[Elecraft] KPA-1500 Fan Noise - YouTube ?

[N2TK, Tony]

George, there is nothing like Eimac Orange with a glass bottle. RF sunburn
:-)

Hey, transistors can run pretty hot too, although they should not melt the
solder. Case temp can get to 150 deg C and junction temp to 225 deg C. Yes
your finger will burn on the case. And yes, the life of many power devices
gets derated based on junction temp. As an example  an LDMOS may have an
MTTF of 1M hours at 150C and 70K hours at 225C junction temp. JANS space
transistors are burned in at 220C and tested up to 125C case temp.

N2TK, Tony

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Gmail - George
Sent: Saturday, June 02, 2018 8:10 AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] KPA-1500 Fan Noise - YouTube ?

One other thought to keep in mind - solid state amps need a lower delta T
than tube amps. Tubes like to run hot - solid state devices not so much.

I've seen a tube with the fins so hot that the solder was in globs, while
the transmitter was still operating. I doubt any solid state final would
have survived that heat.

When we installed our solid state TV transmitter, it was a new learning
curve in cooling. Both transmitters were 30 kW class AB1. The tube
transmitter moved air faster through 3 tubes but had almost 3 times the
temperature rise than the specs for the solid state transmitter. Our HVAC
company and architect worked on several complex systems with air mixers
until we just decided to use wall mounted air conditioners into the room
behind the transmitter racks and exhausted to the front of the transmitters.

Our solid state transmitter did meet the OSHA limit for 8 hours exposure to
noise but just barely. It was very noisy compared to the tube unit.

No tube transmitter I have ever used had a temperature shut down on any of
the tube stages.

73 George AI4VZ



-----Original Message-----
From: Don Wilhelm

Only one bit of correction.  If the output power is 1500 watts and the
efficiency is 50%, that 1500 watts is only half the total power consumed, so
there is 1500 watts of power that must be exhausted as heat.

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html Message
delivered to tony.kaz at verizon.net