BIAS SUPPLY RESISTOR RATING

[ViperDoc]

I wondered what the sages would recommend regarding bias supply resistor power ratings? Such as voltage drop resistors in the bias supply and resistors to ground. I've tended to use what's on hand, which likely involves overrated resistors, even 3W. I'm sure it doesn't hurt, but I was just curious. Many thanks.

[TUBEDUDE]

Low current, low voltage, low power 1/4 watt will do, but I use 3W everywhere.

[Ten Over]

I wondered what the sages would recommend regarding bias supply resistor power ratings? Such as voltage drop resistors in the bias supply and resistors to ground. I've tended to use what's on hand, which likely involves overrated resistors, even 3W. I'm sure it doesn't hurt, but I was just curious. Many thanks.

The sages would surely need to know exactly what bias circuit you were talking about.

[sluckey]

You could browse through some schematic libraries and find out what the original sages used. You might even find some other interesting facts too.

[ViperDoc]

You could browse through some schematic libraries and find out what the original sages used. You might even find some other interesting facts too.

Fair enough, that's good advice. Just like in all the schemos I've seen, I've noticed differences in many builds presented here, too, so I wondered about the rationale behind it.

[Stevem]

Since the bias voltage needs to be quite stable and these circuits always seem to be in the hottest areas of the amps near the output tubes, at least the AC dropping resistor before the diode( s) I up rate by 100% from whatever wattage it is stock , or if your building something then the added cost of even a 3 watt 1% resistor is nothing!

[TUBEDUDE]

I use 3W resistors everywhere I don't use wirewounds (the power string and tube screens). I recommend 3 Watt MF everywhere, unless it's being used it in a fuse function, or if a specific sonic goal depends on a low wattage carbon comp.
3 watts are quieter than their lower wattage brethren, and I'll bet more thermally stable also, likely due to larger mass. It makes little extra cost in an amp (excepting large scale mfrg.), makes less line items to stock, and easier ordering. Works for me anyway.

[Stevem]

The noise factor does not come into play in the bias circuit!

[TUBEDUDE]

No, it doesn't. Doesn't hurt either. My point is I stock one part at that value and use it freely anywhere.

[sluckey]

I recommend 3 Watt MF everywhere

I've never seen a 3 watt MF. Doesn't mean they are not out there. Are you possibly talking about metal oxide?

[TUBEDUDE]

No, metal film. I mostly use GS3, but several mfgrs. make a 3W.

20211120_214309.jpg

Here's a few assorted 2 and 3 Watters.

20211120_221317.jpg

[Murrayatuptown]

Good idea.

Good power rating, voltage limit and TCR. Kill three birds at once.

https://static6.arrow.com/aropdfconvers ... asheet.pdf
TT/IRC GS-3

Arrow calls them obsolete, so probably not a good source. Mouser had slim offerings under a search for just TT.

Broadened my search for metal film 2-3W, +/- 100-200 PPM
https://www.mouser.com/c/passive-compon ... oefficient
& there were a lot of offerings. I didn't like the pricing on all of them.

[Stevem]

I use 3 watt MF in preamp plate load sections and there not even as big as a 1 watt carbon resistor.