[kenlew0405]

Hi everyone,
I recently got a partly refurbished Philco 77, but the volume rheostat/ potentiometer doesn’t work (it sparks and smokes). Can anyone tell me what kind of rheostat/ potentiometer I need to replace it (a Mouser number would be great)? I don’t quite understand what the schematic is indicating.

Thanks a bunch
Ken


Schematics can be found here: http://www.nostalgiaair.org/PagesByModel...013838.pdf

[murf]

Hi everyone,
I recently got a partly refurbished Philco 77, but the volume rheostat/ potentiometer doesn’t work (it sparks and smokes). Can anyone tell me what kind of rheostat/ potentiometer I need to replace it (a Mouser number would be great)? I don’t quite understand what the schematic is indicating.

Thanks a bunch
Ken


Schematics can be found here: http://www.nostalgiaair.org/PagesByModel...013838.pdf

I would contact Mark Oppat on that one.
I am sure he would have the switch for you.
murf

[kenlew0405]

Thanks murf. I'll contact him and see if he can help.

Hi everyone,
I recently got a partly refurbished Philco 77, but the volume rheostat/ potentiometer doesn’t work (it sparks and smokes). Can anyone tell me what kind of rheostat/ potentiometer I need to replace it (a Mouser number would be great)? I don’t quite understand what the schematic is indicating.

Thanks a bunch
Ken


Schematics can be found here: http://www.nostalgiaair.org/PagesByModel...013838.pdf

I would contact Mark Oppat on that one.
I am sure he would have the switch for you.
murf

[Radioroslyn]

That one to is going to be really hard to find as a new part. It's a dual pot one half controls the RF gain and the other half control amount of rf that is coupled from the antenna to the 1st RF amp.
Best bet is to try to fix the one you have or get one from a model 20,70,or an early 90 parts set.
GL
Terry

[Radioroslyn]

There's a 77 chassis up for auction at you know where. Might make a good donor.
Terry

[kenlew0405]

Hi everybody,

Well, I feel like a real jerk! After all this research, getting the converter kit from Mark Oppat, and all the great help from the forum, I realized I was looking at the schematic for the wrong model! I am working on a Philco 65, not 77 (they look similar from the outside). So i guess my next question is, can I use the 10000 ohm pot that came with the converter kit to replace the (simple) 5000 ohm pot that the 65 has?

Thanks for all your help!

[morzh]

Kenlew

Where on the 65 sch do you see 5K pot? I looked at the sch here in the Resources, and then on Nostalgiaair, and there is none.
if you look in their Rider manual, in the beginning there is the Mod. 87 that does have 10K pot, and then the 65 that does not.
And, the 77 does have 5K pot (dual, 5k/250 ohms) according to the sch.

Can you first straighten this all out?

[Ron Ramirez]

http://www.philcoradio.com/tech/images/65.jpg

The volume control is part (25) on the Model 65 schematic; a 1,750 ohm rheostat. It controls the screen grid voltages of the two 24 RF amplifier tubes.

[morzh]

Ron,

Yes, that one I saw, but it is in no way close to a dual pot, especially given the values of 5K/250 ohms or a 10K one.

I am not sure what Kenlew meant by 5K pot, and how he wants to fit a 10K i/o 1.7K one.

Now that he told he was looking at the 65 schematic, and not the 77, I have doubts that he really did.

[kenlew0405]

Ron,

Yes, that one I saw, but it is in no way close to a dual pot, especially given the values of 5K/250 ohms or a 10K one.

I am not sure what Kenlew meant by 5K pot, and how he wants to fit a 10K i/o 1.7K one.

Now that he told he was looking at the 65 schematic, and not the 77, I have doubts that he really did.

Yes, I was wrong again. The pot is 1750, so I think the 10k is too much.

[morzh]

Man, you've got to stop working late

[morzh]

Other manual shows 2K, but that beside the point.

This pot needs to dissipate quite a bit, huh.....3W dissipation will make it 5 to 7 W rated pot at least.

I was about to suggest trying to trick that thing: you can connect a large, say, 6-8W resistor of 2.1K in parallel to the ends of the pot (the circuit will see an equivalent of 1.72K) and try to regulate it this way, but I am not sure what the 10K pot's rated dissipation is - needs to dissipate 1/2 Watt, so needs to be 1-2W rated at least.

You can try.....

[Radioroslyn]

Another solution to your problem would be to change the manual gain control (the dual pot) to AVC (automatic volume control) This you would only need a single pot of 250K to a meg ohm along with a few resistors, couple of caps, and a diode like a 1N34.
Terry

[kenlew0405]

The wattage of the pot was my next question, so it should be at least 5w. Does it hurt to go bigger if I can find one @1750 ohms?

Other manual shows 2K, but that beside the point.

This pot needs to dissipate quite a bit, huh.....3W dissipation will make it 5 to 7 W rated pot at least.

I was about to suggest trying to trick that thing: you can connect a large, say, 6-8W resistor of 2.1K in parallel to the ends of the pot (the circuit will see an equivalent of 1.72K) and try to regulate it this way, but I am not sure what the 10K pot's rated dissipation is - needs to dissipate 1/2 Watt, so needs to be 1-2W rated at least.

You can try.....

[kenlew0405]

You know it. Waiter, more coffee!

Man, you've got to stop working late