Build
this as close to the mixer as possable and before the loopstick or
sensitivity will be lossed, do to the radio's own RFI.
** The lighter pf part of the gang should go to the oscillator, the heavier side goes to the loop; don't mix them up!
Pin 5 goes to ground, Pin 6 goes to the oscillator, and pin 4 goes to the AF stage.
Testing:
Connect the output to the ocilloscope, a sine wave should appear, if not you might want to try to switch the polarity of the transformer IF-300. (Some oscillator (and even IF) coils in instances one side is sometimes wound backwards for some reason).
Make sure when you sweep across the gang capacitor the waveform should be continuous, if it is not try a different transistor (some general purpose transistors suck at low voltages).
NOTE: Your gang may not be able to tune to 1700, you may want to change the top frequency to 2055 instead of 2155, or the antenna side will not tune as high as your oscillator goes.
Alignment:
(If you changed the 160 pf cap with a trimmer)The trimmer pf cap is width
The cap on the back of the gang is hight
The IF 300 core is the bottom frequency.
Put a frequency counter on the output.
Step 1, Tune the gang to it's lowest point (all the way counter clockwise).
Step 2, Tune the core of IF 300 so that the bottom frequency of the gang (all the way counter clockwise) is 995KHz; you may have to adjust the width trimmer cap (if used instead of the 160 pf cap try to get it so the oscillator transformer's core is as close to the middle as possable).
Step 3, Tune the trimmer on the back of the gang so that the highest point of the gang (all the way over clockwise) is at 2155 KHz (or 2055)
Repeat untill the range is 995 - 2155 (or 995 - 2055)
* Why am I tunning the radio between 995 - 2155 (or 995 -2055), if the range of the radio is 540 - 1700 (540 - 1600) ?
Remember the frequency of the IF was 455KHz, 995 minus 455 = 540; this is the intermedite subharmonic frequency that will be bounced to 455KHz.
In circuit:
Connect the output to the "Oscillator in" of the first IF / mixer stage.
** The lighter pf part of the gang should go to the oscillator, the heavier side goes to the loop; don't mix them up!
Here is a data sheet of a
BC-88 Gang cap (doctored) from www.oselectronics.com
most gangs use this pin configuration; the AM cap (BC-540) from Ocean
State Electronics is the same it just doesn't have the FM side.
Pin 5 goes to ground, Pin 6 goes to the oscillator, and pin 4 goes to the AF stage.
Testing:Connect the output to the ocilloscope, a sine wave should appear, if not you might want to try to switch the polarity of the transformer IF-300. (Some oscillator (and even IF) coils in instances one side is sometimes wound backwards for some reason).
Make sure when you sweep across the gang capacitor the waveform should be continuous, if it is not try a different transistor (some general purpose transistors suck at low voltages).
NOTE: Your gang may not be able to tune to 1700, you may want to change the top frequency to 2055 instead of 2155, or the antenna side will not tune as high as your oscillator goes.
Alignment:
(If you changed the 160 pf cap with a trimmer)The trimmer pf cap is width
The cap on the back of the gang is hight
The IF 300 core is the bottom frequency.
Put a frequency counter on the output.
Step 1, Tune the gang to it's lowest point (all the way counter clockwise).
Step 2, Tune the core of IF 300 so that the bottom frequency of the gang (all the way counter clockwise) is 995KHz; you may have to adjust the width trimmer cap (if used instead of the 160 pf cap try to get it so the oscillator transformer's core is as close to the middle as possable).
Step 3, Tune the trimmer on the back of the gang so that the highest point of the gang (all the way over clockwise) is at 2155 KHz (or 2055)
Repeat untill the range is 995 - 2155 (or 995 - 2055)
* Why am I tunning the radio between 995 - 2155 (or 995 -2055), if the range of the radio is 540 - 1700 (540 - 1600) ?
Remember the frequency of the IF was 455KHz, 995 minus 455 = 540; this is the intermedite subharmonic frequency that will be bounced to 455KHz.
In circuit:
Connect the output to the "Oscillator in" of the first IF / mixer stage.