Jeez, this is not rocket science ! This instrument is old enough to have used the common "Allen Bradley" carbon composition resistors of that day. These puppies are famous for changing value due to humidity without ever passing any electrons through them.
If the voltage is relatively close and the regulator is regulating, then it is most likely the old carbon resistors used in the "sense" string have changed value. I kind of hate to suggest doing some component jumping, as I think you may be out of your league here. If you have a schematic, I was unable to find one on the internet, there are a number of ways, using clip leads, to check the regulation circuitry. You really should fully understand regulated power supplies and know what you are doing if you try this sort of thing. BUT, the first step is to see if the "input" voltage to the main pass element is higher then the output side of the pass element. The differential amount should be way in excess of 3 volts. I.E., if it is an expected 18 volt regulated output then the input is going to be around 24 to 28 volts. This was normal back in those days ! Following this thread has been giving my one cell brain a headache. Every wrong step has been done so far to troubleshoot, IF IT WAS REALLY NEEDED, this instrument. It is beyond me how you could consider changing the temperature settings (the hardest process) before verifying everything else. Particularly without waiting the required time for such an instrument to stabilize its temperature; at least a 2 to 3 month time frame. I am sorry for ranting in such a manner, but everyone else, except for one or two, have been doing the same thing. All that is happening is to further exacerbate the problem. I will quit ranting now. Bill....WB6BNQ [email protected] wrote: > In a message dated 08/08/2009 09:53:35 GMT Daylight Time, > [email protected] writes: > > Getting one. > > So far I've found places with $300 minimum buys. > > However, as I write I can get one for $30 including postage to > Australia. Still expensive. > > Unless anyone has a 2N1701 lying around? > > Two questions...... > > First, how desperate are you to replace it with the same part? > >From a quick look at the device spec it would seem there's a variety of > devices would do the same job, perhaps a 2N3055 for example?, the hardest part > might be matching the shape but where it's mounted would determine how > necessary that would be. > > Second, unless I've missed something somewhere, are you sure it needs > replacing? > >From what I remember of previous postings I thought you'd said the voltage > was high, but also seem to recall it being pretty close. > Have you checked the transistor, or just measured either side of it to see > if it seems to be regulating? > A voltage a bit high or low on a regulated supply usually indicates just a > need for adjustment. > If there's no adjustable preset it might indicate the designer didn't > consider the absolute value to be that critical anyway. > > regards > > Nigel > GM8PZR > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
