[Milsurplus] LM/BC-221 stability

[John Hutchins]

Larry -


I have models of the BC-221's and the LM 13&14's put a freq counter on 
the Audio leave it  and com and check it between commercials, mine will 
drift up and down a few 200 hrtz after a 1 hour warm up. If greater than 
that then I suspect the NPO cap across the coil is bad.  In the BC221-AK 
cap #5 and poisibily #6  I believe are NPO's?   I spent a whole week end 
plotting every 10 minutes the frequency drift on a BC-221-AK, just 
because....

Hutch

On 1/6/2014 6:49 PM, Larry wrote:
> I now have my LM-14 freq meter wired up and heated up as well.  One of 
> the things i've been watching the past few days is the stability of it 
> when calibrated or in the Calibrate mode.
>
> I notice that even with a good regulated power supply, i can set the 
> voltage to anything in the 200V range but presently its setting at 
> about 225V for plate and 24V for the filament.  It still has some 
> drift.  My question is, "how long after the unit was calibrated to a 
> particular check point did the techs wait before going back and 
> rechecking it"?  Was it allowed to drift 1 or 5 or however many KC 
> before they were concerned or did the do it regularly, say every 5, 10 
> or 15 minutes.  What would the requirement have been?  Saying that 
> they only used to to check one frequency on a bunch of receiver as an 
> instance?  Course if they were moving it from one freq to another i'm 
> sure they rechecked the Cal every time the moved it to a new freq.
>
> I'd think that with the wide bandwidth of the receivers that even if 
> it was off several KC it wouldn't have been a major item. Also, how 
> far off frequency do you think a receiver would have had to be before 
> it was reported to the main crew? I think it was said on here before 
> that sometimes crew members "diddled" with the tuning if they weren't 
> hearing other transmissions like they thought they should. Another 
> factor to consider.
>
> I've not yet put a freq counter on it to watch and see how far it 
> moves but that is coming up.
> Otherwise i think it's pretty reliable, if you leave the B+ on.
>
> Larry
> W0OGH
>
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