Andrew VK3BFA wrote:

Paul M0EME wrote:
Im building a HF linear using four PL519's. Can i use 2oz copper PCB for the
base to fit the valves too?????? as Im not very good at cutting and messing
with metal.


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Hi Paul,
you can - but not recommended. Valves generate a lot of heat, and PCB
is not good at dissipating it - would have problems very soon.

...while others say "Go ahead".

For this application I'd agree with Andrew - the PC board is going to
get HOT! I discovered this a long time ago, with a little VHF
transverter that created much less than a tenth of the heat that a
300-400W PA will. Until then, I'd never appreciated how much we rely on
an ordinary aluminium chassis to dissipate heat from the valve bases, or
how well it does it.

Unless you use a blower is actively aiming to cool the board as well as
the valves, the fibreglass is going to stew, turn brown and warp.

Why not
use aluminium sheet - easy to work as PCB, - I get mine form a local
scrap merchant, they have pieces big enuff to build any chassis I want,
and its a lot stronger AND cheaper than pcb.

That's basically true, but it just takes longer, and I don't suppose
Paul will have all the metalworking tools we OFs have collected over the
years. The main point is to make sure you get *soft* aluminium, and also
try to get it cut to size. Or try to find some old radio gear that was
built with a chassis and cabinet, and rebuild inside that... another
honourable tradition.

There was once an SP station who soldered the bases of *ten* 807s on a
sheet of PC board for his HF amp. But that was in another century, in a
desperate country before the Wall came down. It can be done, but it
isn't a good example to follow.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek