Hi Is this the right chip: http://www.oemstrade.com/search/STEL-1173%252FCL/ At $65 it is pricy but a bargain if it fixes your clock. Thomas Knox
> Date: Mon, 5 May 2014 15:14:16 -0600 > From: ed_pal...@sasktel.net > To: time-nuts@febo.com > Subject: Re: [time-nuts] Datum 4065A Cs Tube Response > > I know very little about today's DDS chips, but I think that emulating > the STEL-1173 would be a challenge. It provides 48 bit frequency > resolution. I counted 13 different frequencies that are used to monitor > the signal to make sure that it's on frequency. Based on the manual, > they were shifting it many times per second. I'm not surprised the chip > died - they worked it to death! > > Ed > > On 5/5/2014 6:49 AM, paul swed wrote: > > I will agree with Joe. I have a CS tube thats darn near impossible to read > > the beam current and yet it still locks. That truly amazes me. I seem to > > recall other comments ages ago about that chip failing. There should be a > > way to emulate it these days with all of the DDS chips and such that are > > available. > > Good luck. > > Regards > > Paul. > > WB8TSL > > > > > > On Mon, May 5, 2014 at 8:20 AM, J. L. Trantham <jlt...@att.net> wrote: > > > >> Ed, > >> > >> If I have the math correct, and you are measuring the voltage to ground > >> through a 10 MegOhm input impedance DMM, you have about 7.5 nA beam current > >> which seems a bit low compared to what I remember of the HP 5061A. > >> However, > >> you still have a definable 'peak' with a 'peak to valley' voltage of about > >> 60 mV or a 'useful signal current' of about 6 nA. If your unit's circuitry > >> can properly amplify that and keep it a clean signal, it should work. > >> However, I would recommend setting the OCXO precisely on frequency with a > >> GPSDO before trying to close the loop and 'locking' the signal to the CS > >> tube. It will dramatically lower the work load of getting everything > >> adjusted properly, particularly in a setting of low beam current. > >> > >> Somehow, the value of 40 nA sticks in my mind from the 5061A. The 5061A > >> manual says end of life of the HP CS tube is a peak beam current of 8 nA or > >> less. However, I have units with less current and they still lock. The HP > >> manual also says to measure the voltage at the output of the tube with a > >> 100 > >> MegOhm or higher input impedance DMM. If yours is less, that may > >> artificially lower your values. > >> > >> EOL of the tube is a multifactor issue, including Signal to Noise ratio and > >> the 'useful signal current' to 'background current' ratio. The 'background > >> current' is what you see with no RF signal applied to the tube. Have you > >> measured that? A ratio of 1 is EOL per the HP manual. If yours is about > >> 4.5 nA, as suggested by the 'off peak' values shown, or less, you still > >> have > >> a useful signal and, hopefully, a useful tube. > >> > >> I'd recommend continuing with the repair. > >> > >> Good luck. > >> > >> Joe > >> > >> -----Original Message----- > >> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > >> Behalf Of Ed Palmer > >> Sent: Monday, May 05, 2014 12:46 AM > >> To: Discussion of precise time and frequency measurement > >> Subject: [time-nuts] Datum 4065A Cs Tube Response > >> > >> I'm playing with my first Cs standard. It's a Datum 4065A which appears to > >> have a dead STEL-1173 synthesizer. Before I put too much effort into > >> replacing that, I thought I'd check the tube and see if it has any life > >> left. I've attached a chart showing the response of the central peak. > >> > >> My methodology was similar to TVB's as shown here: > >> http://www.leapsecond.com/pages/cspeak except that I measured the tube > >> output directly with a digital voltmeter. The system is reporting wildly > >> varying levels for the beam current so I didn't want to use any of it's > >> circuitry. > >> > >> Does this look like a usable tube? Healthy or on it's last legs? What > >> response levels are typical for a Datum 7504A tube? I see that these > >> levels > >> are somewhat lower than those shown on leapsecond for the 5061A tube, but > >> that could just be the specifics of the measurement. > >> > >> Thanks, > >> > >> Ed > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.