I have been studying up on paraphase inverters, as it is something I have not built in any amp projects so far & I thought I might try to include one in a future project.
Looking through schematics of the usual suspects, I have noticed that most designs have the voltage divider feeding the second grid located after the coupling caps going to the power tubes, & the divider then doubles as the grid leaks for the power tubes.
The exception seems to be Ampeg whose designs have the divider located on the PI-side of the coupling caps, & have a second set of dedicated grid leaks on the power tube-side of the coupling caps.
I am wondering if this is purely down to parts count or if there is more nuance to it than that?
Fender
Benson
Gibson
Ampeg
Ampeg
Paraphase Inverter Voltage Divider Placement
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Paraphase Inverter Voltage Divider Placement
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Re: Paraphase Inverter Voltage Divider Placement
Ampeg used floating paraphase which is a bit different from the other examples. Also the second Ampeg example is fixed bias where the coupling cap and gird leak resistor to the second half of the phase inverter are necessary. The reason why the divider is located on the PI side of the coupling caps is so that there's only one RC frequency roll off to the second grid of the PI.
Re: Paraphase Inverter Voltage Divider Placement
Thank you for pointing that out, I hadn't even considered that.
That 2nd Ampeg example had switchable cathode/fixed bias as it was a reissue circuit combining two versions of the B-15. Probably not the best example, but it was in hand.