Ihave a Philco model 20 with an open primary in the output transformer. Does anyone know what impedance is needed for the 71A's in push pull configuration and if a universal output transformer will work?

: Ihave a Philco model 20 with an open primary in the output transformer. Does anyone know what impedance is needed for the 71A's in push pull configuration and if a universal output transformer will work?

Sure, it can't be that critical. Who knows what the speaker impedance is anyway? Try it and see.

I have a Popular Electronics article on how to wind your own output transformers scanned in.
If anybody is interested, email me. Denis

:
: : Ihave a Philco model 20 with an open primary in the output transformer. Does anyone know what impedance is needed for the 71A's in push pull configuration and if a universal output transformer will work?

: Sure, it can't be that critical. Who knows what the speaker impedance is anyway? Try it and see.

:I have a Popular Electronics article on how to wind your own output transformers scanned in.
:If anybody is interested, email me. Denis
:
::
:: : Ihave a Philco model 20 with an open primary in the output transformer. Does anyone know what impedance is needed for the 71A's in push pull configuration and if a universal output transformer will work?
:
:: Sure, it can't be that critical. Who knows what the speaker impedance is anyway? Try it and see.
:
:Denis: How can I get a copy of the Popular Electronics article on how to wind my own oputput transformer? Thanks.

:Sure, it can't be that critical. Who knows what the speaker impedance is anyway? Try it and see.

Are you kidding? Don't you know that if parts that are off by even 1 millionth of one percent are substituted in sets designed with 20% parts that the world will tilt on its axis, thus destroying all civilization? Please Alan, be more careful with your advice.

Joe: The 71A tubes connected as pentodes should have a plate load impedance of 4800 ohms or 5K rounded off. You need a 10,000 ohm center tapped output transformer. My data shows the speaker to be 10 ohms, so an 8 ohm secondary would be close enough. They measured these old speaker Z's at 400 hz anyway.
Good Luck.: Ihave a Philco model 20 with an open primary in the output transformer. Does anyone know what impedance is needed for the 71A's in push pull configuration and if a universal output transformer will work?