[time-nuts] Looking for HP105B addendum for HP11801 oscillator upgrade

[gandalfg8 at aol.com]

I have experienced a similar issue with the later 105B "oven" metering and know of at least one other that also behaves similarly.The "oven" meter reading depands on the output from the so called "24 Volt" regulator.The 1973 prefix 1240A manual states that for the 105A the output from the 24 Volt regulator should be between 28 and 32 Volts but for the 105B should be between 26 and 28 Volts. The "problem" 105B had a power supply board that matched the schematic in that manual and the 24 Volt regulator is shown as non adjustable and referenced to a 32 Volt Zener diode and that was what was coming out of it.Having established that the oven was performing as it should be the "24 Volt" supply voltage was reduced by swapping the 32 Volt zener for 29 Volts and the metering problem was resolved and has remained so for several years, now reading 85 on the 0 to 100 meter scale when the oven has warmed up.There were also problems with the 18.7 Volt regulator, which defied all efforts to persuade it to regulate properly, and that was eventually rebuilt to the same schematic as the 24 Volts supply, obviously with the appropriate Zener voltage:-), and that too continues to be ok.Given the specified voltage for the 105B I'm not sure if the Zener voltage should have been lower in the 24 Volt supply anyway, although I don't recall seeing any schematic that suggests that, so I'm not sure if the PSU card had been swapped out at some time.In the prefix 2848A updates that Charles linked to there is also an updated supply based on three terminal regulators but I've not come across one of those.I haven't experienced any stability issues with the 105B so can't really comment on that, but if it were mine I'd be inclined to run it from some known good bench supplies in the first instance and see how it behaves then.Nigel GM8PZR
I have an HP105B with a newerHP11801 oscillator.  When switching toOVEN position, meter goes to full scale and stays there forever.  It has been over a week this way.  Also, the frequency is unstable.  According to archive, this particular updatewas never a part of the main manual but was covered in separate 1/2" thickyellow booklet.  Does anyone have asoft-copy of this?All I found in archive was"contact me via DM" and was over 15 years ago. ---------------------------------------(Mr.) Taka KamiyaKB4EMF / ex JF2DKG