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 Post subject: Questions About GE F-63 Components
PostPosted: Jan Sat 07, 2017 5:30 pm 
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Location: Fort Worth, TX 76108
I'm working on a GE F-63 radio. The schematic is at http://www.nostalgiaair.org/pagesbymodel/794/M0007794.pdf. Unfortunately, a lot of the numbers on the schematic aren't readable. Also, being relatively new at this hobby, there are some components that I'm not sure of and a resistor wattage that I wonder about. See photos. Two photos have a ? for the component indicated. I'm guessing they are resistors but I'm not sure. Also, resistors R10 and R11 are in series per the schematic and I can't read the voltages. Since R10 is much larger than R11 (see photo), I suspect it's wattage rating should be higher than 1/2. R10 is supposed to be 15K ohms but it measures at 17K ohms and should be replaced. Any idea on what wattage the replacement should be?

This radio is pretty challenging for me. In addition to replacing electrolytics and paper/wax caps, most of the resistors measure out of tolerance high and will need replaced. There's also a lot of wiring with crumbling insulation that will require replacement.

Thanks,
Larry

Edit: Found a youtube video about dog bone resistors in a 1930's GE radio which answers my questions about what the components are. The yellow body dog bone looks to be a 4.7K resistor and the brown body dog bone looks to be a 10k resistor. The brown body resistor should be R9 in the schematic. Since R9 is also large, I'm still curious about what wattage it and R10 should be.


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Unk2.jpg
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 Post subject: Re: Questions About GE F-63 Components
PostPosted: Jan Sat 07, 2017 6:41 pm 
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Your first picture shows a 10K resistor. At first I thought it was 100K (judging the dot to be yellow), but the only 100K resistor is R15, and that one would have no reason to be a higher wattage resistor like this one is. Taking a close look at the picture again, it appears the dot could be orange, which would make this R9, which should indeed be a higher wattage resistor.

You've got three resistors in series forming a DC voltage divider. The schematic gives the voltages at all points in the divider, so we can use the following formula to calculate the actual power dissipated in each resistor:

P = V^2 / R

Since R9 has 250 V on one end, and 98 V on the other end, the voltage across R9 is 152 volts, and the formula above gives the power dissipated by R9 to be 2.3 watts. The original resistor is probably somewhere in the range of 3-5 watts rating. I'd replace it with a 10K 5 watt resistor. This is a bit of overkill in terms of dissipation, but resistors with 3 or 4 watt ratings are not so commonly available these days.

The next resistor in this same voltage divider is R10, which is 15K, and has voltages of 98 V and 1.2 V on each, for roughly 97 V across the resistor. Dissipation in this resistor is 0.63 watt. A 1 watt resistor is sufficient here, or you can use 2 watts if you want to provide extra margin.

The final resistor is R9, which is 180 ohms, with only 1.2 V across it. Dissipation is 0.008 watt, so you can see that the original 0.5 watt resistor is plenty big enough.

Your second picture shows a 4.7 K resistor, but I don't see a 4.7 K value on the schematic, so it's not clear what this is. Can you describe what is connected to both ends of it? The colors in the picture appear unambiguous, so I don't see how it could be a value other than 4.7K.

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 Post subject: Re: Questions About GE F-63 Components
PostPosted: Jan Sat 07, 2017 7:43 pm 
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Location: Fort Worth, TX 76108
Tom, thanks for the voltage and watts info. You must have a schematic that is more readable than mine. Is there a link to it that I could use?

The 4.7k resistor connects to terminals 2 and 3 from the left on the terminal strip. I've attached another photo. Other connections to terminal 2 are one end of R12*, a wire that goes to pin 5 and on to pin 6 of the 41 tube, and a wire that goes to a terminal on C3 (broadcast padder). Other connections to terminal 3 are one end of R6* and a wire that looks like it goes to a terminal on the band switch (S1).

* I'm about 95% sure that I've identified R12 and R6 correctly.

Larry


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 Post subject: Re: Questions About GE F-63 Components
PostPosted: Jan Sat 07, 2017 8:14 pm 
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Still not clear what that 4.7K resistor is. It looks like terminal 2 on that terminal strip is actually grounded to chassis via the mounting rivet. The other terminal does appear to have a 22K resistor on it, which could be R6, provided that black wire goes to the tone control switch, not the bandswitch. If this interpretation is correct, then this resistor is not on the schematic. Might be interesting to try the radio both with and without this resistor. It appears it might be adjusting the response of the tone control.

I'm simply looking at the Rider schematic on Nostalgia Air. I agree it's not too easy to read, but I think I can read it. I have the original book out in the shop, but did not go and check it.

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 Post subject: Re: Questions About GE F-63 Components
PostPosted: Jan Sat 07, 2017 8:32 pm 
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There's a nice sharp schematic and parts list in Volume 7 pages 1210 and 1211 of the Gernsback Manual, available for free download from http://ebaman.com/index.php/remository/ ... onic-docs/
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 Post subject: Re: Questions About GE F-63 Components
PostPosted: Jan Sat 07, 2017 9:22 pm 
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Location: Fort Worth, TX 76108
Tom, the black wire from 1st terminal on the strip goes to the tone switch and what I think is R6 is between the first terminal and the 3rd terminal on the strip. The black wire coming off the third terminal bends under mica capacitor C4 and then towards band switch. And you're correct, second terminal is grounded to the chassis. It will be awhile before I can power the radio. Lots of replacements to do yet. Thanks for your help!

Glenster, thanks for the link to the Gernsback manuals!

Larry


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 Post subject: Re: Questions About GE F-63 Components
PostPosted: Jan Thu 12, 2017 9:55 pm 
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Joined: Aug Sat 08, 2015 9:50 pm
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Location: Fort Worth, TX 76108
Tom Albrecht wrote:
Still not clear what that 4.7K resistor is. It looks like terminal 2 on that terminal strip is actually grounded to chassis via the mounting rivet. The other terminal does appear to have a 22K resistor on it, which could be R6, provided that black wire goes to the tone control switch, not the bandswitch. If this interpretation is correct, then this resistor is not on the schematic. Might be interesting to try the radio both with and without this resistor. It appears it might be adjusting the response of the tone control.

Tom, you were correct about the black wire going to the tone control switch. Since it had deteriorated insulation, I replaced it and found that it went under the band switch and on to the tone control. I powered up the radio and it plays well. There are 3 positions for tone control. The first position seems to be minimal bass and the next two positions seem to have the same amount of increased bass. I took the 4.7K resistor out of the circuit and then had a high pitched whine in the sound. I put in a new 4.7k resistor and the whine is gone. Again, thanks for your help!

Larry


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