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 Post subject: Automatic P-60 cord replacement.
PostPosted: May Mon 10, 2021 12:06 am 
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Joined: Feb Fri 01, 2019 11:35 pm
Posts: 638
Location: Riverside Ca. 92504
I am starting to restore a automatic tube radio model P-60 made aprox. 1942. It has a cord that has a lot of kinks in it and I was going to replace it. The problem is I have never seen a cord installation like this and wonder if it can be replaced with a regular cord with two strands. I replaced the E caps and stopped till I can figure out how to replace it. It reads 120 across it The center part reads 120 volts across the black wire . Tom


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 Post subject: Re: Automatic P-60 cord replacement.
PostPosted: May Mon 10, 2021 1:56 am 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 3824
Location: Austin, Texas
It looks to me like the 547 ohm resistor in series with the 35Z5 filament is built into the power cord. That would not be unusual for a 1940 radio.
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To change to a regular power cord, you will need to make some minor changes to the radio.

Solution 1: Replace the 35Z5 with a 117Z6. That eliminates the need for the resistor but the rectifier socket needs a jumper wire between pins 3 and 5 and another jumper wire between pins 4 and 8. Those pins may not be in the socket or they may be used for other purposes.

Solution 2: Replace the 547 ohm part of the power cord with a 3.5uF, 250VAC, rated capacitor such as used on fan motors. No changes are needed to the 35Z5 wiring.
https://www.amazon.com/CEILING-CAPACITO ... B017G62TF4

You could also use a resistor to replace the 547 ohm part of the cord but the power dissipation would be over 12 watts so it would be a heat problem.

If you need more details, let us know.

Jay


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 Post subject: Re: Automatic P-60 cord replacement.
PostPosted: May Mon 10, 2021 2:20 am 
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Joined: Feb Fri 01, 2019 11:35 pm
Posts: 638
Location: Riverside Ca. 92504
Thanks Jay.. So from the black wire that does not go to the switch ( red does ) jumper the black wire to the filament with the cap. and change the cord.?? That seems like the easer solution. Planer just take the cord off and attach the cap from the black wire to where the resister wire comes in. Does that mean that the cord has to go in the receptacle a certain way to work ?? Why did they use resister cord ?? Seems easier to build the resister into the chassis. Tom


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 Post subject: Re: Automatic P-60 cord replacement.
PostPosted: May Mon 10, 2021 2:43 am 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 3824
Location: Austin, Texas
tomb123 wrote:
Thanks Jay.. So from the black wire that does not go to the switch ( red does ) jumper the black wire to the filament with the cap. and change the cord.?? That seems like the easer solution. Planer just take the cord off and attach the cap from the black wire to where the resister wire comes in. Does that mean that the cord has to go in the receptacle a certain way to work ?? Why did they use resister cord ?? Seems easier to build the resister into the chassis. Tom

Tom,
To use the cap, you would connect the wires of the regular cord where the red and black wires are now. Since the red wire goes to the switch, the cap connects from the black wire to the place where the original white wire went.

If you use a cord with a polarized plug, I would connect the neutral wire (wide blade) to the power switch. That may sound wrong but the wire to the switch connects to the B- rail when the radio is on. That will usually result in a little less noise than connecting the hot wire to B-.

The resistor cord was used to eliminate a hot resistor inside the radio cabinet. It may also have been cheaper than the resistor and the mounting needed to keep it away from other parts.

No heat problem with the cap. You can put it anywhere you can find the space. They might have used a cap in the original design if they had the high value film caps we have today.
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Jay


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 Post subject: Re: Automatic P-60 cord replacement.
PostPosted: May Mon 10, 2021 4:48 am 
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Joined: Feb Fri 01, 2019 11:35 pm
Posts: 638
Location: Riverside Ca. 92504
Thank you .. At my age the pic is great so I will not screw it up. I had thought that it was wired that way but I forgot about the polarity on the plug. From the schematic I thought the chassis was ground and I was a little worried on working on the hot case. I will have to break out the vari trans. to keep working on it. I E capped it and wanted to test it to see if I got some noise out of it. It is going to get a complete cap change and probably most of the resisters.. I Am waiting on my order of caps to come in. The older schematics with out a part list are a little harder for me to figure out. That charging section is also different. Thanks Again. Tom


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