Are you sure the oscillator is operating? Sometimes it's possible to force through strong local stations without the osc operating. In this case tuning may act more like a volume control.
See if you can pick up the osc signal on a second radio, IF frequency above the dial marking.
Polarity of the osc coil has to be correct to get oscillation. May need to reverse wires on one winding to get oscillation?
Norm
:I have recapped and changed resistors as required, installed a solid state vibrator and added new buffer cap. I have 212v at the rectifier. The manual oscillator coil was open, fixed that and the tuning condenser came to life. My problem is that I can only receive at 1570 kc and 1120kc at the same time and nothing else anywhere on the dial. When the presets are selected, nothing on the first 2 (580 to 1050kc) 3 is a weaker version of 4 and 5 (900 to 1580) which are loud and clear with 2 stations which sounds exactly like manual dial. The 1570 is a very strong local station. I noticed that the 2 station I receive are 455 kc apart. Alignment? The Philco sheet says to send 455kc thru .1mf cap to the antenna receptacle. I did that and the maximum output is where I have it, but no change in reception. I really like to figure as much of this kind of stuff out myself, but this beyond my diagnostic ability. Thanks for your thoughts
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73's de Edd |
:Hi Bob
:
: Are you sure the oscillator is operating? Sometimes it's possible to force through strong local stations without the osc operating. In this case tuning may act more like a volume control.
:
: See if you can pick up the osc signal on a second radio, IF frequency above the dial marking.
:
: Polarity of the osc coil has to be correct to get oscillation. May need to reverse wires on one winding to get oscillation?
:
:Norm
:
:
::I have recapped and changed resistors as required, installed a solid state vibrator and added new buffer cap. I have 212v at the rectifier. The manual oscillator coil was open, fixed that and the tuning condenser came to life. My problem is that I can only receive at 1570 kc and 1120kc at the same time and nothing else anywhere on the dial. When the presets are selected, nothing on the first 2 (580 to 1050kc) 3 is a weaker version of 4 and 5 (900 to 1580) which are loud and clear with 2 stations which sounds exactly like manual dial. The 1570 is a very strong local station. I noticed that the 2 station I receive are 455 kc apart. Alignment? The Philco sheet says to send 455kc thru .1mf cap to the antenna receptacle. I did that and the maximum output is where I have it, but no change in reception. I really like to figure as much of this kind of stuff out myself, but this beyond my diagnostic ability. Thanks for your thoughts
::
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: : : :  : : : : : : : :Sir Bob . . . . . : : : :" I did that and the maximum output is where I have it, but no change in reception" : : : :That info at least confirms that you HAVE an RF signal generator to do further exploration with. : : :And the explained situation still reeks of the local oscillator not being operative and the signal just barreling on thru the mixer stage in a TRF'ing mode . . .so why not lets try this: : : :Confirm that the 7B8's cathode is about ~850ohms above chassis ground. : : :That your osc grid coupling capacitor item 15 is ~250 pf with no leakage.(vwery unlikely on a probably S.M. unit being used ). : : :That your oscillator "plate" resistor item 16 is ~ 24K ohms : : :.That your cathode bypass condenser item 13 is bypassing. : : :That your item 20 B+ bypass condenser is bypassing : : :The last two tests can be initiated by supplementally shunting across the caps with another unit, while confirming a change in reception on the radio. : : :If the above situations are not concisive . . .thennnnnnn . . . : : :Look at the bottom connection of osc grid coupling capacitor item 15 and either snip that one connection loose or unsolder it. : : :With you having that 1570 as being probably your strongest local station received, consider your next two strongest signals and :take the strongest next station we considered above. . : : :Then you figure out + 455 khz added to its frequency and clip your signal gen into that bottom floating cap lead and set the sig gen scale to the computed Rec stat + 455 khz , and set to UNMODULATED / CW output level and then inject that computed oscillator frequency. : : :If the radio dial is guesstimated to the desired radio station to be received and the sig gen "injection" level is gradually brought on up in strength to a proper threshold, your station should start coming in on the radio. Tweak in the car radio station manual tuning and Signal generators osc tuning for best reception. : : :Your other stronger stations could be confirmed in the same manner . . . . . thereby positively confirming that you still have a "buggy" situation in the sets local oscillator section. : : : :73's de Edd : : : : :It’s not an optical illusion. It just looks like one. : : : :  : : : |
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::Hi Bob
::
:: Are you sure the oscillator is operating? Sometimes it's possible to force through strong local stations without the osc operating. In this case tuning may act more like a volume control.
::
:: See if you can pick up the osc signal on a second radio, IF frequency above the dial marking.
::
:: Polarity of the osc coil has to be correct to get oscillation. May need to reverse wires on one winding to get oscillation?
::
::Norm
::
::
:::I have recapped and changed resistors as required, installed a solid state vibrator and added new buffer cap. I have 212v at the rectifier. The manual oscillator coil was open, fixed that and the tuning condenser came to life. My problem is that I can only receive at 1570 kc and 1120kc at the same time and nothing else anywhere on the dial. When the presets are selected, nothing on the first 2 (580 to 1050kc) 3 is a weaker version of 4 and 5 (900 to 1580) which are loud and clear with 2 stations which sounds exactly like manual dial. The 1570 is a very strong local station. I noticed that the 2 station I receive are 455 kc apart. Alignment? The Philco sheet says to send 455kc thru .1mf cap to the antenna receptacle. I did that and the maximum output is where I have it, but no change in reception. I really like to figure as much of this kind of stuff out myself, but this beyond my diagnostic ability. Thanks for your thoughts
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