[time-nuts] Re: HP 5065A, no 2nd harmonic.

[Magnus Danielson]

Hi Jared,

One of my 5065's have exactly this fault.

One approach is to rebuild with a new power inverter. Another is to 
rebuild the amplifier board so it does not need -20 V and can operate 
only on +20 V.

There should be DC-DC inverters, but I failed to grab a suitable 
pre-built board for it.

I would enjoy not having to hear the 3.5 kHz switching frequency in my lab.

Cheers,
Magnus

Den 2021-12-02 kl. 15:15, skrev Jared Cabot via time-nuts:
> So it looks like I lost the -20V rail. Seems that A15Q10 (2N4234), A10CR9A (9V Zener), and A15CR9B (11V Zener) are all dead for some reason.
> Q10 is easy enought o find, but the zeners are a little more tricky, they are specified as part number 1902-0247, a 20V, 1%, 0.4W +0.005%TC zener (20V made up of the 9v + 11V).
> I can find a 5% 9V (1N936A), but the 11V is harder to find.
>
> Maybe I should look into redesigning this board entirely, the transformer on mine is rather noisy anyway.....
>
> Schematics attached for reference.
>
>
>
> Jared
>
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
>
> On Thursday, December 2nd, 2021 at 21:04, Jared Cabot <jaredcabot at protonmail.com> wrote:
>
>> Latest update.
>>
>> Looks like I'm getting 2.76VDC out of A7J1 and I can't adjust it with A7R3. According to the manual, it should be less than 50mV.. I was able to set this to around 0.5mV previously, so it did work at one point.
>>
>> Q1 and Q2 test ok on my ebay component tester, IC1 is a selected uA741TC, but I'm not sure how to effectively test it.
>>
>> (I attached the schematic, hopefully it shows up ok).
>>
>> Jared
>>
>> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
>>
>> On Thursday, December 2nd, 2021 at 18:57, Jared Cabot via time-nuts time-nuts at lists.febo.com wrote:
>>
>>> Well, it seems more digging is needed... I have 84uA Photo I coming from the RVFR on A7P1, but the front panel is at 14 (Should be 42 for my Photo I level)
>>>
>>> Manual says look at Q1, Q2 and IC1 circuits. Anyone have any pointers or suggestions on what to check?
>>>
>>> Jared.
>>>
>>> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
>>>
>>> On Thursday, December 2nd, 2021 at 17:21, Andy Gardner, ZL3AG via time-nuts time-nuts at lists.febo.com wrote:
>>>
>>>> Don't give up now, Jared! You must be so close to getting that puppy running correctly.
>>>> On 2/12/21 9:16 pm, Jared Cabot via time-nuts wrote:
>>>>> 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.
>>>> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an email to time-nuts-leave at lists.febo.com
>>>> To unsubscribe, go to and follow the instructions there._______________________________________________
>>> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an email to time-nuts-leave at lists.febo.com
>>>
>>> To unsubscribe, go to and follow the instructions there.
>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an email to time-nuts-leave at lists.febo.com
>>> To unsubscribe, go to and follow the instructions there.