Phase inverter with EF86

[Leevi]

I have a need to invert phase in a EF86 preamp.


Are there some good practices to do that without increasing the amplification?


The available resources for that are 1/2 12AX7 and EF86.


/Leevi

[kagliostro]

Use the triode as CF

it will invert the signal in exit from the ef86

Franco

[Leevi]

Hi Franco, do you have an example?IMO cathode follower does not invert the phase.
/Leevi

[Leevi]

This works
/Leevi

[kagliostro]

My fault, you are right

however you can solve with the same triode, arrange an anode follower with 1 or less of gain (if you don't want it)

may be you can have the same result using a mosfet instead of to add a triode

Franco

[astronomicum]

I have a need to invert phase in a EF86 preamp.
Are there some good practices to do that without increasing the amplification?
The available resources for that are 1/2 12AX7 and EF86.
/Leevi

The Univox U-1221 uses a cathodyne (unity gain) after the pentode in the PI position. They used a 6AN8. May provide an option.

[kagliostro]

If I've understand correctly Levi want only to invert the signal, not to have a phase inverter to drive a PP Power section

However using one of the exit of a concertina can give the wanted result

Franco

[sluckey]

This works
/Leevi

Yes. The cathodyne is the simplest way to get inversion with no gain. Ignore the cathode output. You could replace the plate resistor with a pot if it's important to adjust the gain to exactly 1.

[Williamblake]

You could use a signal output transformer with enough connections, it would give you any phase you want and also provide galvanic isolation which might be a very nice thing to have in a preamp.

[Leevi]

If I've understand correctly Levi want only to invert the signal, not to have a phase inverter to drive a PP Power section

Yes, I'm going switch two preamp channels together and I want that the signals are in same phase.

EDIT: A common input is used for both channels  (A and B) and you can switch between  A, B and A+B

/Leevi

[isaac_teller]

https://www.zupimages.net/viewer.php?id=20/06/y6u6.png


Not an EF86 but similar implementation.
https://schematicheaven.net/bargainbin/dano_special.pdf