813 Rig, a Bit of Progress.....

[W2PFY]

This rig is turning out to be one of the best 813's rigs I've seen to date.

Did you ever see the one John KC2FXE built? It looks great

[WA1GFZ]

A few places I worked actually used thick brass posts with a hole down the middle for the lead. This would help pull heat away from the diode. The posts would be pressed into a PC board.  

[W7SOE]

Did you ever see the one John KC2FXE built? It looks great

That rig is bahyewtifull!!  Quite the behemoth.

Rich

[W2PFY]

That rig is bahyewtifull!!

And it a  JJ rig. Where did you find it?

[KC9LKE]

Very nice Rich!

Much envy here. No time now to work on mine, have to go back to the “Pen”
for 16 more weeks.
I like how You protected the PS switches with the rack handle. Keep up the good work!

Ted / KC9LKE

[W7SOE]

I found pictures of it in Bear's photo section.


Rich

[WD5JKO]

Just a side comment for others....the 1N5408 diode is only rated at its full 3A with at least 1/2" of lead exposed, with the way some sharply bend the leads right after the body and mount in a PC board seriously derates them. Rich has plenty of lead exposed, especially for that QRP amp

Carl, I think you got this backwards. The shorter the lead to a heatsink the better. The 1N5408 is rated to 75C @ 3A when the leads are .375" long, and soldered to a 20mm X 20mm X 1mm copper heatsink. The longer the leads the more we derate the diodes, not the other way around. Some examples:

http://doc.chipfind.ru/jgd/in5408.htm
http://sites.google.com/site/interfacebus/thermal-impedance/diode-lead-length-temperature
http://www.voltagemultipliers.com/pdf/Appendix%20B%20-%20Diode%20Thermal%20Analysis.pdf

The PCB designers need to provide fat traces big enough to act as a heat sink, and use short diode leads to get the heat from the diode to the heatsink. Longer is not always better.  

Jim
WD5JKO

[KM1H]

Nope, thats an absolute minimum length as a heat sink Jim. Mo is betta in a real world PC board or a hammy hambone perf board mount where the leads alone are the heat sink. Where would we be without perfboard anyway?

Here is the 1N5408's QRO fans big brother, note the 2 mounting procedure graphs.

Point an IR gun at either with a steady load and vary the lead lengths.

Carl

[WA1GFZ]

Ran that test about 35 years ago, but we didn't have an IR gun.

[K1JJ]

I use the 6A 1KV diodes for every PS here and don't worry about heat...

The price is close enuff to the smaller ones and they just laugh in the face of death...  

T

[KM1H]

Yep, and at .16 each in 100 qty at Mouser for MCC brand you can even afford to use them in place of a 1N4007

[K1JJ]

Are they THAT cheap now?  I used to pay a lot more at Silicon Valley - and was still happy...

I have a string of about 140 on my big HV supply. It's been FB for at least 20 years now.

T