Math ?

[shooter]

so the 270 R here is/(might) be toast
https://el34world.com/Forum/index.php?topic=23662.0

I wondered how much current was needed to smoke it
went to ohm, found sqroot of (5w/270ohm) = ~ .136A
guessed at 50mA normal op, puts .136A ~ 2.7 times normal
but I'm 2nd guessing myself 

[sluckey]

Not enough info to bother with math. Did this resistor burn open in a flash or did it slowly cook for 30 minutes? If he follows your advice he will quickly find the reason that it's open.

[PRR]

Your math checks mine.

One quibble: at full 5 Watts the resistor should live 1,000 hours. The report says 5 minutes. So to match the report we might assume 7-10 Watts.

In any case, 136mA is WAY more than the amp should be running and more than the rest of the amp would enjoy. The 14W 6V6 would be over 47 Watts. The 470r 5W cathode resistor would be at 8.7 Watts. So we do not expect the 270r to fail first.

One gotcha: the 270 has the startup surge of C2. At standby-to-run we may have 400V on C1 and zero Volts on C2. The 400V difference appears on the 270r to make 592 Watts of momentary power. This *may* take-out a 5W resistor, especially if it has a bad internal joint.

[shooter]

One gotcha

I can live, and learn with that 
the exercise really doesn't have anything to do with the other thread 'sept my brain was fertilized and this math presented itself 

thx
dave