[time-nuts] HP 5245L Question

[Bob Camp]

Hi

I would be very careful with the reference conversion. 

Your rubidium probably puts out 10 MHz and the counter needs 1 MC ....

The 4000 series CMOS gates probably have quite a bit more jitter than some of the more modern parts. Stuff like the 74AC series will beat them on jitter.

Bob


On Jan 10, 2010, at 11:48 AM, paul swed wrote:

> Arie
> Still working on the a26 board. It works but I want to improve the 10 mc in.
> Most likely a schmitt trigger CD 4093 I might guess. The boards very simple.
> Since I have 10 mc in the shack from a RB standard I simply square it up and
> send it to a CD4050 buffer IC to the 10 MC systems in the 5248M. Then take
> the same 10 MC divide with a CD 4018 to get 1 MC feed this to 3 CD4050
> inverters. I strongly suspect actually one buffer is more then enough in the
> package just have not had time to try it.
> 
> I also found some HP sloppy work. HP no way. But evidently it does happen.
> There is a 7474 on the A35 board that has open set and reset inputs. Good
> practice is to tie those high.
> These are floating and as I had seen with age they become slightly erratic.
> Replaced that chip and will tie the spare leads high.
> 
> I have indeed isolated my issue to the tunnel diode gate section. Inject a
> signal just beyond that and the counter counts. Though incorrectly because
> no gate action.
> 
> I have another 5248 thats been working for years and had never been in it.
> Well I figured I would borrow the A21 card to confirm the issues and measure
> voltages. Son of a gone someone else had the same section issue and cleverly
> replaced the tunnel diode with a ecl 10116. I don't see how they are gating
> that yet. But I do understand how the 10116 works to amplify and clip the
> signal. So I may indeed copy that circuit if I can not recover the gate
> section of A21.
> Regards
> 
> On Sun, Jan 10, 2010 at 11:38 AM, paul swed <paulswedb at gmail.com> wrote:
> 
>> Arie,
>> 
>> 
>> On Sun, Jan 10, 2010 at 7:14 AM, arie schellaars <
>> arie.schellaars at yahoo.com> wrote:
>> 
>>> 
>>> 
>>> 
>>> 
>>> Hi folks,
>>> My 5245L had faulty nixies and my approach was to use Russian replacements
>>> available from a Canadian outfit.
>>> The "snags" are.
>>> These nixies , though a direct socket fit , have a glass extrusion at the
>>> back to
>>> "suck out"  or let in the neon gas during manufacture.
>>> I drilled the socket ,slow and carefully here, to allow this extrusion to
>>> fit into the
>>> socket . There is some room to spare for this on the socket and no
>>> disassembly of the readout card is needed.
>>> The second "snag " is that the figure 5 is in fact an inverted (upside
>>> down) fig 2 but
>>> in practice it's not a problem.
>>> BTW never had a problem with any of the "innards" of the counter boards!
>>> Would be interested in your details of the oscillator board as , like you,
>>> mine came without the crystal. The oven container was there but empty!
>>> Have since obtained a crystal in its oven but still not happy with the A26
>>> board.
>>> performance AND have run out of Germanium transistors as per on that
>>> board.
>>> 
>>> Just had a thought. Ever since I purchased my 5245L many years ago, I have
>>> been on this Time nut treadmill . I guess I should have known better at the
>>> time !!!
>>> Now with a shack full of HP and Tek gear and the inevitable rubidiums ,
>>> GPS thunderbolts and plain old oxco's , time to call "CQ' is at a premium.
>>> (Hi)
>>> Cheers from OZ
>>> Arie
>>> VK3DBF
>>> 
>>> 
>>> Been troubleshooting a 5248 M someone grabbed teh oscilator and A26 board
>>> from it.
>>> The a26 board was replced with 2 cmos chips and 1 transistor.
>>> Now I am at the counter gate. Darned if I don't have an issue in the
>>> dreaded
>>> tunnel diodes area. Such a lucky day for me.
>>> Need to cleanup and solder in the pseudo a26 board so I can more easily
>>> work
>>> on the gate.
>>> 
>>> 
>>> 
>>> 
>>> 
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>> 
>> 
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