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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Sun 03, 2019 8:54 pm 
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RadioRanger wrote:
Okay thanks for the info on the different sized .05MFD @ 400V capacitors.

Just a follow up on item 2 regarding the capacitor that is coming off the volume control, that is in fact C9 on the schematic? I was not sure just trying to get confirmation.

Any idea on which type of capacitor I should by, Film, Poly, Mica? I've been looking for the 5MFD 25V not able to get the exact rating. Can i use a 4.7mfd at 25V. Also looked for a 5mfd at higher voltages but not able to find.

Thanks

Norm had recommended 630 volt capacitors, and when dealing with tube radios, that's what you want to stick with. The 25 volt varieties, while acceptable in one specific application in some sets, are mainly for Transistor circuits.

You can use film or poly; the circuit won't care, as long as it's a capacitor. No reason to use mica except generally in the front end osc circuit. 5 uF is an antiquated value. Use 4.7 uF as the closest substitute.

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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Sun 03, 2019 9:29 pm 
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I want to second the suggestion that the capacitor circled in the last photo appears to connect to the switch, not the volume control.

It might help to know where each end of the capacitor goes. Particularly, since the schematic shows no capacitor connected to the switch.

Ted


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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Mon 04, 2019 2:17 am 
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The volume control is also the on off switch, the other side of the capacitor runs through to the second I.F. via a dog bone (I think its a resistor).


Thank you!


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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Sat 16, 2019 11:02 pm 
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Well, I'm reaching out once again. After replacing all of the capacitors in the radio the audio continues to fade after a few minutes. No improvement. Any next steps would be greatly appreciated.


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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Sun 17, 2019 12:09 am 
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You had a capacitor on the on-off switch with no markings. Can you peel off some more of the paper covering to see if it is a coil, not a capacitor? If so, it may be item 1 on the schematic, vibrator RF choke.

What are you using for 6 volt supply?

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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Mon 18, 2019 2:05 am 
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While doing the capacitor replacement, I did notice it was a coil so I did not replace it. Looking at the end of the paper tube I could see two winding of wire at one end of the tube. Okay this is the choke, I will note that.

I have a power supply that was build by a fella that had done so on a restore he did on the very same radio. it reads 6 volts on its output.

The strange thing, is the radio sounds perfect when it starts up, and slowly loose volume, after a few minutes the volume finally cuts off.

stumped.


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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Mon 18, 2019 6:06 am 
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Connect your meter leads to the power supply, and monitor it's output while the set is on, to determine if it's the source that's dying.

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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Fri 22, 2019 8:56 pm 
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Results from the power supply test.

With the power supply connected to radio drawing power, after approximately 2-3 minutes the power supply plunges from 6 volts down to under 5 volts at that point the radio cuts off.

Under no load the power supply continues to produce 6 volts without fail.


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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Fri 22, 2019 9:19 pm 
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It sounds like once the circuit gets hot, something is shorting out, causing the voltage to drop and the current to increase. As soon as that occurs again, unplug it, and quickly check the values of the resistors and capacitors.

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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Sat 23, 2019 12:10 am 
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Also, what is the amperage spec on the power supply? I have the same radio and it takes about 2 to 2.5 amps at 6v to run it.

Does the vibrator continue to run?

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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Sat 23, 2019 4:27 am 
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jrehkopf wrote:
Also, what is the amperage spec on the power supply? I have the same radio and it takes about 2 to 2.5 amps at 6v to run it.

Does the vibrator continue to run?

Good point. Both of my Zenith 6 volt farm sets with vibrators need 2+ amps to operate.

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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Mon 25, 2019 5:12 pm 
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6 volts with 1.6 amps from the power supply was marked at the start of the test. Vibrator and audio operate.

At 5.3 volts with 1.2 amps the audio cuts out. Voltage stabilizes at 3.07 volts with .97 amps; vibrator continues to operate.


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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Mon 25, 2019 6:10 pm 
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If you all think this is a power supply issue, would a power supply like this one in the link below work? Looks like the voltage is adjustable at 2.5 amps. Not sure about the wattage (65W)? With some reconfiguration I think I could tuck this away in the cabinet.

https://www.amazon.com/3V-Adjustable-Adapter-Control-Variable/dp/B07QVXYBDC/ref=sr_1_7?keywords=6V+dc+2.5A+power+supply&qid=1574700744&sr=8-7

Thanks


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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Mon 25, 2019 9:09 pm 
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Before spending your money on another one, try that power supply on something else for an hour or two. If it again punks out, then it should be trashed. If not, there's more than likely a problem in the radio's circuit.

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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Tue 26, 2019 12:10 am 
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That eBay supply is probably noisy, a switching supply. How about try your local hardware store or farm supply and get a 6 volt battery used for electric fencing? Maybe 10 bucks and should run the radio fine for an hour or two.
Edit: does not work. I tried it.

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Last edited by jrehkopf on Nov Wed 27, 2019 11:51 pm, edited 1 time in total.

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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Tue 26, 2019 1:47 am 
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What can you tell us about your existing power supply? Make? Model? Ratings? Photos?

Agree that a switching supply is likely to be nothing but RF noise powering a radio.

Ted


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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Wed 27, 2019 3:43 am 
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All,

Attached are some pictures of the power supply that was built for this radio. I've taken close shots of each component, and an overall shot so you can see how its wired. there is noting on the underside of the board, just the bottom of the pot switch and some connecting wires to the components above.

Note: the pot switch is used to adjust the voltage, presently set at 6volts.

Appreciate your continued support on this project.


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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Wed 27, 2019 3:51 am 
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Again, I would suggest trying it on another radio or device that takes 6-12 volts at two amps for an hour or so, to see how it holds up. That would be the best way to either ID or eliminate it as the cause of the problem.

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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Wed 27, 2019 4:07 am 
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Okay... I need to search for some type of device to test as I don't have one on hand.

From what you've seen from the photographs are any of the components under powered for this application?

Thanks


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 Post subject: Re: Zenith 4V31Farm Radio - Restoration
PostPosted: Nov Wed 27, 2019 4:33 am 
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All would a 6 volt light or fan work to test the power supply, I think I can source either quickly.


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