[time-nuts] Oscillator temperature compensation

[Scott McGrath]

These are not the greatest transmitters high school radio station had something similar.    You might try creating a rudimentary oven for crystal  use a bimetallic switch if you want authentic otherwise transistor circuit to control heater

Did something similar with my Swan 250 years ago.  It was better known as the 'nifty drifty two-fifty'. The oven for vfo system really helped 

Sent from my iPhone

On Jun 21, 2013, at 8:56 AM, Bob Camp <lists at rtty.us> 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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