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![]() "ablebravo" wrote in message ups.com... thx richard. esp on how to test the coils. i will do that before checking the IF again. i am suspecting the IF because a couple of the adjustments were near the travel limit, which may mean i am in wrong place. where it works, it's hot. i was pretty sure on the tuning gang -- could adjust the vanes and get the crackle to change and nearly disappear. i flushed it good, blew it out and cleaned and cleaned. after spending hours on it, i bought the part. i think something might have been in the bearings. in the 'crackle spot' the signal died and set could not be aligned. it blotted out some of the align freqs. no such prob w/replacement part. ab Do you have a signal generator of some sort? I thought from your posts that you do. You really do need one to set up the IF amplifiers. It should be capable of putting out 455 khz preferably with some modulation. The usual requirement is for 400hz at about 30%. The modulation level is not critical but most signal generators are not capable of high modulation level. Its also helpful to have a crystal calibrator, preferably one which puts out fairly low frequency markers in addition to higher frequency ones. 10khz is nice to have. Mine has 100khz, 1.0 mhz, and 10mhz. This can be used directly to calibrate the receiver and also to calibrate the signal generator. If you don't have these tools perhaps you can borrow them. If the IF transformers are near the limit of their adjustment, and you know the test frequency is correct, its probable the resonating capacitors have drifted in value. I believe this receiver uses permeablility tuned IF coils (asjustable dust cores). Again, since the problem seems to be isolated to two bands and at least one band works OK I think the IF is not at fault, or at least not the main cause of trouble. I suggest checking the wiring of the tuning capacitor again to make sure its OK. You might want to check the other capacitors in the oscillator and RF stage. I am suspicious of the oscillator because you say it quits near the low end of one band. That sound to me like a bad coupling capacitor there. If you have access to a good RF voltmeter or reasonably wide band oscilloscope you can check the output of the oscillator. Even a pick-up loop will show if the output is varying a lot or if the LO is quitting at the low end of a band. Just some things to look for. Remember, this RX is more than fifty years old so it may have a lot of tired parts (so do I). -- --- Richard Knoppow Los Angeles, CA, USA |
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