[Sourbone]

I am replacing an output transformer on a model 650. I have a Hammond 125E output transformer. I'm trying to determine which lugs to connect to the speaker from the secondary. Please educate me. I'm halfway there. I was looking at Franks Electron tube data sheets page. The RCA literature for the 42 tube in push pull configuration says the load impedance is 10,000 ohms. Is this the info used for determining the correct output transformer secondary lugs? The speaker voice coil is about 1 ohm. So I would think that the secondary lugs 4 & 5 on the Hammond 125E would be correct. Is my thinking correct? Thanks for your help. Dave

[Ron Ramirez]

The original transformer matched 5,900 ohm load impedance to a 1.25 ohm voice coil impedance.

Using the chart above, secondary lugs 1 and 3 will give the closest match.

[Radioroslyn]

Typically triodes have a lower plate impedance than pentodes. Even pentodes that are wired as a triode. When trying find the proper impedance most tube manuals don't list penodes in that configuration. Good thing Ron has the info for the original.

Terry

[Sourbone]

Thank you. Glad I'm checking with the experts. So on the RCA tube data sheet, the option with the screen grid connected to plate in push pull configuration would be the correct load impedance? 6000 ohms? fixed bias. 

Thanks again, 

Dave

[Ron Ramirez]

Dave (Sourbone)

Did you see my post #2 above?

The info was taken from original Philco documentation.

[Sourbone]

Ron, I have the schematic and parts list. I didn't see the info there. If I encounter this replacement on another radio, what source should I refer to. Thanks for your help always. 

Dave

[Sourbone]

Hey Ron, Thanks for keeping the phorum running. It's terrific.