[time-nuts] HP 5245L Question

[paul swed]

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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>
>