Well, yay... I put the OCXO back in the 5065A, and got a good 2nd Harmonic reading. So I started going through the alignment procedures and somehow I now have no 2nd harmonic again, and I can't get it back...
I'm starting to lose interest in this thing, seeing as I have the Leo Bodnar GPS standard anyway that I don't have to sit for hours twiddling dials and poking things just to get it maybe sort of working. I might give this one more chance before I sell it off to someone with a little more patience, or who prefers fixing gear instead of actually using it. I think I've had this thing working for all of a couple days in the months I've owned it, whereas the GPS standard is the size of a pack of cards and has never failed in the same time. Jared. ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On Thursday, December 2nd, 2021 at 04:19, Bob kb8tq <[email protected]> wrote: > Hi > > The reason for the thermal fuse (which is not a feature of other OCXO’s) > > is the 10811’s deployment in a wide range of devices. There are a few that > > do have restrictions on them. The 5065 is not one of those devices. > > The protection provided is minimal. The pass transistor will fail in a runaway > > situation. Unless you happen to be on a submarine or something similar > > you are not creating a significant problem when it does. > > The thermal fuse significantly degrades the reliability of the device. It is > by > > far the most likely part in the entire OCXO to fail. Putting up with this > failure > > process (and the cost of the fuses) is not reasonable if the benefit is quite > > small. > > Indeed there was some beer involved in the discussion, but HP OCXO > > engineering was onboard with the above information last time we chatted > > about it. That would have been in the early 1990’s …. These failures have > > been going on for a long time. > > Bob > > > On Dec 1, 2021, at 7:41 AM, Wilko Bulte [email protected] wrote: > > > > In general it is a very bad idea to defeat safety provisions that a > > manufacturer put in their product. They are there for a reason, any > > manufacturer would omit them, if only to save on cost. > > > > I would think no-one on this list would replace a blown fuse in their house > > fuse box with a nail. Or? > > > > Wilko > > > > > On 1 Dec 2021, at 12:13, Askild [email protected] wrote: > > > > > > Hi, > > > > > > Just a little warning. > > > > > > Included are some pictures of a 10811 where thermal fuse protection have > > > > > > not functioned. > > > > > > I do not know why, if the fuse did not work, or somebody replaced it with > > > a > > > > > > wire, as this was in a HP 8663A that I found in a recycling bin, and I do > > > > > > not know the history. > > > > > > Regards, > > > > > > Askild > > > > > > > On Tue, Nov 30, 2021 at 8:34 PM Bob kb8tq [email protected] wrote: > > > > > > > > Hi > > > > > > > > The thermal fuses die on their own far more often than they die > > > > protecting > > > > > > > > anything. The fuse is there to provide safety is certain odd situations. > > > > > > > > The > > > > > > > > simple answer these days is to replace it with a piece of wire. > > > > > > > > Bob > > > > > > > > > > On Nov 30, 2021, at 12:05 PM, Larry McDavid [email protected] > > > > > > wrote: > > > > > > > > > > Do these thermal fuses fail spontaneously or is there a common cause? > > > > > > > > > > If the "heater" transistor mounting screws were quite loose, those > > > > > > > > > > transistors themselves might have overheated and failed. But, a > > > > > thermal > > > > > > > > > > fuse should fail by high temperature... > > > > > > > > > > Sounds like progress, though. Cold OCXO means low frequency. > > > > > > > > > > Jared, I sent you a private email with some pictures; did you get > > > > > that? > > > > > > > > > > Larry > > > > > > > > > > On 11/30/2021 8:03 AM, Jared Cabot via time-nuts wrote: > > > > > > > > > > > Well, I found it, the thermal fuse is open circuit. > > > > > > > > > > > > If I briefly bypass it with a jumper wire, the oven pulls the > > > > > > expected > > > > > > > > > > > > current. > > > > > > > > > > > Looks like I need something that will trip at roughly around 115C, > > > > > > > > > > > > rated to 1.0A > > > > > > > > > > > (HP Part number 10811-80008) > > > > > > > > > > > > Hopefully I can find something in Akihabara to make it easier to > > > > > > get my > > > > > > > > > > > > hands on ASAP... > > > > > > > > > > > Jared > > > > > > > > > > > > ... > > > > > > > > > > > > -- > > > > > > > > > > > > Best wishes, > > > > > > > > > > Larry McDavid W6FUB > > > > > > > > > > Anaheim, California (SE of Los Angeles, near Disneyland) > > > > > > > > > > time-nuts mailing list -- [email protected] -- To unsubscribe > > > > > > > > > > send an email to [email protected] > > > > > > > > > > To unsubscribe, go to and follow the instructions there. > > > > > > > > time-nuts mailing list -- [email protected] -- To unsubscribe > > > > send > > > > > > > > an email to [email protected] > > > > > > > > To unsubscribe, go to and follow the instructions there. > > > > <P1010309_s.jpg><P1010305_s.jpg><P1010306_s.jpg> > > > > > time-nuts mailing list -- [email protected] -- To unsubscribe send > > > an email to [email protected] > > > > > > To unsubscribe, go to and follow the instructions there. > > > > time-nuts mailing list -- [email protected] -- To unsubscribe send > > an email to [email protected] > > > > To unsubscribe, go to and follow the instructions there. > > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > > To unsubscribe, go to and follow the instructions there.
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