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49-500 2nd IF Transformer Question - Printable Version

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49-500 2nd IF Transformer Question - SRv2 - 04-30-2026

Hey guys,
I have a 49-500 that I am working on.  I have the recap done, tubes tested, resistors checked, new power cord, cabinet cleaned/repaired, etc, etc.
But, I have one resistor with some drift and I am unsure if I need to try to replace it.
Here is the schematic for reference.

Within the 2nd IF Transformer can is R300, a 47K ohm resistor.  When I measure resistance from the green to white wires of the can, I am getting 70.2K Ohm, instead of the expected 47,020 ohms across the secondary of Z300 and R300. Seems that R300 has likely drifted high.  

My concern is that a 70k load here is going to mess with the detector diode loading and the AVC, maybe leading to distorted audio or poor gain on stronger stations? Does that seem like a fair concern?

I’m usually reluctant to pull these cans and risk the internal fine-wire connections just to swap a resistor. For those who have restored this chassis:
  1. How critical is that 47k value to the final performance?
  2. Is it worth the "surgery" to replace it, or have you found that these sets tolerate that much drift in the detector stage?

Thanks for any feedback,
George
   

RE: 49-500 2nd IF Transformer Question - SRv2 - 04-30-2026

Well being the impatient person that I seem to be cursed with, I went for it.  Pic attached.  Replaced the drifted resistor, successfully reassembled.  Afterwards, primary reads 22 ohms, then across secondary + R300 reads 46.8K ohms.  Boom!
   

RE: 49-500 2nd IF Transformer Question - SRv2 - 04-30-2026

Ok well it is a very short video and unaligned and the loop needs connected better. But, it’s alive!!!
https://youtube.com/shorts/wSiUAnt5TSQ?si=96nEXfmGt-YLSjeo

RE: 49-500 2nd IF Transformer Question - RodB - 04-30-2026

Good job, George! Icon_thumbup That was fun, wasn't it?

RE: 49-500 2nd IF Transformer Question - SRv2 - 04-30-2026

Heck yeah! We went out to celebrate to A&W drive up for ice cream!!
   

RE: 49-500 2nd IF Transformer Question - radiorich - 04-30-2026

Hello George,
One of my favorite childhood places was tied to a local family my father grew up with in my hometown. They had about four of these spots in the area, and I remember one of the last ones had a root beer keg with a beer-style tap to fill your mugs.

Sincerely Richard

RE: 49-500 2nd IF Transformer Question - SRv2 - 04-30-2026

Hi Richard,
This one has that old keg and tap! It’s been here forever and still going. We heard once that there are only a few A&W drive ups left. I think my wife and I are keeping this one going.
George

RE: 49-500 2nd IF Transformer Question - Arran - 05-01-2026

George;
I've had to take those 1940s era Philco IF cans apart myself a few times, last time I think I had to do something with the trimmer screws in the top. From what I remember they are easier to get apart then back together, that flat spring is a real A-hole to get back through the two slots on either end. After several tries I think I ended up disconnecting the leads, and taking the can off, to get that spring back in, the center bump is what makes it difficult as that has to fit inside the tube for the coil, then the end has to somehow be pushed up until it catches in the other slot. I wish they had made them more like the RCA ones where they had a 1/4'' nut that held the coils assembly in that can, but Philco had to do their own thing here.
Regards
Arran