Frequency stability of an HP3310A function generator

[KJDS]

I've just been asked what the stability is like for an old analogue HP3310A function generator that I've sold so thought I'd run some tests this evening.

I let it warm up, set it to 100kHz and it measured 100.454kHz.

I'll keep the thread updated to report how it drifts.

[KJDS]

It's now at 100.366kHz

[Yago]

How are you measuring it?
Just guessing here, but interested, I imagine a counter would have drift too.

[KJDS]

How are you measuring it?
Just guessing here, but interested, I imagine a counter would have drift too.

I'm using a Keithley 2015THD, which has a not very accurate frequency reference, but it's likely to be way better than the HP3310A.

It's now at 100.365kHz and I'm off to find a better counter as I've just seen that the ancient HP box is far more stable than expected.

[Yago]

Oh to even have the choice!

[KJDS]

It's now reading 100.360 on the Keithley and 100.359 on a HP5334B

[Yago]

That's just showing off now Kev

[KJDS]

They've both settled down to 100.355kHz

Given that the Keithley freq spec is only 0.01% and its not been calibrated in years it's doing well

[KJDS]

100.349

I'm amazed at just how stable this is

[Yago]

Tell you what, it's better than formula 1 this!  

[KJDS]

100.352

Time for bed, so that's all folks.

[Yago]

Cya later KJDS.

If you get time tomorrow, could you explain what we should look for when evaluating a gen like this?
What might be obvious, may not be so to the likes of me!

Cheers

[Dave92F1]

It's now at 100.365kHz and I'm off to find a better counter as I've just seen that the ancient HP box is far more stable than expected.

I have a HP 3312A that is very _un_stable in frequency. Frequency drops about 20% over the course of two hours (even after warming up before starting), and doesn't really settle down even after 6 hours.  I wish I knew where to start looking for the problem...

[Paul Moir]

The 3312A just has a simple VCO controlling it's frequency.  Have a look at figure 7-5 in the manual, bottom or left hand side depending on which way you're looking at it.  Either it's one of the power supplies drifting (17, 14 and -14), the VCO input, something coming in from the modulation generator or one of the half-dozen components that make up the VCO.
Let me know if there's any specific measurements you want made.