Philco 77

[Zsuttle]

Originally Posted by old_coot88

Here's the schematic..

http://www.nostalgiaair.org/Resource...=\M0013838.pdf

That's the one I've been using as well as this one, which is nearly identical and has most of the values. http://www.philcoradio.com/images/phorum/schem/76.jpg

No output transformer that I can see, the 45's plates go directly to the speaker. Not sure if it ever worked, either way, can someone help me figure out the maximum wattage I'll need? The datasheet calls for like 18 watts max watts in a push pull configuration.

http://www.hammondmfg.com/125H&J.htm
The Hammond 125 series seems to suit the resistance needs fairly well

This is the datasheet that I've been using
https://frank.pocnet.net/sheets/021/4/45.pdf

[old_coot88]

Originally Posted by Zsuttle

No output transformer that I can see, the 45's plates go directly to the speaker.

Your schematic definitely shows the output xfmr, designated #24. The field coil is #26, and the power supply choke #35. Can you post pics of the top and underside of the chassis? The output xfmr has gotta be there somewhere unless it's been physically removed.

(This design uses a dedicated field coil, whereas later designs made the field coil double as the choke).

(Edit.) In your photo of the speaker, it looks like the speaker has been replaced with the later type that uses the field coil as choke. Notice the two black wires coming out of the field frame. Those go to a 'hum bucking' coil which is in series with the voice coil. It serves to null out the field's ripple. Your radio doesn't need hum bucking, since the field coil does not double as choke. So just take the HB coil out of circuit, and run the voice coil direct.

[Zsuttle]

Heres pictures of my chassis.
20181012_151551.jpg
20181012_151628.jpg
The plates of the 45's go directly to the speaker plug. My understanding was that the output transformer was mounted on the speaker frame however, when they replaced the speaker, they bypassed any sort of output transformer and hooked it directly to the speaker. If you look at the schematic for the 77, you can see the plugs off of the 45 tubes and off of the field coil

[old_coot88]

Originally Posted by Zsuttle

Heres pictures of my chassis.

The plates of the 45's go directly to the speaker plug. My understanding was that the output transformer was mounted on the speaker frame however, when they replaced the speaker, they bypassed any sort of output transformer and hooked it directly to the speaker. If you look at the schematic for the 77, you can see the plugs off of the 45 tubes and off of the field coil

Yep you're right. Originally the p-p output xfmr was mounted on the speaker.

[Zsuttle]

My only other question is how do I determine the wattage I'll need?

This line seems to suit the demands given
http://www.hammondmfg.com/125a.htm

[EdKozk2]

A 10 watt p-p should be just fine for your Philco.
Ed

[Zsuttle]

Well, I'm happy to report that I received the transformer today and promptly installed it. I'm also happy to report that I'm now receiving stations, though slightly garbled and with a high pitched whine. I'm assuming that aligning each section should fix the whine, though I'm not sure about the garble. (Weak output tubes maybe?)
Thanks for everyone's help,
Zach