Talking of OXCO's I've been putting one of my HP 10811Ds into a case and fired it up for the first time on Tuesday. Frequency was fine with No EFC and the mechanical trimmer untouched since it was removed ftom a 8922 cell test set abou 4 years ago and has been in a storae container for at least a couple of years the error to GPS was 0.052Hz.
Overall I'm pretty pleased. I made one difficult decision to use a DC-DC converter so it can run off mains or 9-18V DC. I'm seeing a little bit of nise from the DC-DC on the output. It goes up with the oven current and appears to be short bursts of noise. It's good enough as a frequency reference but not to multiply up to microwavs frequencies. I'll have to do a bit of work and see if I can knock it down a bit further.
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1209058)
Almost looks like the case was once from a hp 220/221A, I hope I'm wrong.
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1209180)
David
You are not wrong, it used to be a 221A
However, in my defence, It was one of two that I rescued from from being scrapped. That one had very worn controls and switches. It was always tempermental and last time I powered it on it let the magic smoke out ![Broken! :-BROKE](https://www.eevblog.com/forum/Smileys/default/smiliey_scope_broke.gif)
The second one was repaired and is used everyso often but they are not a great generator, completly uncalibrated.
To prevent these little guys form eradication I've just rescued one from the bay as the only bidder for 25 Euros :-)
In 1972 HP catalogue it was probably the lowest cost device with 240$. Definitely the smallest in the pulse generator range, reaching up to a 8008A for 2,700$.
This one got some repairs obviously and is working. Max frequency is some 8 Mhz and at 1Mhz the function looks kind of square.
You've beat me to posting pictures of mine, ended up very tired & knackered after my first week back at work since last year.
![Indifferent :=\](https://www.eevblog.com/forum/Smileys/default/indifferent0023.gif.pagespeed.ce.nyXMDasYXd.gif)
Haven't seen one listed in the UK for years, ended up buying my 221A last month from a US seller.
There does seem to be a lack of any manuals (real or pdf) available though, maybe that was why Robert murdered his.
![Cry :'(](https://www.eevblog.com/forum/Smileys/default/xcry.gif.pagespeed.ic.tehjCtKixU.png)
Need to find the 220A to go with it too.
Letting the smoke out is a feature of HP generators around that era. Also gratuitous annoying use of tunnel diodes and unobtainium hybrid ASICs
I'm not seeing any tunnel diodes or ASICs unless my eyesight needs testing, this is a 1960's design by the way, supposed to be good for 10MHz.
David