[time-nuts] HP 5061A Problem

paul swed paulswedb at gmail.com
Sat Sep 21 10:35:50 EDT 2013


Adrian
It looks like you are gathering a lot of good detail. I have a couple of
thoughts. But will say there are many on this list that are far far more
knowledgeable then me. My experience was in building a hp 5060/61 combo. A
mixed marriage that worked.
That said. You don't mention the current reading. I understand thats really
relative but would be curious.
So possibilities. The photo multiplier in the tube is actually a tube. They
can go noisey with age. That would be the masking effect that would prevent
2nd harmonic.
To much current may be an additional issue. Lastly the frontend transistors
of the photo mult preamp may be going bad. Just some thoughts.
Regards
Paul.
WB8TSL


On Sat, Sep 21, 2013 at 8:27 AM, Adrian <rfnuts at arcor.de> wrote:

> I got a 5061A with high performance tube that I'm trying to get running.
>
> The Cs oven works and the -3500 and -2500V are there.
> The beam current has its maximum at the correct frequency.
> 90MHz from the multiplier are there and they are phase modulated with
> 137Hz at about 0.01 rad.
> Measured on a spectrum analyzer, the 137Hz sidebands are some -47dBc.
> I'm not sure if that low modulaion index is correct though.
>
> Also, the harmonic generator alignment worked as described in the manual.
> Measured with the EM output into a 10M input DMM, the floor was around
> -60mV, finally set to some -90mV after alignment.
> The low frequency test worked as well and delivered a maximum at some
> 41.6kHz.
>
> An unusual observation is that the meter indicates beam current
> immediately after switching the CBT on.
> Nevertheless, it could be tuned to the correct maximum after warming up.
> However, there is still no 2nd harmonic and it doesn't lock.
>
> Measured with a scope directly at the EM output, there is mainly noise
> with just a faint signal when maxed with the A3 mod level potentiometer.
>
> Unfortunately, I couldn't find reference data in the manual, neither for
> the beam current nor the multiplier modulation index.
>
> So far, everything seems to work properly except for the missing 2nd
> harmonic and the unusual beam curren behavior.
>
> Any help would be much appreciated.
>
> Adrian
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