn 20ppm/C 5W pots.
>>>>
>>>> The original pots were Bunker Ramo-Eltra (later, Bunker
>>>> Ramo-Amphenol) P/N 3800P-502.  These were 20-turn, 5k, 10%, 1W,
>>>> +/-50 ppm/C wirewound parts in the 34b rectangular package.  The
>>>> Bourns 3005P-1-502 matches these specifications (I suspect "300SP"
>>>> in Charles's message was a typo).  I do not know if the pin layout
>>>> is the same as the 3800P-502. Verical has the lowest price on the
>>>> 3005P-1-502 that I could find in a quick search, $7.68 each. Others
>>>> charge from $9 to $14. Tony -- what part number were you quoting
>>>> specs and prices for?  I
>>>> found nothing searching for "300SP-1-502."
>>>>
>>>> Best regards,
>>>>
>>>> Charles