Aha! That is very interesting background information! It nicely puts your comment in perspective to "bridge the fuse with a wire and be done with it".
Big grin here when reading the "beer was involved" comment. I have used a similar approach on my business visits to HP CXO (well after T&M was spun off) ;-). A bit like a certain "beer ware license" (hi Poul). Wilko > On 1 Dec 2021, at 20:20, 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. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
