[time-nuts] HP10811 losing EFC

[Tom Holmes, N8ZM]

While on the subject of 10811's, I have one which appears to have a blown
fuse. Bypassing same, it seems to work OK, so suspect that tiny filament or
whatever simply succumbed to some shock or vibration, or maybe just old age.
I don't recall the current draw now, but it seemed reasonable at the time,
and it came up on frequency and appeared to be controlling the oven temp OK.


Would like to replace the fuse with something more correct than a #22 before
I let it go online full time. 

Any ideas for where to get replacement, or a suitable substitute?

Thanks. This is a fun list to monitor. I learn more in a day here than
anything else I've ever done.

Regards,

Tom Holmes, N8ZM
Tipp City, OH
EM79xx

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Rick Karlquist
Sent: Friday, January 15, 2010 7:54 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] HP10811 losing EFC

No one has mentioned the fact that the cathode of the varactor
is connected to an internal 6.8V Zener diode voltage reference.
This is another source of trouble.

Rick Karlquist
N6RK


Bob Camp wrote:
> Hi
>
> I sure would do some quick continuity checks on the EFC line before I
> started swapping varicaps out. A bum solder joint opening up is a lot more
> likely than the varicap going nuts in a fashion that still lets the
> oscillator run.
>
> Bob
>
>
> On Jan 15, 2010, at 7:08 PM, Neville Michie wrote:
>
>> Hi,
>>
>> I have two HP10811 oscillators that do not respond to EFC voltage.
>> The latest to fail had been quite accurately set against a TBOLT,
>> one morning (after being on standby in a HP5328A) it was off frequency
>> and would not shift with EFC but would adjust with the coarse adjust.
>> I have bought in two Phillips varicap diodes, BBY40 and BB149A,
>> but before I did some damage fault finding in the HP10811s  I thought
>> it wise to ask for any advice that was available.
>> While I am playing with them I may try to readjust the temperature
>> setting
>> of the oven to get on top of the turnover. Can anyone point me to that
>> article?
>>
>> cheers, Neville Michie
>>
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