[time-nuts] Oscillator temperature compensation

[Brian Alsop]

"Drift quite a bit" is a matter of what century you are in.

Don't forget in this era, fine calibration marks on most receivers were 
5 KC, if you were lucky.  They would drift only 20 KHz/hour, if you were 
lucky.  Receiver bandwidths were 10 KC.  Drifting 1 KC on AM transmit 
would hardly be noticed.

On CW, you'd have to find the station in the RX you were talking to 
after a brief period of transmit.  The station drifted out of the 
receiver pass band in the 40 or so seconds of transmit.

Things have changed.  I sent back a radio master oscillator that was 
supposed to drift only +/- 5Hz per day because it had a range of +/-15 Hz.

Regards,
Brian

On 6/21/2013 12:56, Bob Camp wrote:
> Hi
>
> At that frequency, the crystal is likely some sort of bar cut rather than an AT. If the transmitter has no oven / heater around the crystal, it will indeed drift quite a bit.
>
> Bob
>
> On Jun 21, 2013, at 12:09 AM, Joseph Gray <jgray at zianet.com> wrote:
>
>> This is not strictly Time Nuts, but it is about a crystal oscillator that
>> needs some temperature compensation, or something. Please ignore this
>> posting if you like. In fact, so as not to clutter up the list, it would be
>> best to email me directly about this.
>>
>> I have an old AM transmitter that has three 6AL11 compactrons. The crystal
>> is a fundamental, cut for 660 KHz. I don't have a schematic for this thing,
>> but I believe that one half of one 6AL11 is used for the oscillator.
>>
>> The problem is, the frequency decreases as the rig warms up. It will
>> eventually stabilize, but the final frequency is over 200 Hz low. Not as
>> good as it should be. I think the original specification was well under
>> half of that.
>>
>> I have replaced the electrolytic caps. The others are mostly silver/mica
>> with a few ceramics. I checked all of the resistors and only found one that
>> was out of tolerance (I replaced it).Three NOS tubes were installed. There
>> are no tunable components in the oscillator section. Only the output
>> section has anything tunable.
>>
>> I know that there are many Amateurs on the list and I'm sure many know more
>> about old tube rigs than I do. Does anyone have a suggestion as to what the
>> trouble might be?
>>
>> Joe Gray
>> W5JG
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