06-25-2023, 08:06 PM
Hi Mike,
While I was writing this, RadioRoslyn put up a much better post than I did. I am leaving this but read his post also, as he has a VERY good article attached1
Personally, I am not a fan of the speaker that was originally installed in the model 20 (and likely the 70 and 90 as they are very tinny. I installed a modern speaker in my 20 and am much happier with the tone. Since mine is a Frankenradio to begin with, I was not quite worried abut authenticity.
In your post of approximately 7:20 PM, are you describing the "bad" transformer as being from the original speaker or from the one purchased from e-Bay? If you are describing the original speaker, there are 3 leads from the speaker. One lead is from the Output Trans primary to the plate of the 47. Another wire is shared with the B+ connection of the output transformer primary and the field coil. The 3rd wire is from the field coil to a voltage divider that supplies B+ to the screen grids of the 24As.
I have attached the diagrams for the 90 and 90A to this post for your convenience (these are from Nostalgia Air, there may be better ones in the Philco Library.
Trace these wires out. It seems that either the output transformer or the field is open. If the output transformer is open, then you have to find a replacement. Use the transformer that Morzh recommended. If the field is open and the transformer is good on the original speaker, and if the field is good on the new speaker, then install the original transformer on the new speaker.
Note the very low voice coil impedence on these speakers on the chart that RadioRoslyn supplied vs the 3, 4 0r 8 Ohm impedence of more modern speakers. this must be taken into consideration if a non-philco replacement transformer needs to be found.
While I was writing this, RadioRoslyn put up a much better post than I did. I am leaving this but read his post also, as he has a VERY good article attached1
Personally, I am not a fan of the speaker that was originally installed in the model 20 (and likely the 70 and 90 as they are very tinny. I installed a modern speaker in my 20 and am much happier with the tone. Since mine is a Frankenradio to begin with, I was not quite worried abut authenticity.
In your post of approximately 7:20 PM, are you describing the "bad" transformer as being from the original speaker or from the one purchased from e-Bay? If you are describing the original speaker, there are 3 leads from the speaker. One lead is from the Output Trans primary to the plate of the 47. Another wire is shared with the B+ connection of the output transformer primary and the field coil. The 3rd wire is from the field coil to a voltage divider that supplies B+ to the screen grids of the 24As.
I have attached the diagrams for the 90 and 90A to this post for your convenience (these are from Nostalgia Air, there may be better ones in the Philco Library.
Trace these wires out. It seems that either the output transformer or the field is open. If the output transformer is open, then you have to find a replacement. Use the transformer that Morzh recommended. If the field is open and the transformer is good on the original speaker, and if the field is good on the new speaker, then install the original transformer on the new speaker.
Note the very low voice coil impedence on these speakers on the chart that RadioRoslyn supplied vs the 3, 4 0r 8 Ohm impedence of more modern speakers. this must be taken into consideration if a non-philco replacement transformer needs to be found.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
