[Milsurplus] IF Alignment BC-348R Amendment T.O. 12R2-3BC-112

[john p hutchins]

Group -
Now I go on to solve the problem with an overly sensetive Master 
Oscillator adjustment capacitor on band 6 @ 18Mhz.
Any input on what to do; or look for; would be helpful.
Thanks
John Hutchins


IF Alignment BC-348R Amendment T.O. 12R2-3BC-112
<>
Attach Signal generator to Mixer grid as per procedures outlined in T.O. 
12R2-3BC-112 section 5 Maintenance, page 5-6 paragraph 4,a. Initially 
alight IF to 915 KHz. Attach high impedance Volt meter >= 20Kohms per 
volt across Volume control 79-B. See editors note.

<>AVC-OFF-MVC set to AVC. <>

Switch Crystal off align to 915 Khz.
IF transformer 1, 117, Primary Bottom, Secondary Top.
IF Crystal transformer 2, 118, Primary Top, Adjust Phasing capacitor 8 
Bottom.
IF transformer 3, 119, Primary Bottom, Secondary Top.
IF transformer 4, 120, Primary Bottom, Secondary Top.
IF transformer 5, 122, Primary Top, Secondary Bottom. <>

Switch Crystal on.
Retune signal generator for peak reading on voltmeter meter. Re-Tune IF 
transformers using this setting. Older signal generators check drift and 
re center generator after tuning each IF transformer for peak voltage 
reading.

<>IF transformer 1, 117, Primary Bottom, Secondary Top. Check for Peak 
reading.
IF Crystal transformer 2, 118, Primary Top. Adjust Phasing capacitor 8 
Bottom. Check for Peak reading.
IF transformer 3, 119, Primary Bottom, Secondary Top. Check for Peak 
reading.
IF transformer 4, 120, Primary Bottom, Secondary Top. Check for Peak 
reading.
IF transformer 5, 122, Primary Top, Secondary Bottom. Check for Peak 
reading. <>

Center BFO capacitor 9, pointer up.
Check drift and re center generator. Switch BFO on. Tune coil, Primary 
Top. Listen for NULL check for Peak reading. Voltage may jump up a bit. 
Switch BFO off. <>

Adjust Band width of IF transformer 5, 122. <>
Check drift and re center generator. Take reading. I suggest +/- 3 Khz 
from Peak frequency. Set generator for low end Peak frequency – 3 Khz. 
tune Primary Top for peak voltage. Set generator for high Peak frequency 
+ 3 Khz Tune Secondary Bottom for peak voltage.

Editors Note:
This was not a "Stock" unit so <>Inserted S-Meter circuit composed of 
50uA Panel meter shunted by 220 Ohm resistor, .01 uf 100 WV capacitor. 
Inserted into the unshielded line connecting Volume control 79-B and 
junction of bypass capacitor 35-4, resistor 56-2, capacitor 11-19, Pin 8 
VT-93. This was used to align the radio. An additional .01 uf 100WV 
capacitor may be inserted between the unshielded line Volume control pin 
connection and ground. Twist wires and run to meter. The signal 
generator used URM-25D was driftig +/- 100 Hz as detected by the 
frequency counter. Crystal frequency centered at 915.700 Khz. While the 
manual states +/- 5Khz adjustment for IF transformer 5, 122 ; I chose 
+/- 3Khz. This should make better CW and SSB copy with the filter turned 
on.
<>