Plotus wrote:

With the Hammarlund HQ120 that I recently purchased, If been having a
great time DXing on all the bands and learning the in's and out's of
this particular Vintage radio operation. However, yesterday I lost my
OD3 tube. While working, I noticed that it put off a what appeared to
be... ultraviolet or bluish colored light, and about mid-day the radio
quit working.

The OD3 is a cold-cathode regulator tube. It's supposed to be glowing
with a blue light, that is how you know it is working. You can tell it
is a cold-cathode tube since the first number is a zero, indicating it
has no filament.

Wondering what might have went out, I let the radio return
to room temp and later turned it back on with the top lid opened a
couple inches to view the bulbs in operation. From what I could see,
they all lit except the OD3 tube which I initally noticed because of the
color, so I asume that is the cause of inoperability.

No, it's a symptom that you have no high voltage going into the OD3,
either because it's not coming out of the transformer or because there
is a rectifier or droppin resistor gone bad.

I got online and
bought a tube kit which included a complete HQ120 tube-set. I have no
idea of course as to the lifespan of the old 'original' ....OD3 tube and
if it's 'is' original or has been replaced sometime in the life of this
radio.

It's fine, there's probably nothing wrong with and there's probably nothing
wrong with any of the other tubes either. Heat the thing up, pull the
bottom of the case, and get out the meter. Work back from the OD3 plate
pin to the plug and see where the voltage drops.

Back to the title of this post.... should one operate the HQ with the
lid opened for cooling or add additional fan cooling from an outside
source? Also I was operating this in an enclosed cabinet with sides, top
and back, with about 8-10" of open space all around the radio? The
inside temp of the room was probably 60 or so degrees, so it was typical
cool fall weather. SHOULD I also cool and have the hood open? and should
it be in a more open environment? Thanks.........

It won't hurt to keep it cooler and it might last longer, but if you run
it with the lid open, the RF performance will be degraded since you will
have defeated much of the shielding.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."