[time-nuts] HP5061B Peak to Valley Ratios
https://www.febo.com/pipermail/time-nuts/2017-April/104600.html We did our first Zeeman frequency test on our good cesium 05061-6077 Tube with a 1 Meg scope probe and a 11 Meg Digital Voltmeter in parallel. KB7APQ used his digital generator for the variable frequency. See paragraph 3-16 on page 3-8. At 53.53 kc the level peaked at 3 V peak to peak which is close to the theoretical 1 V rms. I didn't have a program readily available to do a graph but you can see the main and upper and lower adjacent peaks. We can compare with Figure 4-43 (page 4-31) in the service manual for the HP5061B if anyone can graph this. We had the C field control at the factory setting of 453. Our actual maximum on main peak was 53.657 kc not 53.530 kc. We got 53.530 kc with a slightly different new C field setting of 463. Factor spec is within 100 cps and we were 127 cps off. This is probably not a bad drift for a 30 year old instrument. https://www.febo.com/pipermail/time-nuts/2017-April/104600.html kc beam (C Field set at 453) 55.03 27 54.93 27 54.83 27 54.73 28 54.63 30 54.53 32 54.43 33 54.33 31 54.23 28 54.13 25 54.03 22 53.93 22 53.83 24 53.73 29 53.63 35 53.53 32 53.43 39 53.33 34 53.23 28 53.13 24 53.03 22 52.93 23 52.83 25 52.73 28 52.63 31 52.53 32 52.43 31 52.33 29 52.23 27 52.13 27 52.03 26 We suspect a bad beam tube on our second instrument and therefore wanted to practice the Low Frequency Coil test on our known good beam tube. It allows the performance of the tube to be checked with no rf drive. See paragraph 5-175 (page 5-22) We used 26.765 kc and it also peaked out at 3 V pp. I discovered that this is half of the Zeeman frequency but it is not clear why this is so. We obtained a beam current of 23 with rf drive removed from the tube by pulling P2 on A4A1. I spoke to Corby Dawson last night. Among many things, he reported that you will be able to get 80% to 90% of this beam current in normal lock mode. We are getting 87% or 20. πθ°μΩω±√·Γλ WB0KVV ___ 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] HP5061B Peak to Valley Ratios
https://www.febo.com/pipermail/time-nuts/2017-April/104600.html We hooked up the oscilloscope directly to the electron multiplier in the beam tube with a 1 Meg termination. We were operating open loop and varying the fine crystal oscillator adjust for the different photos. Remember that higher beam current is downward in the photo. Currents listed in nA translate to beam current numbers on the HP5061B meter. First photo at http://gonascent.com/papers/hp/hp5061/waveform/centered.jpg is the frequency swept at a 137 cps rate around the peak of the cesium resonance. Ground is at the top of the screen and 5 mV (also 5 nA) per division. Horizonal is 4 ms per division.This corresponds to a peak beam current of -22 nA and a valley current of -17 nA. One valley current is below resonance and the other is above resonance. The waveform is 274 cps. Sequence is low to high and then high to low. No 137 cps is present. The fine frequency control was adjusted to produce a slight offset from center for the photo at http://gonascent.com/papers/hp/hp5061/waveform/smalloff.jpg . Note that the peak beam current is still -22 nA but two different valley currents exist. One is 17 nA and the other is -18 nA. Most of the signal is 274 cps but some asymmetry is present at 137 cps. One extreme of the sweep is slightly closer to center frequency than the other. Finally the frequency was adjusted to produce a severe offset with all of the sweep below resonance in the photo of http://gonascent.com/papers/hp/hp5061/waveform/largeoff.jpg . The peak is now slightly below resonance at -21 nA and the valley is far below resonance at 5 nA. The signal is all 137 cps with no 274 cps. See figures 4-43 and 4-44 on page 4-31 of the manual for further explanation. We will be finding out the effect on beam current of tests shortly on the Zeeman coil and LF coil. We think that the 55.53 kc Zeeman frequency introduces some AM into the beam frequency but no FM. What the LF coil has is unclear at this time. πθ°μΩω±√·Γλ WB0KVV ___ 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] HP5061B Peak to Valley Ratios
Donald, I agree with John, remove the gearing gizmo from the 10811 assy. the adjust hole lines up any way so no need to drill a hole. you just need a long insulated tuning tool. Also agree that a quick indication of tube operation can be seen if the beam current rises when the mod is turned off. The Cesium tube test, set seen in http://leapsecond.com/corby/HP-5071A-with-5061A-4.docx is essentially a stand alone low frequency coil test. If I can't get a decent LF coil beam current I scrap the tube as it's a waste of time to put in in a unit and try the RF tests. The test set uses a 555 based oscillator. For low frequency tests in an instrument I use a 651B or 204C. Set the amplitude and frequency for a peak on the beam current, make sure mod is off and that you are on the central peak. The figure of merit test in the manual will give an indication of how well the tube and instrument are working, but a definitive test is to perform an Allan deviation of the unit. Cheers, Corby ___ 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.
Re: [time-nuts] HP5061B Peak to Valley Ratios
> We are having trouble getting beam current on our #2 HP5061B. Ion > current has gone down in a week from 10 to zero. It looks like the rf > chain is working normally. Both HV power supplies had to repaired. > Beam current is all the way up and which gives 2 on the meter. We are > preparing to do the Low Frequency Coil test mentioned on page 5-22 > section 5-175. > > I got this idea from that procedure. On our good #1 instrument we set > the beam current at 20 with normal lock. The middle coax J2 which > carries 12.631 mc to the harmonic generator was removed next. The > beam current instantly dropped to 2. We set the beam current with the > front panel control at 10 to 30 and all three settings dropped about > 10 to one when the cable was pulled. This ratio seems to be a good > indicator of beam tube quality. Other useful cues are the effect on the beam current when you turn the modulation off -- it should rise a bit -- and the stability of the meter needle in the beam-current position as an indicator of tube noise. In that regard, excess noise from A13CR1 could potentially be mistaken for noise in the tube itself. It could stand a bit more bypassing IMHO. > I don't see it in the manual, but the > fine five turn pot oscillator control works much better than the > course adjustment for setting peak beam current. It also works better > for setting the control voltage to zero. The push to turn course > frequency control slot has been chewed up by the previous owner. It's a good idea to remove that contraption altogether. You don't want anything poking into the 10811's trimmer access hole or otherwise touching it. Drill a hole in the panel that will let you reach the 10811's trimmer directly with an alignment tool. It will then be easy to follow the guidelines in the manual -- i.e., set the OCXO trimmer to the central peak with the pot at 250. The intent was probably to achieve a consistent operating point at a linear spot in the EFC curve, while discouraging technicians from setting the 5-turn pot near either extreme. By specifying a midscale setting for the pot, they were able to maintain a consistent damping factor between units while incidentally making it easier to return to the central peak after any temporary adjustments. The 10811-60109s are all labeled with a factory-selected resistor value for the same reason. Overkill, but that's how HP rolled. -- john, KE5FX Miles Design LLC ___ 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] HP5061B Peak to Valley Ratios
We are having trouble getting beam current on our #2 HP5061B. Ion current has gone down in a week from 10 to zero. It looks like the rf chain is working normally. Both HV power supplies had to repaired. Beam current is all the way up and which gives 2 on the meter. We are preparing to do the Low Frequency Coil test mentioned on page 5-22 section 5-175. I got this idea from that procedure. On our good #1 instrument we set the beam current at 20 with normal lock. The middle coax J2 which carries 12.631 mc to the harmonic generator was removed next. The beam current instantly dropped to 2. We set the beam current with the front panel control at 10 to 30 and all three settings dropped about 10 to one when the cable was pulled. This ratio seems to be a good indicator of beam tube quality. I don't see it in the manual, but the fine five turn pot oscillator control works much better than the course adjustment for setting peak beam current. It also works better for setting the control voltage to zero. The push to turn course frequency control slot has been chewed up by the previous owner. We are planning to get an oscilloscope display of the main and secondary lobes similar to page 4-31 Figure 4-43. If it works we will post it. It should show both the dc and ac parts of the beam current as the 137 cps sweep goes from one extreme to the other. Will anyone having any experience with the Low Frequency Coil test kindly post on the subject? This is NOT the Zeeman frequency test. ___ 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.
