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Old 26th Apr 2007, 1:02 pm   #1
Studio263
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Join Date: Apr 2007
Location: Hampshire, UK.
Posts: 1,574
Default FM tuning drift - any ideas?

This is driving me mad! The set in question is a B&O "mini deluxe" (1963) and in the first ten minutes of use it consistently needs about 500KHz of tuning correction to keep it on tune. After this it's OK for as long as it's on.
The set is pretty simple and conventional, it uses an ECC85 for the FM front end, followed by an ECH81, EF89, EBF89 and two Ge diodes for the detector. The FM front end is in a metal box and is capacitively tuned. There is no AFC, an oversight clearly!
I've replaced the usual suspect components on the main chassis and the set works very well otherwise.
The ususal "freezer spray" routine has failled as the ice that forms puts the tuning miles out by itself. I'm also reluctant to go mad and replace everything in the front end as I have heard that some of the capacitors have carefully chose temperatue coefficients.

Any ideas?
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