Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: markmalin on March 05, 2021, 02:32:44 pm

Title: Power tube Temp and Magnesium/aluminum chassis too high?
Post by: markmalin on March 05, 2021, 02:32:44 pm

This is kind of off the wall, but it's important and I'd value you'alls input


I'm building an amp that will be somewhat of an "art project".  This will be a single ended EL34 output section with a Plexi style preamp, solid state rectifier, so only the 3 tubes.  2 12AX7's in the preamp and an EL34 power tube.  The "enclosure" I'm using is magnesium/aluminum (a vintage engine piece).  I wanted to have the 12AX7's and the EL34 "peeking" out of the top of the enclosure, so the tube socket would be mounted maybe 1/2" to 1" below the surface, the tubes would stick out of holes in the "enclosure" surface.


My concern is, from what I can tell an EL34 may get up to 400-450 degrees F, and this will be class A, so idling hot.  Do I need to be concerned the magnesium lid that the tubes are sticking through might be susceptible to fire?  I don't know much about metal work and figured there are some engineers out there who might be able to advise me.


Thanks
Mark

Title: Re: Power tube Temp and Magnesium/aluminum chassis too high?
Post by: silverfox on March 05, 2021, 03:27:33 pm

The autognition Temperature of magnesium is 650 degrees-C. It then burns at a max temperature of approx 3100 degrees-C. However, in the presence of moisture, the temperature could be lower as Magnesium reacts with water to liberate Hydrogen. So be sure not to try and put a Magnesium fire out with water.

Maybe that's what happened in the Ritchie2000 Avatar where the amp blows up on stage after the pyrotechnic event. Or was the amp, the pyrotechnic event?



silverfox.

Title: Re: Power tube Temp and Magnesium/aluminum chassis too high?
Post by: PRR on March 05, 2021, 04:14:12 pm

> 650 degrees-C

1200 deg F.

Think: the hottest tube is not as hot as some parts of an engine. Besides the exhaust, the oil system can get very hot. But not magnesium burning hot.

Title: Re: Power tube Temp and Magnesium/aluminum chassis too high?
Post by: silverfox on March 06, 2021, 02:01:12 am

Quote from: silverfox on March 05, 2021, 03:27:33 pm

. . . .However, in the presence of moisture, the temperature could be lower as Magnesium reacts with water to liberate Hydrogen.

In part, just to clarify, the answer was: "whimsical exaggeration".

I accept your position. Not likely; due to the numerous other contributing factors that would have to be present, the builder should be fine with the use of the chassis part.

Jus sayin, you never know- https://youtu.be/6GYb4nDaGkM