I have a radio on the bench at the moment that when turned on from a cold start has a scratchy kind of static that almost totally goes away as the set warms up. It only takes a minute or two and its pretty much gone but at very low volumes its still there. I thought maybe a tube so I changed all the tubes, no effect. It has been completely recapped and aligned and it does work really well. I am guessing its a resistor, any thoughs on how to track this problem down? Thanks
Greg

You might try Freeze Spray. Spray each resistor and listen to see if the static starts up again. Freeze Spray is a rapid cooler and could induce the "cold start" symptoms you have noticed.

Rich

:I have a radio on the bench at the moment that when turned on from a cold start has a scratchy kind of static that almost totally goes away as the set warms up. It only takes a minute or two and its pretty much gone but at very low volumes its still there. I thought maybe a tube so I changed all the tubes, no effect. It has been completely recapped and aligned and it does work really well. I am guessing its a resistor, any thoughs on how to track this problem down? Thanks
:Greg

Before you go on the hunt you may wish to make sure you dont have anything causing this in your shop. Turn off florescent lamps or incandescent lamps with dimmer switches on them in the area or on the same line. And anything with an ac motor running on the same line. Some radios are very sensitive to these.

Try to isolate where the noise is located. For example is it RF, IF or Audio. Since it occures when the volume control is turned down, I would suspect an audio component first. Pull the 6B7 audio tube and see if the noise remains. If it does then check the components around the audio output tube. If it goes away, check the components around the 6B7. Ground the grid cap of the 6B7, if the noise remains then it is most likely located in the one of the audio sections. You can also ground the grids of the IFs' and see which section eliminates the noise. Freeze mist (technician in a can) can be very helpfull, but a more systematic approach is usually the way to go. In some cases the power supply can cause noise through the whole set. Check the resistors, especially if they are octogon shaped, for proper value. Make sure the speaker isn't a suspect by connecting a temporary speaker. Happy hunting.
MRO

Thanks for all of the great suggestions, I will try them tonight.
Greg

:Try to isolate where the noise is located. For example is it RF, IF or Audio. Since it occures when the volume control is turned down, I would suspect an audio component first. Pull the 6B7 audio tube and see if the noise remains. If it does then check the components around the audio output tube. If it goes away, check the components around the 6B7. Ground the grid cap of the 6B7, if the noise remains then it is most likely located in the one of the audio sections. You can also ground the grids of the IFs' and see which section eliminates the noise. Freeze mist (technician in a can) can be very helpfull, but a more systematic approach is usually the way to go. In some cases the power supply can cause noise through the whole set. Check the resistors, especially if they are octogon shaped, for proper value. Make sure the speaker isn't a suspect by connecting a temporary speaker. Happy hunting.
:MRO

According to the Perpetual Troubleshooter Handbook: Sputtering when first turned on can sometimes be traced poor connections in the voltage divider resistor especially the tap suppling the 6B7. The book suggest replacing the divider resistor with seperate wire wound resistors of 10,000 , 6,000 and 5,000 ohms. (R18, 20, 19 on the schematic)
Give this a try: When the radio is on gently push on the divider resistor terminals with an insulated probe and see if the noise changes. Happy hunting
MRO