Zener diodes

[s-petersen]

I am trying to upgrade my Heathkit SP-5217 HV power supply to a SP5217a, I was trying to change the 0A2
gas discharge regulators to a 150v zener. The zener simply plugs in pins 1 and 7 of the tube socket.
The Zener is rated for 5 watts, and only 14MA flows through it, so only about 2 watts.
My problem is the diode gets extremely hot, I don't understand why it would get so hot if it is well within it's ratings.
I am looking for a suitable heatsink, for a DO-15 diode , I can just go back, but there is no fun in that.

 

[elnaldo]

2 watt in that small body is a lot of heat. Being within specs doesn't mean it will stay cool.

 

[s-petersen]

So is deigned to run that hot and last? With a improvised heatsink I'm getting temps of 170F

Edit: China strikes again... The diode according to the datasheet is supposed to be about 5mm in diameter, but this one is 3, so it is likely only a 2 watt device in reality.
OK, so I will have to heatsink it properly if it will last.
Thanks!

 

[arts]

Audio Research had similar problems with heating,and resorted to using a string of 47v types. Also,the higher voltage Zeners tend to be rather noisy,which was also a consideration.If you want quiet,you need to use a bunch of lower voltage types in series.

 

[s-petersen]

That's what Heathkit did originally with 5 27v zeners for each 0A2, I thought they did that because the parts were not available at the time.

 

[OMGCat!]

It probably wouldn't be hard to string a bunch of low voltage ones together with a bit of bread board and solder two pins to the bottom to mount into the socket.