The Zeeman frequency is calculated by the amount of C-field current you use. If you change the Zeeman then to get the unit "on frequency" you then have to change the synthesizer frequency and the C-field current to compensate. The amount of C-field change is too big for the front panel knobpot so a resistor change on the A15 board is required. The earlier 5061A current (61miiliGauss) resulted in a synthesizer frequency of 12.6317716 Mhz giving a corresponding Zeeman frequency of 48.82Khz. On later 5061A and B units HP decided that using a different current (76 milliGauss) that was more stable which ended up giving you 12.7317725Mhz and 53.53Khz. There is NO difference in the tubes C-field winding (for 5061A/B and 5071A). The current set resistor on the A15 board and the synthesizer frequency are the only change. Corby Dawson ____________________________________________________________ Learn about VA loan programs and benefits. Click now. http://thirdpartyoffers.juno.com/TGL2141/fc/Ioyw6i3m3mWguucezHInyDvTMZqPNuZVtJ2PrIg6iEz3xSv6sf8Syt/

Thanks all. I reviewed some physics on this, and now it makes sense. Corby, my 5061A is an oldie, it has the early synthesizer that has the UTC offset correction, which I've set to match atomic time (L2095 on the switches). The tube was replaced in '82. So, I need to verify that the C-field current was also adjusted to match the new 76 mGauss setting, right?. Looks like my synthesizer frequency is 12.6317715, so possibly not. This could also explain the 100ps/sec drift wrt my Z3801A. You don't happen to know the proper value for the resistor, do you? Hmm... I wonder if my synthesizer can do ..725 Mhz. I've been toying with the idea of building a new synthesizer using modern a modern digital PLL, going so far as to lay out a PCB for it. Maybe I should follow through on that. Bill Ezell ---------- They said 'Windows or better' so I used Linux. corby d dawson wrote: > The Zeeman frequency is calculated by the amount of C-field current you > use. > > If you change the Zeeman then to get the unit "on frequency" you then > have to change the synthesizer frequency and the C-field current to > compensate. The amount of C-field change is too big for the front panel > knobpot so a resistor change on the A15 board is required. > > The earlier 5061A current (61miiliGauss) resulted in a synthesizer > frequency of 12.6317716 Mhz giving a corresponding Zeeman frequency of > 48.82Khz. > > On later 5061A and B units HP decided that using a different current (76 > milliGauss) that was more stable which ended up giving you 12.7317725Mhz > and 53.53Khz. > > There is NO difference in the tubes C-field winding (for 5061A/B and > 5071A). The current set resistor on the A15 board and the synthesizer > frequency are the only change. > > Corby Dawson > ____________________________________________________________ > Learn about VA loan programs and benefits. Click now. > http://thirdpartyoffers.juno.com/TGL2141/fc/Ioyw6i3m3mWguucezHInyDvTMZqPNuZVtJ2PrIg6iEz3xSv6sf8Syt/ > > _______________________________________________ > 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. > > >