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Dyna FM-3 Problem

Before I dig into this I wanted to see if others have experienced the same thing.

On most of the FM-3's I've owned, After going through and aligning them a problem remains. When tuning across the dial, I experience a severe, what can best be described as "growling" or a "staticky sound" when tuning through strong stations. It's NOT a tuning capacitor problem - i.e. noisy bearing or shorting variable cap sections. I believe it is actually what is called "IF regeneration" - too much gain in the IF section which when a strong input signal comes along, causes the whole section to oscillate which you hear as what used to be called "blocking".

I've experienced this many other tubed tuners including various Scotts and McIntoshes. A way around this in certain units it is to actually "detune" the IF section slightly (trading off gain for wider bandwidth) BUT most of these others have some king of Automatic Gain Control where there is none in the Dyna. The first two IF amps are run "wide open" and I think this may be contributing to the problem.

"Shortly", I hope to tackle it by playing with (reducing slightly??) the IF gain structure and/or perhaps adding a manual RF gain control if necessary.

So after a long-winded narrative - any of you'se FM-3bee's experience anything similar?

Charles


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Topic - Dyna FM-3 Problem - stellavox 05:07:03 01/14/10 (2)

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