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Vacuum Tube Audio Gear
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audiofanman
Sep 02, 2024
In Questions & Answers
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...
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audiofanman
Oct 18, 2023
In Questions & Answers
I decided to buy all of the iron from Thermionic Lab figuring go big or go home...
The specs provided by them, 425-400-0-50-400-425 Vac/160mA was a bit of a surpise,
They offer more voltage is better option lol... The Hammonds are 400V--
Stephi mentioned in one of the vidios that she might try using a solid state rectifier to see what the KT120s could do...
I dont plan on solid state rectificaiton using the 425v
SInce her B+ is 495 Im guessing I mught get about 520V...
That got me thinking about what changes (if any) might need to be figured in if I decided to wire up the 425v taps..
Increase the value of the plate resistor to the 6JC6A to keep the published 220V at that plate ?
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audiofanman
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