Tracking resistors

You are pushing your luck. Use some 6 cent Susumu thinfilms, which are spec'd at 25 PPM but are typically more like 6. One of those should drop into a melf footprint.

You can buy 25ppm thin films on the E192 grid - and as John Larkin says - they aren't all that expensive, and a lot less expensive than making a three element substitute.

It you want stuff to track you can buy thin film arrays on a common substrate - never with the exact resistance you want, but you can frequently get close enough.

Thanks, 25ppm are indeed easy to get - did not think they were... Film array won't work, resistors of the same value - even 50 ppm - when bought at once track very well anyway, I am after different values which track. Most of those mini-melf we use do track well (well, those I know of), but some don't. E.g. the 2k and 1k - bought at the same time IIRC, 1000 each I think it was - don't track well at all. I expect buying 25ppm instead of 50 will make things better, will try.

Had not seen your message earlier (got up early, sleepy all day), thanks! Will look for those susumo resistors.

I believe it was Susumo that made a part we used because it was unique in terms of power density. Then they stopped making it or at least everyone we bought from stopped selling it. We had to scramble to find a replacement. Fortunately in the intervening time another company or two started making a competitive product.