"Kenneth Scharf" wrote in message
...
On 11/26/2010 09:48 AM, 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. 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. 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.
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.........
Plotus AKA Richard...
From the descriptions I've heard your problem is that the
power resistor in series with the OD3 has opened up. The
OD3 is used to regulate the voltage to the oscillator
section(s) of the receiver, and with that resistor open
the OD3 gets no power and won't light, the oscillator in
the receiver gets no power and won't work. You will still
get a hum out of the receiver as the AF section is still
alive, in fact if you touch the center terminal of the
volume control with a finger (through a .01uf cap so you
avoid touching B+) you should get a LOUD hum. With the LO
and BFO sections dead, a superhet will receive NOTHING
(well if you inject a modulated 455khz signal to the
antenna you should hear THAT).
Look under the chassis for a rather black resistor
connecting to the 0D3 socket. Usually resistors don't go
bad unless there is something else wrong, but on an old
set like this all bets are off.
The resistor is a 3K, 10W, wire wound. Wire wound
resistors often go open because the joint between one end of
the winding and the terminal on the resistor has opened up
due to corrosion of the weld. Sometimes they can be fixed by
soldering at the joint. Otherwise, this is a pretty standard
value resistor and should not be difficult to replace. If
its just opened up it may look just fine. If it burned up
you would probably smell it. Also check the solder joints to
at the ends of the reisistor and at the terminals of the
regulator tube. These can run hot and fail after a long
period of time.
You may find that wiggling wires around the regulator
may bring it back to life, thats one way of showing up bad
solder joints.
You need a decent voltmeter to do even rudimentary
trouble shooting. They are available cheap from Radio Shack
and other sources. You don't need anything fancy. You may
find that a modern meter will read higher than the voltages
in the chart for the receiver. That's because the meter used
by Hammarlund, and specified by them, has rather low
resistance compared to a modern meter so it affects the
readings more.
--
--
Richard Knoppow
Los Angeles
WB6KBL