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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Sun 05, 2021 5:51 pm 
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After attaching the AM loop antenna I still picked up no stations, even after moving around the various tuning capacitors there was still nothing.

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Sun 05, 2021 10:57 pm 
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Eevee1 wrote:
After attaching the AM loop antenna I still picked up no stations, even after moving around the various tuning capacitors there was still nothing.
OK, so now it is time to do some trouble shooting.

First you are going to need another radio that is working. You will place it near the Philco and turn it on and tune it to approximately 1455 KHz on the AM Broadcast band (precision tuning is not required).

Then with the Philco radio turned ON, tune it to around 1000 KHz which is around 60% of the way to the right on the dial (the tuning capacitors will be around 60% open).

As you are tuning the Philco back and forth do you hear a signal swishing back and forth on the other working radio? It will sound like a station with no audio.

What you are trying to detect is the Local Oscillator from the Philco which should be broadcasting at a frequency 455 KHz above the spot on the dial that it is tuned to (1000 KHz, + 455 KHz = 1455 KHz).

Also, tell me what you actually hear coming out of the speaker on the Philco (hiss, static, hum, any noise whatsoever, anything you hear).

Curtis Eickerman

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Mon 06, 2021 2:40 am 
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I did the test, however the Philco made no form of response (HMMMMMM), on another radio I noticed a slight amplification of a staion, (Static + Station -> Station amplification, still Static) whenever the capacitor got to a certain point. I have another radio that has exceptional reception, when I set the other radio near it and did the same thing nothing happened. (Possible variable: there are 7 separate stations fighting for dominance in that one spot, I can tune into all of them. I cannot do this on the radio with poor reception.) On the first radio (Poor reception) there is one weak station that tuning to that certain point amplifies. Like I said, the Philco did literally nothing but hum. the other radios just had normal static. (With random stations mixed in.)

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Mon 06, 2021 2:43 am 
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Eickerman wrote:
Eevee1 wrote:
After attaching the AM loop antenna I still picked up no stations, even after moving around the various tuning capacitors there was still nothing.
OK, so now it is time to do some trouble shooting.

First you are going to need another radio that is working. You will place it near the Philco and turn it on and tune it to approximately 1455 KHz on the AM Broadcast band (precision tuning is not required).

Then with the Philco radio turned ON, tune it to around 1000 KHz which is around 60% of the way to the right on the dial (the tuning capacitors will be around 60% open).

As you are tuning the Philco back and forth do you hear a signal swishing back and forth on the other working radio? It will sound like a station with no audio.

What you are trying to detect is the Local Oscillator from the Philco which should be broadcasting at a frequency 455 KHz above the spot on the dial that it is tuned to (1000 KHz, + 455 KHz = 1455 KHz).

Also, tell me what you actually hear coming out of the speaker on the Philco (hiss, static, hum, any noise whatsoever, anything you hear).

Curtis Eickerman

I read it and misinterpreted it, I thought was listening for the noise while moving the capacitor, but I definantly heard a swishing sound on the weak reception radio.

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Mon 06, 2021 3:42 am 
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By chance I was removing a small blob of solder from the tuning coil wafers and I noticed that even powered off, touching the tuning coils with the metal tweezers generates static from the other radio. I moved the tuning capacitor around while the radio was off and noticed the same things happening on the other radio despite the power status of the Philco. I also noticed once on the Philco for some reason the speaker suddenly got very loud. The speaker normally is quite quiet so this surprised me. I turned the radio off and on again and the speaker was back to normal. I have two hypotheses on what happened. One: my solder spool had some line going across a few parts of the radio the chassis ground through a terminal strip and by extension the speaker negative, the speaker positive and whatever was connected to a terminal on the same strip, the ground of a tube and the bare chassis. I doubt this is the case because if it were to short circuit, shouldn't the speaker get quieter? And, after removing the line of solder, it was still loud. Hypothesis 2: I had unscrewed the lightbulb for some reason and maybe this gave it more power. The weird thing is I was not able to redo the sudden boost in audio the same way again. While it was loud I put the lightbulb back in and took it out and the speaker did nothing. I tried to replicate this a couple of times using this method, however to no avail.

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Mon 06, 2021 3:43 am 
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Also, I don't think I hear what you are describing.

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Mon 06, 2021 6:03 am 
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Eevee1 wrote:
Also, I don't think I hear what you are describing.
Here is an example... https://www.youtube.com/watch?v=JThxZk697Kw The first half of the video.

What may not be obvious is that it is just like receiving a radio station on the good radio.

If you are not hearing a signal in the good radio the local oscillator in the Philco does not appear to be working and we will next try to find out why.

Curtis Eickerman

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Mon 06, 2021 3:53 pm 
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Eickerman wrote:
Eevee1 wrote:
Also, I don't think I hear what you are describing.
Here is an example... https://www.youtube.com/watch?v=JThxZk697Kw The first half of the video.

What may not be obvious is that it is just like receiving a radio station on the good radio.

If you are not hearing a signal in the good radio the local oscillator in the Philco does not appear to be working and we will next try to find out why.

Curtis Eickerman

I think I may have heard what is in that video, I will redo the test before troubleshooting, also what do you mean good radio? Both radios need some adjustments, but for the most part are good radios.

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Mon 06, 2021 7:42 pm 
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Eevee1 wrote:
I think I may have heard what is in that video, I will redo the test before troubleshooting, also what do you mean good radio? Both radios need some adjustments, but for the most part are good radios.

Nevermind the oscillator is defiantly broken.

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Mon 06, 2021 9:32 pm 
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Eevee1 wrote:
Nevermind the oscillator is defiantly broken.
You say this because you definitely are not hearing anything, or because you see something that definitely is "broken"?

Here is the schematic of the portion of the radio that involves the local oscillator.
Attachment:
48-1256 Front End.png
48-1256 Front End.png [ 65.57 KiB | Viewed 307 times ]
It would be good to check the voltages on the 7A8 which is the Oscillator/Converter tube. Also, though it is not shown, if you are using a high impedance voltmeter the DC voltage at point E should be a couple of volts negative if the oscillator is running. Also, if it is not running it is best to check resistances of the two coils which are part of T401. Philco coils have been known to develop open connections due to corrosion causing wires to break at the terminal connections. Be careful, these are relatively small diameter wires.

If the oscillator coil is damaged beyond repair there are universal oscillator coils available. It make take some work to determine a way to mount a new coil, but it is usually not too hard. A universal oscillator coil is available here. https://www.tubesandmore.com/products/c ... oscillator for $15.

Also you want to confirm the C402B is not shorted due to the plates touching each other. To do this you will disconnect the wire connected to C402B from the oscillator coil at the terminal on C402B (typically this is the smaller gang of the two ganged C402 tuning capacitor) and check resistance with an ohm meter to confirm there is no short circuit. Then you can reattach the wire. Typically if a plate is bent and touching it tends to be one of the rotating plates on the end since it can be prone to being accidentally bumped and bent.

Question, do you have a signal generator and know how to use it? This could come in handy before this is all over. If you end up having to perform an alignment of the oscillator (particularly if a new coil is installed) you may need set of plastic alignment tools. They typically run about $5 https://alphadistributor.net/shop/tools ... kit-5-pcs/ (other sources are available).

Curtis Eickerman

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Mon 06, 2021 10:26 pm 
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Eickerman wrote:
Eevee1 wrote:
Nevermind the oscillator is defiantly broken.
You say this because you definitely are not hearing anything, or because you see something that definitely is "broken"?

Here is the schematic of the portion of the radio that involves the local oscillator.
Attachment:
48-1256 Front End.png
It would be good to check the voltages on the 7A8 which is the Oscillator/Converter tube. Also, though it is not shown, if you are using a high impedance voltmeter the DC voltage at point E should be a couple of volts negative if the oscillator is running. Also, if it is not running it is best to check resistances of the two coils which are part of T401. Philco coils have been known to develop open connections due to corrosion causing wires to break at the terminal connections. Be careful, these are relatively small diameter wires.

If the oscillator coil is damaged beyond repair there are universal oscillator coils available. It make take some work to determine a way to mount a new coil, but it is usually not too hard. A universal oscillator coil is available here. https://www.tubesandmore.com/products/c ... oscillator for $15.

Also you want to confirm the C402B is not shorted due to the plates touching each other. To do this you will disconnect the wire connected to C402B from the oscillator coil at the terminal on C402B (typically this is the smaller gang of the two ganged C402 tuning capacitor) and check resistance with an ohm meter to confirm there is no short circuit. Then you can reattach the wire. Typically if a plate is bent and touching it tends to be one of the rotating plates on the end since it can be prone to being accidentally bumped and bent.

Question, do you have a signal generator and know how to use it? This could come in handy before this is all over. If you end up having to perform an alignment of the oscillator (particularly if a new coil is installed) you may need set of plastic alignment tools. They typically run about $5 https://alphadistributor.net/shop/tools ... kit-5-pcs/ (other sources are available).

Curtis Eickerman

No I just don't hear anything. I do not have a signal generator. I do have alignment tools though.

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Sun 26, 2021 3:18 am 
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I accidentally had the 7C7 and 7A8 mixed up and I only noticed a while after powerup before I did the tests, the dim bulb tester now tests as shorted every time I power on the radio, and the weird speaker noise that I referenced before happens every powerup, do you have any idea how may things may be going wrong? If not, I will go through and check tomorrow.

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Sun 26, 2021 2:57 pm 
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Eevee1 wrote:
I accidentally had the 7C7 and 7A8 mixed up and I only noticed a while after powerup before I did the tests, the dim bulb tester now tests as shorted every time I power on the radio, and the weird speaker noise that I referenced before happens every powerup, do you have any idea how may things may be going wrong? If not, I will go through and check tomorrow.
The first check should be a simple one. With the radio unplugged connect an ohm meter across the power plug prongs and turn the switch of the radio to ON but leave the Phono OFF. This will be just measuring the resistance with the radio turned to ON, but not actually running.

The resistance should be around 250 ohms. If it is near zero, there is a shorted wiring problem.

Curtis Eickerman

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Sun 26, 2021 3:15 pm 
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Ok I will test

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Sun 26, 2021 3:48 pm 
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Its testing around 152 is that good or bad?

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Sun 26, 2021 4:52 pm 
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Eevee1 wrote:
Its testing around 152 is that good or bad?
Well it's not a direct short, but it seems significantly lower than I expected with the Phono turned OFF.

So I would suggest making double sure the Phono is turned OFF (eliminates the motor resistance), and pull out one of the tubes (makes no difference which one) and measure the resistance again.

After you do that remove the dial light and measure it again.

Let me know both readings. The first should be above 2K ohms, and the second one should be extremely high (like the ohm meter is not connected to anything).

Curtis Eickerman

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Sep Sun 26, 2021 5:08 pm 
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Oh and just so you know I did the test on both on radio and phono and both read 152

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Oct Sat 02, 2021 7:14 pm 
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The first test goes past 20Mohms and the second test does the same thing as the first test.

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Oct Sun 03, 2021 4:24 am 
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Eevee1 wrote:
The first test goes past 20Mohms and the second test does the same thing as the first test.
Well, that generally sounds good. It kind of leads me to conclude that there is a short in some part of the filament string. Perhaps a solder splash between filament pins of a tube.

So, here is what I would suggest. With the dial light back in place and the Ohm meter measuring the resistance across the power plug pins and the radio set to the ON position (you should be back to measuring your 152 Ohms or something close), then one at a time unplug each tube and then plug it back in. As you unplug each tube the resistance should go UP significantly. If you unplug a tube and the resistance doesn't rise check the socket for that tube on the underside and make sure the filament lines are not touching and that there are no inadvertent pieces of solder causing an unintended connection.

We're trying to determine if any of the filaments are shorted which would lead to both a lower resistance and prevent one of the tubes from lighting up with filament power.

If you find a problem and correct it I would expect the measured resistance with all the tubes installed to be more like several hundred ohms.

If you still are not finding anything, you might try the dim bulb test once again and see if all the tubes seem to be lighting up and getting warm. There is always the possibility that a loose piece of solder was in there and has fallen out during handling of the radio chassis.

Curtis Eickerman

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 Post subject: Re: Philco 48-1256 repair help!
PostPosted: Oct Fri 08, 2021 10:19 pm 
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Just moving around the dial light causes extreme fluctuations in the resistance.

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