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Title: Collins 51J-4, BFO frequency fault? --FIXED-- Post by: SM6OID on September 21, 2010, 02:52:07 AM Yesterday when I fired up one of the 51J-4’s that I use frequently, I noticed the following.
It seems to me like the BFO frequency has shifted about 1 kHz from the centre setting. Is there a known cause for this fault? I know for sure that it was OK a while ago. Title: Re: Collins 51J-4, BFO frequency fault? Post by: k4kyv on September 21, 2010, 09:30:04 AM I'm assuming the 51J4 is somewhat like the 75A-4, but I don't think it has the passband tuning feature.
Before adjusting any trimmers, make sure the BFO knob hasn't simply slipped on the shaft. If you are sure that is not the case, there should be trimmer capacitor or tuning slug that tunes the BFO oscillator coil, accessible right on the shield can. Set the BFO knob to the centre setting, and then adjust the BFO to the proper frequency by turning the trimmer or tuning slug. If you re-adjust it but notice a while later that the frequency is off again, you may have a flaky fixed mica capacitor, which might be located inside the BFO can. Those little red micas used by Collins are notorious for becoming leaky and/or intermittent. Check the manual and schematic first, if you have one. Title: Re: Collins 51J-4, BFO frequency fault? --FIXED-- Post by: SM6OID on September 30, 2010, 12:06:03 PM Hej !
Well, I took a look at it today... AND, either the knob or something else slipped on the shaft. So, simply resetting the mechanical position I was back in business. Now I have to fix the BFO frequency on one of my R-390A's, but that is another story... Conclusion, as always, start from the very beginning when doing fault tracing. Title: Re: Collins 51J-4, BFO frequency fault? --FIXED-- Post by: w3jn on September 30, 2010, 02:39:09 PM The R-390's easy. Tune in a xtal cal marker for max signal strength with the selectivity in .1 KC position.
Remove the BFO knob, turn on BFO, zero beat the signal using the BFO shaft, replace knob with the pointer straight up. There is no other adjustment for the BFO freq. Title: Re: Collins 51J-4, BFO frequency fault? --FIXED-- Post by: SM6OID on September 30, 2010, 02:59:40 PM Hej !
Thank's ! I will take care of that right now! Title: Re: Collins 51J-4, BFO frequency fault? --FIXED-- Post by: SM6OID on September 30, 2010, 03:15:08 PM Done! :)
Title: Re: Collins 51J-4, BFO frequency fault? --FIXED-- Post by: w3jn on September 30, 2010, 04:41:15 PM And you don't even have to open the hood to do it ;D
Title: Re: Collins 51J-4, BFO frequency fault? --FIXED-- Post by: SM6OID on October 01, 2010, 08:02:01 AM Hej !
Well, it was too easy! But I will open it up in a few day's, to replace the big capacitors C603 and C606 plus the tiny C609. Later I must clean and relubricate the geartrain and so on, and of course give it a complete check up. Any advice were to find Sprauge Yellow Drop? At a reasonable price. Remember that the stuff must be sent to Sweden... Customs and VAT (25%) will add the final cost significantly. :( Title: Re: Collins 51J-4, BFO frequency fault? --FIXED-- Post by: w3jn on October 01, 2010, 08:53:11 AM I believe companies like Mouser and Allied have distributors in the EU. You might look for a EU-based seller on eBay.
Do you have to pay VAT and customs on gifts? Let me know what you need, I could just send you a few via international mail. Title: Re: Collins 51J-4, BFO frequency fault? --FIXED-- Post by: KM1H on October 01, 2010, 02:46:46 PM I can also facilitate getting items into EU by sending to my son in Germany by APO military mail, costs the same as mailing to NYC.
At the moment he is in Prague and then heading to Kiev for a month before returning. Carl Title: Re: Collins 51J-4, BFO frequency fault? --FIXED-- Post by: SM6OID on October 03, 2010, 07:11:40 AM Hej ! AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
I am VERY happy that there are people out there willing to help! I will see if I can "solve the problem" my self, otherwise you will here from me! Once again, thanks! |