Best SGRs?

[tedmich]

is it really best to get as low an inductance as possible on your SGRs in a big bottle PP amplifier?

A lot of people recommend metal film (MF) or metal oxide (MO) resistors in the belief that they are minimally inductive but I've been reading up on their Mfg. techniques and all of these seem to trim their elements with helical tracks and this can cause considerable inductivity. I know wire wounds are quiet and stable but also pretty inductive by dint of their helical wind.

Reading a Vishay spec sheet I see their beautiful NH0051K000FC02 resistor look pretty ideal; 1kOhm 1% tolerance 5-7w
http://www.vishay.com/docs/30201/30201.pdf
and they are have Ayrton-Perry winding, which I think involves antiparallel helical windings with zero net inductance. Ayrton-Perry winding - Wikipedia, the free encyclopedia


granted they are $6 each but that drops to $3.13 if you buy 10...

Would these give me an eargasm in my 5150?

[Enzo]

Why not just shred the $24 and use it for garden mulch? That would eliminate shipping costs.

Screen grid resistors? OK, so what is "considerable inductance"? And please calculate some effect it would thus have on the sound. Note that a popular modification to many tube amps is to replace the resistor with a choke between the plate and screen nodes of B+. A choke being a large inductance. Why would inductance be good there but bad an inch further?

Dose makes the poison, so it is one thing to identify a phenomenon with some attribute of a part, but it is another completely to put it in the context of using the part. An example of that is my mom's car. At speeds in excess of 180 miles per hour, the rear end will tend to gain lift and lose traction. So should I worry? Well, only if mom starts driving at 180 mph or more.

So it is fine to same some resistor has inductance, but how much does it have and what would be the real effect of it in this circuit?

[tedmich]

Shot down by Mr. Sensible again....but isn't a resistor with inductance just offensive?? Like an inductor with capacitance; it make me ANGRY!

And we all know chokes is jokes...but golden SGRs...thats gotta be great!

[Gingertube]

I spent yesterday in the day job trying to trackdown and eliminate noise in a photomultiplier tube based Laser Receiver.
Finally got frustrated enough to pull the 50 Ohm metal film resistor (through which the photomultiplier tube current flows to develop the signal voltage) and replace it with a non-inductive carbon composition resistor.
I was monitoring the result with an expensive Agilent Spectrum Analyser.

So did the change from metal film to a guaranteed non-inductive resistor make a difference?

Yes it did. there was a small reduction in noise starting at about 500 MHz and amounting to almost 3dB by 1 GHz.

Metal Film will be just fine for a Screen Grid Resistior in an Audio Amplifer. If you start to talk about frequencies 10,000 times higher than your audio amplifier then you might consider something else instead.
At audio frequencies it will make a "rodents hind quarters" difference.

Cheers,
Ian

[Leo_Gnardo]

I spent yesterday in the day job trying to trackdown and eliminate noise in a photomultiplier tube based Laser Receiver.
Finally got frustrated enough to pull the 50 Ohm metal film resistor (through which the photomultiplier tube current flows to develop the signal voltage) and replace it with a non-inductive carbon composition resistor.

there was a small reduction in noise starting at about 500 MHz and amounting to almost 3dB by 1 GHz.

Geeze Ian you get all the interesting jobs! Also interesting to note that carbon comp wound up being the choice. As a denizen of Audio Asylum I'm sure you've noted the experts in hi fi usually claim CC is best for grid stoppers too.

[Tone Meister]

... there was a small reduction in noise starting at about 500 MHz and amounting to almost 3dB by 1 GHz...

I heard that!

[tedmich]

I heard that!

golden ears!