May be I missed it... After long hours of listening my color preamp starts making a high pitched noise. So, I'm 57 and use high pitched noise with a grain of salt. Thing is its not coming through the speakers. Wiggling tubes does not do it, didn't try swapping yet as something popped up while I was poking around. I started thinking the only difference between a cool amp and one that's been on for a good long while is heat... Having access to a professional flir thermal imaging camera (at least 15 years ago!) I discovered R1 in the PS at over 177 degrees! A few quick measurements later it's 1.99k dropping 24v
.... 24/1990=12mA ... 0.012 x 24 = 0.288 w
For a 2w resistor a hair over 1/4w should be no big deal right?
Kinda feeling like regardless of the ratings, 177F is too damn hot.. didn't have any 4k 2w resistors to put in parrallel so made up my own 4 resistor (each 2k 2w) bank and wound up with 1975 ohms (close enough)
Surprisingly they run around at 140F Which is just barley too hot in my book way better than 177f. Anyone ever do a heat analysis on the temperature curves on resistors as amps rise?
I'm surprised the 177deg f just didn't divide by 4???
Anyways I don't know if it's fixed stay tuned...
Looking into this further, I see the Vishay datasheet max hot spot temp is 250C!! Im certain this is a non intuitive statement, but even less than half of that say 100C is 212F, so appears WELL within the working parameters. That said, I don't like it one bit lol.
Id imaging a 10w wire wound ceramic would run at a lower body temp....
Any reason why a that might be a bad choice for R1?