Re: Resistor in series
Hi Jeff,toggle quoted messageShow quoted text
You are correct that, depending on value, metal film resistors can have significant inductance (relative to the carbon comp version). In this particular circuit, though, you are looking at 7.5 kilohms of resistance in series with a negligible inductive reactance (I'd guess an inductance well below 100nH, so an inductive reactance of tens of ohms or so at the top end of the scope's bandwidth). So here, the choice is driven by power and capacitance (and maybe aesthetics). Inductance of the resistor is totally irrelevant.
I confess to a general prejudice against carbon comps (they're horribly noisy under bias and don't age gracefully), but they will work here, of course. Just pre-measure the resistance before installation. You might find that even NOS resistors have drifted significantly upward in value just sitting on a shelf.
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford, CA 94305-4070
On 11/25/2020 20:09, Jeff Dutky wrote:
So I feel like a superstitious/nostalgic idiot, but I had second thoughts about replacing the out-of-spec resistor pair with modern metal film resistors. I went to eBay and bought a dozen (allegedly) genuine Allen Bradley carbon composition 7.5 K Ohm 1/2 Watt resistors for what is probably a completely unjustifiable price. I also looked to see if anyone was selling FDH2161 diodes, but no luck on that score.