[time-nuts] HP5071A with bad tube.... can I get one used?

[Bob kb8tq]

Hi

Based on running a high performance tube version of the 5071A for a number of years, the
tubes last about 5 to 7 years when run 24/7/365. Once they die, the practical ($$$$$$$)
alternative is to send the beast back to the factory for a new tube. Indeed given the price
and the complexity of shipping (it’s a hazmat item), this is only practical if you are a company
that needs to use the device. 

At least on the high performance 5071, the “end of life” process is not an immediate death sort of
thing. The stability (ADEV) of the device degrades as the tube wears out. If you have a stability 
requirement (not just function) the wear out point will be a bit earlier than the numbers above.
Just how much earlier depends a bit on how picky you are. ( = if you high performance tube is 
worse than a standard tube, how happy are you?) You also would need the gear to test the ADEV. 

Some of what’s in the 5071A is running based on firmware and settings shot in here and there
on the device. Updating / adjusting / tweaking those settings has not been documented out
here “in the wild” AFIK. The factory (obviously) does understand how to tweak this or that. 
The degree to which tweaks might be needed with this or that unusual tube is very much 
open to debate.

The whole “can’t get a tube” issue is hardly unique to the 5071A. I have a pair of Cs standards
in the basement. Both have tube issues. One may be repairable if I ever get around to playing
with the fix. Once “fixed” will it run for another few months or a few more years? There is no way
to know without trying it. 

Will this or that tube last a month, a year or two or a decade or thee? I know of no external test that will
guarantee a decade of capacity. There are indeed tests that will suggest that you are limping along. 
Most (but not all) basement Cs standards are in the “limping along” category. As with the 5071, 
just what constitutes limping along, depends a bit on how close to (or how much better than) the 
factory spec you need to be.

Bob

> On Oct 23, 2019, at 11:42 PM, Taka Kamiya via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> I have an HP5071A with a high performance option that does not work.  All of my tests indicate the faulty component is a tube itself.  Buying a new tube is way out of my budget.  I am now torn between parting it out and see what I can use and keeping it intact with hope something might pop up.  
> 
> Question for the group....  Obtaining a used tube for this, I don't care if its high performance or not, as long as it works with the chassis, is really not a possibility, correct?  I have never seen one on eBay.
> 
> --------------------------------------- 
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
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