Help needed with 2 resistors, Lafayette FET VOM - Page 1
Forum section: electronics / repair

author: Runco990
author_rank: Frequent Contributor
timestamp: April 07, 2023, 09:33:54 pm
content: So I picked up an "untested" Lafayette FET VOM from the bay.... where else. I have stripped and cleaned it so far, it looks very nice. Meter movement is perfect and it works.However, it has 2 blown resistors. a 2.27Kohm and a 29.5ohm both at 0.5% tolerance, looks like 1/4 watt. I would like to avoid splicing resistors together to make the values, so does anyone have a lead? I have looked and cannot find those values. My "salvaged resistor" box does not have any.It's kind of interesting and I had to rescue it. I do like FET meters to align radios, so I do plan to use it.Original listing pic.

author: alm
author_rank: Super Contributor
timestamp: April 07, 2023, 10:14:52 pm
content: I would just parallel resistors, like 2x59 Ohm for 29.5 Ohm, and 8.06 kOhm in parallel with 3.16 kOhm for 2.27 kOhm. They will fit neatly in the footprint of a single resistor. I know some manufacturers like Edwin Pettis and the Vishay Precision Group lets you order custom values in single quantities, but expect high prices and months long lead times.

author: srb1954
author_rank: Super Contributor
timestamp: April 08, 2023, 02:11:56 am
content: Quote from: Runco990 on April 07, 2023, 09:33:54 pmThose resistors were likely custom made so it is not surprising you can't find them anywhere. The closest standard values are 2.26kand 29.4.However, finding anyone who stocks these or is prepared to supply in small quantities might be frustrating. Using combinations of resistors might be the only option you have.

author: Runco990
author_rank: Frequent Contributor
timestamp: April 08, 2023, 03:31:59 pm
content: Man, you guys aren't kidding. Finding anything IN STOCK is almost impossible these days.Nothing so far on .5% resistors to even cobble something together.

author: alm
author_rank: Super Contributor
timestamp: April 08, 2023, 03:49:46 pm
content: Try looking for 0.1% resistors, they are more common, and in these quantities not that much more expensive. Mouser has59 Ohm 0.5%in stock. I didn't check for the values to make 2.27 kOhm.

author: JeremyC
author_rank: Regular Contributor
timestamp: April 08, 2023, 03:53:13 pm
content: Quote from: Runco990 on April 08, 2023, 03:31:59 pmYou could use the 25 turns, 0.5W trimpots manufactured by Bourns.Don't buy it from ebay, Alix, Amazon, etc. , but from trusted source like Mouser, DigiKey, etc.Check the specs:https://www.mouser.com/datasheet/2/54/3296-776415.pdf

author: Runco990
author_rank: Frequent Contributor
timestamp: April 08, 2023, 04:01:19 pm
content: Quote from: JeremyC on April 08, 2023, 03:53:13 pmThanks! I was starting to think about that. It's not super critical, being an analog meter. I may just do that, even as a temp fix. My primary use is really for peaking, and the handy "0" function. And I just like interesting meters.

author: alm
author_rank: Super Contributor
timestamp: April 08, 2023, 04:48:42 pm
content: Quote from: JeremyC on April 08, 2023, 03:53:13 pmBe sure to put the pot in series with a much larger value fixed resistors, or a series/parallel combination so the pot only represents a small part of the total resistance. Trimpots are not the most stable things, especially under influence of vibration.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: April 09, 2023, 11:20:06 pm
content: Perhaps if you have a bunch of 30 ohm 5% resistors look for one that is 29,5 ohmsLikewise maybe a 2.2 or 2.4 K ohm resistor might be found with a 2.27 ohm value.That is, if you have a good ohmeter that you trust.

author: bdunham7
author_rank: Super Contributor
timestamp: April 09, 2023, 11:44:42 pm
content: Quote from: Runco990 on April 07, 2023, 09:33:54 pmVishay PTF562K2740BYEB (Mouser does not have, you'd have to search)TE Conn YR1B29R4CC (Mouser has)If you can find those they should meet your value and tolerance requirements. If you think they are overstressed and want to go a bit bigger to 1/2W, thenTE Conn H42K26BZA (Mouser purportedly has them arriving in ~90 days)TE Conn H429R4BYA (not in stock anywhere AFAIK, but they might be in the reasonably near future as they are listed as a new product)Additionally, if those can't be procured fast, easy and cheap, you can just get some 1% resistors in some nearby values than then try and select ones that are within your tolerances. It's never easy, right?

author: Runco990
author_rank: Frequent Contributor
timestamp: April 10, 2023, 12:06:42 am
content: Quote from: bdunham7 on April 09, 2023, 11:44:42 pmNope. But I am glad you were able to properly repair that Nixie meter you got from me. I thought it was cool, but I can't keep EVERYTHING!That op-amp was interesting.