I hace noticed however, when I attach an antenna to the radio and crank up the input pot to get gain, the gain goes up in "blocks" i.e. low gain at first quarter turn, mid-gain at second quarter to a third turn and high gain at the end of travel. I thought this was a variable resistor that varied the antenna signal into the first RF stage "smoothly".
If I grab the bare input shaft of the pot and act as the antenna myself, it does work smoothly.
What gives with this one? I am at a loss, and I have seen this behaviour on other TRF sets.
Lou
A frequent problem with this set is that the volume control won't sufficiently cut the volume for nearby stations. This is caused by the RF signal jumping straight into the chassis, bypassing the volume control and any antenna altogether. The fix for that problem is to rig up shielding in back of and under the chassis.
Schematic: http://www.nostalgiaair.org/PagesByModel/317/M0040317.pdf
Doug
:Well, the Radiola 18 is coming along nicely.
:
:I hace noticed however, when I attach an antenna to the radio and crank up the input pot to get gain, the gain goes up in "blocks" i.e. low gain at first quarter turn, mid-gain at second quarter to a third turn and high gain at the end of travel. I thought this was a variable resistor that varied the antenna signal into the first RF stage "smoothly".
:
:If I grab the bare input shaft of the pot and act as the antenna myself, it does work smoothly.
:
:What gives with this one? I am at a loss, and I have seen this behaviour on other TRF sets.
:
:Lou
Well, being a "purist", I think I will leave the design as-is. The only thing I may do is to check the resistance of the input pot as it varies througout is rotation.
It DOES have a nice wood cabinet!!
Lou
:Lou: I can't explain exactly the symptoms you describe. However, the volume control is in the antenna ckt. That is a very poor design and leads to flakey performance.
:
:A frequent problem with this set is that the volume control won't sufficiently cut the volume for nearby stations. This is caused by the RF signal jumping straight into the chassis, bypassing the volume control and any antenna altogether. The fix for that problem is to rig up shielding in back of and under the chassis.
:
:Schematic: http://www.nostalgiaair.org/PagesByModel/317/M0040317.pdf
:Doug
:
:
::Well, the Radiola 18 is coming along nicely.
::
::I hace noticed however, when I attach an antenna to the radio and crank up the input pot to get gain, the gain goes up in "blocks" i.e. low gain at first quarter turn, mid-gain at second quarter to a third turn and high gain at the end of travel. I thought this was a variable resistor that varied the antenna signal into the first RF stage "smoothly".
::
::If I grab the bare input shaft of the pot and act as the antenna myself, it does work smoothly.
::
::What gives with this one? I am at a loss, and I have seen this behaviour on other TRF sets.
::
::Lou
Perhaps there are some breaks in the resistance element of the pot or corrosion along the path of the wiper. Check it with a meter as you have mentioned. Disassembly and a good cleaning (including the shaft and contact points of the wiper)may improve performance....