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 Post subject: Silvertone 6297 Car radio newbe help
PostPosted: Jan Sat 05, 2019 6:11 pm 
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Hi all! I am new to antique radios and this forum and need some help. I purchased an antique (not sure what year) Silvertone 6 volt car radio model 6297-1 to install in my 1937 Ford Truck. I replaced all the capacitors prior to powering on. When powered on all the tubes light up but I don’t have any high voltage at the rectifier tube (6X5GT). The Vibrator does work and looking at the voltage wave form on an oscilloscope it appears to be a square wave of about 6 volts at the two output pins. However, there is no voltage at the output of the transformer secondary just noise (on the scope). I measured the resistance of the transformer primary (~.2 ohms) and the secondary (1100 ohms). I don’t have any info on what the values should be but they seem reasonable so I am at a loss as to why I am getting no output. I also tested the voltages with the 6X5GT removed and got the same results. My guess is the transformer is bad but would like opinions on that. If it is bad how do I determine what replacement to use since I don’t know what the primary and secondary resistances should be. Any help would be greatly appreciated.
Thanks,
Charlie


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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Sat 05, 2019 6:53 pm 
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Location: Mountains of Mourne. Ireland.
http://www.nostalgiaair.org/Resources/479/M0017479.htm

Greg.


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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Sun 06, 2019 5:17 am 
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Check that cap c-21, that is across the secondary of the transformer. It needs to have a very high voltage rating to survive spikes from the vibrator and the step-up transformer.

If you shop around, you can probably find another 6 volt car radio for parts. Look for radios that have a 6V6 output tube, and the transformer will be similar. Just a suggestion.


This website has some interesting pictures of similar Silvertones. The Model 6284 matches the drawing on the schematic pages.

https://sites.google.com/site/identifyi ... rs-roebuck

You could send them a picture of yours with the model number.

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Burl Ives, RIP, oldtimer.
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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Mon 07, 2019 10:00 pm 
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Location: Shelton, WA
You can try to measure from the center taps of the primary and secondary. The primary is 20 ohms to each leg and if the secondary from center tap to each leg is about the same then most likely the transformer is ok.

You will want to make sure the center taps are connected to ground.

You can also look at the ac voltage at the secondary of the transformer. 235 (?) ac

billn


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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Wed 09, 2019 10:34 pm 
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Joined: Jan Sat 05, 2019 5:39 pm
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Location: New Jersey
Thank you for the replies. Here's the latest.
I also have an RCA 6v radio that reads 6.5v at the primary and 240v at the secondary. I measured the transformer to compare to the Silvertone. The RCA primary measures 2-3 ohms from ground to each side of the transformer and 308 and 348 ohms on each side the secondary to ground (center taps grounded). Across the primary it measures 2-3 ohms and across the secondary it measures 654 ohms (end to end).

The silvertone primary measures 2-3 ohms from ground (center taps grounded) to each side of the transformer and 534 and 576 ohms on the secondary to ground. Across the primary it measures 2-3 ohms and across the secondary it measures 1108 ohms (end to end). The primary waveform looks good but there is no output voltage. It seems there should be something on the output because the values are not that far off. I could try to connect the RCA vibrator transformer to the Silvertone to see if it works. Any thoughts.


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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Wed 09, 2019 11:09 pm 
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Perhaps I misread your description, but only the secondary center tap of the transformer goes directly to ground according to the schematic link provided by Egg. The center tap of the primary does not go directly to ground, but it is connected to the heater of the 6X5GT rectifier, the other side of which does go to ground. Might that be an issue?

-Bryan


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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Thu 10, 2019 2:54 am 
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Location: Shelton, WA
Hi Bryan,

No the center taps are correct. You might want to sub the RCA xfmr for the Silvertone one and see what happens.

billn


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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Thu 10, 2019 4:59 am 
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If both centertaps go directly to ground, there is no voltage for the filament of the 6X5GT rectifier.

-Bryan


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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Thu 10, 2019 6:41 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Shelton, WA
That's correct. The primary center tap goes to the 6X5 filament and the secondary is grounded. You just might have a bad transformer.

billn


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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Thu 10, 2019 9:44 pm 
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Joined: Jan Sat 05, 2019 5:39 pm
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Location: New Jersey
Thanks again guys for your help.
My bad on the transformer center tap connections. You are correct only the secondary center tap is grounded.

All of the following was done with the rectifier tubes removed.
I connected the Silvertone vibrator to the RCA transformer and still no output. I then connected the RCA vibrator to the Silvertone transformer with jumper leads and the output voltages are good so it leads me to believe the transformer in the Silvertone is OK and the vibrator is bad.

I did the vibrator rejuvenation process (120v) on the Silvertone using a 40w light bulb and vibrator seemed to work fine. I was going to switch the RCA vibrator into the Silvertone but the internal connections are different. The Silvertone uses all 4 pins while the RCA only uses three. The Silvertone vibrator is Silvertone P/N A34-105 and the RCA is a Motorola 3333. Any info on these parts?

Is it possible that even though the rejuvenation appeared to work, when connected to 6v it does not. It does vibrate but there is only about a .2 volt square wave on the primary side. (Note; my initial measurements must have been wrong as far as the vibrator output of 6 volts on my first post.)


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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Thu 10, 2019 10:01 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Shelton, WA
Possible the Silvertone vibrator is the wrong one in the radio if you connected the RCA one and it worked.

billn


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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Fri 11, 2019 2:19 pm 
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Joined: Jan Sat 05, 2019 5:39 pm
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Location: New Jersey
Thanks for the reply Bill,
Just to clarify, I didn't put the RCA into the Silvertone because the schematics showed that they were wired differently. What I did was disconnect the wiring to the transformers in both so that the transformers were disconnected in each. Then I jumpered the output of the RCA vibrator (and the primary center tap connection) to the primary connections of the Silvertone transformer(3 wires). I powered the RCA so that the vibrator would work and looked at the secondary of the Silvertone transformer. At that point I had the 6 volt square wave at the primary of the Silvertone transformer and about 240 volts at the secondary. That is why I now think the Silvertone vibrator is bad even though it does vibrate. When I ran the 40watt light bulb test the bulb did dim alternately (60 cycles?) so is it possible for the vibrator to work during that test and not with 6volts applied?


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 Post subject: Re: Silvertone 6297 Car radio newbe help
PostPosted: Jan Sat 12, 2019 7:07 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1744
Location: Shelton, WA
I think you should try a solid state vibrator. Have done may dim bulb vibrator repurposing and some of them just do not work out.

Only way to know is with a good working vibrator.

billn


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