You need to have cool air moving across the tube base pins. The
conventional method of under-up cooling supplies the base pins
with safe cooling. If you blow into the anode, what happens to
the air reaching the base pins/contacts? The seal around the
tube base contacts also needs cooling and it should not be already
hot air from passing by the anode.

Smaller tubes are forgiving in cost and operation. Jump to
the 4cx1000/4cx1500 size and you had best not over heat the
tube, both base pins and anode.

cheers,
skipp

www.radiowrench.com/sonic I have a diagram of the Collins 30S-1 available
(as well as many others).



: Patrick wrote:
: Hi All,

: I'm about to build a 4CX1500B amplifier for 2m.

: Most, if not all, descriptions are blowing air into the enclosure on the
: base side of the tube and the air goes through the socket and finaly
: through the anode chimney.
: For several reasons i would like to blow into the anode enclosure
: directly onto the anode, the air would then go out through the anode
: chimney. Only a small part of the air would cool the base of the tube
: through small holes in the anode/cathode separation.

: Is that a stupid idea ? Is there any reason not doing so ?

: 73, Patrick