Philco 37-89 Ist IF - Printable Version

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+--- Thread: Philco 37-89 Ist IF (/showthread.php?tid=25007)

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Philco 37-89 Ist IF - dconant - 04-30-2024

Hello, Working on a Philco 37-89. I needed to take out the 1st IF because 2 wires were falling apart. The schematic (Riders 7-29) shows only 4 wires. The black wires in the picture are the ones with bad insulation. They are not on the schematic. One wire goes to pin 5 of the 6K7 (IF) tube and the other goes to ground. There is no other wire connected to pin 5 but the schematic shows pin 5 going to ground. I ohm out the black wires and I get about .3 ohm. It looks to me like the black wires are wrapped around the core abut 2 times. Any idea what this is for? It is going to be tricky getting new wires on there. Looks like I will just splice as far in as I can. There is nothing like that on the 2nd IF.

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RE: Philco 37-89 Ist IF - Radioroslyn - 04-30-2024

https://philcoradio.com/library/download/service%20info/service%20bulletins/Philco%20Service%20Bulletin%20278.pdf

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RE: Philco 37-89 Ist IF - dconant - 05-01-2024

Ah I might have known there would be a different schematic. My chassis does not have a label stating what model or run it is. All I had was the tube chart in the cabinet. Thank you.

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RE: Philco 37-89 Ist IF - Radioroslyn - 05-01-2024

Mostly the difference between the '37 an '38 model chassis is the conversion to octal from standard based tubes. I suspect that the loop is used to add a little bit feedback to the IF amp stage. This in turn boosts the gain. A lot of pentode IF amp tubes the suppressor grid and cathode are internally connected so this sort circuit couldn't be used. Phasing is important without it no feedback will happen

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