phase inverter question - Printable Version

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+--- Thread: phase inverter question (/showthread.php?tid=21445)

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phase inverter question - pokey - 06-28-2020

As I continue my first journey through capacitor replacement (4 done so far!), I'm learning about the various circuits.  

Would the Phorum wisdom please help me understand the paths in and out of this 7AF7 (46-1209)?  I think ...

... audio comes into the left-side grid (pin 4); it goes out the left-side cathode (pin 2) and, inverted, out the left-side plate (pin 3); these go into their respective 6V6s.

Am I on the right track?

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RE: phase inverter question - RodB - 06-28-2020

Yes, you are correct. This type of phase inverter is a cathode follower. The plate load resistor and the cathode resistor are close in value so the signal level will be almost the same. This circuit will be very sensitive to age related drifting of the 2 resistors.

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RE: phase inverter question - pokey - 06-28-2020

Woo-hoo! Thank you, Rod.

Just to confirm: the two resistors in question are 86 and 87? They measure 372k and 439k. Should I replace them?

Does the right-side triode handle the phono signal? If so, does it also do the phase inversion dance?

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RE: phase inverter question - RodB - 06-28-2020

The resistors in the phase inverter are 78+79 and 80. The right side triode is a preamp for the phono Input. It's output runs off the diagram, probably to a mode switch then feeds the phase inverter.

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RE: phase inverter question - RodB - 06-28-2020

Yes, replace 86 and 87, they are way out of tolerance.

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RE: phase inverter question - pokey - 06-28-2020

Many thanks!!

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