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TUBE Cooling? Yes or No?
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. |
TUBE Cooling? Yes or No?
"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 |
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