Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joesatch on March 18, 2025, 02:45:37 pm
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i was told from various sources that 1 watt plate resistors are fine. Well these 1 watt metal film i have are tiny! are you folks sure 1 watt metal film is enough? these things are the size of a grain of rice
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I just installed some of those, so I sure hope so….,
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bust out a breadboard, a 'lil math, test for smoke :icon_biggrin:
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i have doubts
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Some years back, over at Kevin O'Connor's tube amp forum, guys were having trouble with the small body resistors in the B+ power supply. They couldn't take it and were dying.
They went back to the larger body R's and then no more problems.
I don't trust them, the small sized body R's.
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Also check the voltage rating of resistors that you are wanting to use where there are big voltage swings
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For plate resistors, I think they're fine. As power or dropping resistors, I'm not so sure. I use them quite a bit and haven't had a failure yet.
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gonna use them in V1 and V2 plates. hopefully no issues. if i have trouble sleeping i'll pull em
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check the voltage rating
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check the voltage rating
350V probably not enough fml
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check the voltage rating
350V probably not enough fml
350v is okay for a preamp plate or cathode load resistor given the likely range of voltage swing. Wouldn’t use them as single bleeder resistors in the power supply tho.
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Well, they look smaller than what I'm used to, but not *THAT* bad
Time will tell on the longevity.....
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i was told from various sources that 1 watt plate resistors are fine. Well these 1 watt metal film i have are tiny! are you folks sure 1 watt metal film is enough? ...
The resistor's power-rating is about temperature-rise.
"When this resistor dissipates 1 watt, the body-temperature will not rise more than ____ degrees." And we de-rate the resistor to dissipate less than its rating to keep it cool.
The implication is something about this resistor's construction enables it to throw off heat-to-the-air faster/better than older designs, such that it does not need a big surface-area to lose heat to the air via convection (or as-much surface-area as older designs).
If you want to use a 5w resistor because you like the size & look, you can use a 5w resistor. Or get used to some newer ones being a lot smaller than what you used in the past (and assume you're gonna need a meter to verify their value, because reading the color codes is impossible).
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Just as a reference. I have been inside several two rock 100 watt amps and they use the tiny 3mm x 8mm KOA CF resistors on the plates of several preamp tubes.
They hold up fine and they are only 1/2 watt.
Here is the data sheet on them
https://www.mouser.ca/ProductDetail/660-CF1-2C683J
I was surprised when I saw them too!
Cheers
Guy