On Nov 26, 9:31*am, Edward Knobloch wrote:
On 11/26/2010 9:48 AM, Plotus wrote:

snip *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. 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. snip

Hi,
An 0D3 tube normally glows blue or pink when operating.
It is a gas-filled voltage regulator,
and operates like a 150V Zener diode.
The fact that the 0D3 is now dark and your radio has stopped working
indicates that you have lost the dc supply in your HQ-120.
I'd look carefully at the electrolytics in your power supply,
one may have developed a short.

73,
Ed Knobloch

My guess would be the the dropping resistor in series with the 0D3.
The 0D3 probably supplies the oscillator and possible the bfo tubes.
So, they won't work and you won't receive anything. However, you
should be able to still get some sound from the audio stages.

The other possibility is the rectifier died and then you will not have
any audio output and the 0D3 will not light. Look for the heater in
the rectifier, 5Y3?, should be glowing.

If you detect a bad smell, then it is more serious!

Paul, KD7HB