acec: about the ACEC5821 Schematic

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Forum » Radios, TV, Appareils techniques (Physique) etc. » MODÈLES PRÉSENTÉS » acec: about the ACEC5821 Schematic
Yves Barbin
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11.Sep.18 22:55

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I found two probable lacks in the schematic available on the Radiomuseum site for the ACEC 5821

1/ On the first page, on the FM tuner, for the second triode, the oscillator,

the primary coil of the tuned coupling transformer fed by the anode through the 8.2pf needs to be grounded

at the other terminal

otherwise nothing is feeding the feed back circuit and there will be no oscillation, at least no tuned oscillation.

2/ On the second page, in the AGC loop, I think that the low pass filtering capacitor is missing.

The two grids, the one of the heptode ECH81 and the one of the pentode EF89 received the AGC without low pass (which is normally smoothing the gain command). This lack may also introduce a AC coupling beetween the two stages.

There may be some bad consequences.

So according with the 1.8Mohms, a capacitor of 47nF or 0.1uF should be connected to the ground.

This is a very common, very convenient  and  safe practice

What do you think?

Best regards