[time-nuts] HP 106B quartz frequency standard...the story so, far

[Bruce Griffiths]

The 18V regulator is still not directly replaceable with an LT1581 which
has an inadequate voltage rating.
Replacing either of the 2N1701's with a more modern transistor may well
lead to oscillations due to the much higher ft of the replacement
transistor.

Bruce

Adrian wrote:
> Re-read Jim's posts.
>
> To me it seems clear that he is talking about the 2N1701 Q3 in the
> upper right corner of fig. 5-12.
> He mentioned that +18 measures high, around 26V.
> So, the problem is NOT in the battery charger circuit.
>
> The purpose of that Q3 is to generate +17.4V (and +7V) from +26V, with
> the base being connected to +18V, thus the emitter voltage of Q3 is
> +18V - 0.6 to - 0.7V.
>
> The +18V regulator circuit is on the lower left of fig 5-8, A1A4 Outer
> Oven Controller. For a circuit description see 4-40 to 4-44.
>
> The +18V feed the AC amplifier (A1A2), the +15V through R14 (might be
> cooked if run at 26V for extended time) and CR2 on the same board, the
> power amplifier (A1A3), the outer oven temperature control circuit
> (decoupled +18V), and the inner oven control cuircuit A1A5.
> The 17.4V that are derived from +18V feed the dividers.
>
> Any adjustments make sense only after fixing the +18V supply.
>
> Actually, Q3 might as well be shorted. I would first remove it from
> the circuit to see if the +18V are then correct.
> If not, check the voltages at Q9 and Q7 of A1A4. Q9 is mounted on the
> oven housing cover.
>
> Regards,
> Adrian
>
> Bruce Griffiths schrieb:
>> christopher hoover wrote:
>>  
>>>>  The 2N1701 is a general purpose transistor rated at 60V, 2.5A.
>>>>       
>>> I've mentioned this before, but it bears repeating.
>>>
>>> If you are having trouble with an old school linear power supply, in
>>> many cases you can replace the TO-220 PNP pass transistor *and* the
>>> reguatlor circuit (based on a 723 or whatever) with a modern
>>> integrated regulator in TO-220 such as an LT1581.  Strip the regular
>>> board of everything except for the the input and output caps (if they
>>> are still good) and wire up a pair of resistors to set the voltage. 
>>> Add a couple of jumpers to complete the circuit.   And then you are
>>> good to go.
>>>
>>> -ch
>>>
>>>     
>> That probably wont work in this case.
>> The supply is actually an NPN discrete darlington buffered 32V zener
>> with a current limit transistor to set the battery charging current to
>> one of 2 values.
>> With the battery removed the supply output should rise to 32V - 2Vbe - a
>> diode drop, ie about 29.8V or so.
>> The series diode is required to isolate the battery from the regulator
>> output when the main fails.
>> It should be much quicker and easier to just find suitable transistors.
>>
>> Bruce
>>
>>
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>
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