[time-nuts] Oscillator temperature compensation

[Bob Camp]

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
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.