Station drifting

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Station drifting

Post by willy3486 on Sun Mar 04, 2012 11:57 am

Hey folks I need some advice for a bright young guy I want to help. I have gotten back into radios again but hope I am on the right track. A young fellow asked me asked me a question on a radio. The radio would play fine but after few minutes the station would drift and change. I am thinking that it is probably in the area from the antenna to the input of the first if transformer. Then if it is not there maybe the If transformers area.

My thinking is probably a wax or oil filled cap first issue then second issue would be tube. I am thinking that any other solid caps like mica caps may be good. I also suggested to inject a signal to the antenna end and trace the signal with a tracer back to the antenna from the speaker. That way he would get some experience of tracking a signal to the source. As far as tubes I said to get a similar radio that works with no drift then swapping the known good radios tubes in to see if issue corrected with a tube swap.

So does this sound feasable on one of the aa5 tube radios? as I said I am a little rusty myself and these would be my steps. The main thing I think is to trace it down the path. I also gave him a generic picture of a radio with areas of waveforms to help assist in tracing down the stages. I think he has a generator and hopefully a tracer. Can anyone add anything or correct my steps if I am wrong?

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Re: Station drifting

Post by Resistance is Futile on Sun Mar 04, 2012 1:55 pm

Sounds like a heat problem. Resistors tend to change value with heat, so check out the oscillator-mixer stage first. Could also be the tuning capacitor with bad solder connections (fractured, cold solder). Does the radio finally settle after a half hour or so? Or does it continue to drift? Moisture and capacitors do change effects. So as the radio heats up it drives out moisture from oscillators and may cause the noted drift. Be sure and clean the chassis of dust and dirt and check for solid and clean solder joints, Tubes may drift if they are weak.
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Re: Station drifting

Post by Bill Cahill on Sun Mar 04, 2012 9:33 pm

While the paper caps need replacing for anything to be reliable, I don't totally agree here.
Tube, maybe. Is this an am radio, of, is this happenning on fm? If it's fm with out afc, there's your problem!
AFC stands for Automatic Frequency Control.
They didn't come out with that until about 1959.
I remember when it first came out. Manny people were complainning about their older fm radios drifting...
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Re: Station drifting

Post by willy3486 on Sun Mar 04, 2012 10:36 pm

I think its just a am 5 tube radio. I heard back today that the boys dad turned it on for a few hours and it did not drift. It sounds like it could be drifting only at night. I have noticed at night I can sometimes have that as well with normal playing radios.

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Re: Station drifting

Post by Resistance is Futile on Mon Mar 05, 2012 1:18 am

You may be referring to radio fading. Radio fading occurs when the signal from the broadcast station is reflected from the Ionosphere. The Ionosphere changes in height during the night so some time you get a signal and slowly lose it, only to reappear after a short time.
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Re: Station drifting

Post by radiopicker on Sat Mar 10, 2012 11:03 pm

Hey guys, finally made an account. Thanks Willy. Radio stopped fading (knock on wood) and dial light stopped flickering with the replacement of the 35Z5 rectifier tube.
Most recent problem as of today is that it's only receiving one station after an alignment. I'm not positive my generator is accurate so I placed a WTB for a frequency counter over at ARF. A nice fellow over there tried helping me measure resistance across the tuning gangs for shorts (which I'm worried may be a problem, although I can't SEE any bent plates), but I didn't understand the process really. Tips on how to do so?

It's a Silvertone 6051 AM radio. Here's the photofact for it: http://www.scribd.com/vmilone/d/83842816-Sears-6051-1 .
One thing after another with this radio, but I won't give up. Thanks.

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Re: Station drifting

Post by Bill Cahill on Sun Mar 11, 2012 3:23 am

Hi. It's really very simple. Put the ohm meter in two spots. One at each section of the hot connections of tuner to frame of tuner. Thats' the other side of capacitor. Slowly rotate the tuner to check for shorts.
Another way with out meter is to have radio turned on. Slowly rotate tuner control. If you hear a scratchy sound in speaker, and, sound cuts out, you have some bent plates.
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Re: Station drifting

Post by willy3486 on Sun Mar 11, 2012 12:36 pm

Thanks guy for helping radiopicker. He is a good teen and reminds me a lot of myself at his age. I had a lot of the TV shop owners helping me at his age and I wanted to pay it forward so to speak and help him. As far as the plates goes how is the best way to straighten them? In the past I used a very thin flat screwdriver but I was wondering if there was a better way. I had even wondered about one of the fin straighteners they use on AC coil fins.

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Re: Station drifting

Post by radiopicker on Sun Mar 11, 2012 1:51 pm

Put the ohm meter in two spots. One at each section of the hot connections of tuner to frame of tuner. Thats' the other side of capacitor. Slowly rotate the tuner to check for shorts.

Let me see if I have this right. So for example, testing the the larger gang. One lead goes to the terminal where there's a wire connected already, and the other lead goes to the terminal opposite that side, where no wire is connected (open terminal)? Is that considered the frame?
And I'm looking for OL or infinite resistance on my meter, which calls for a short, right?

Thanks guys! And good question Willy. You could probably use a cut strip of a credit card, maybe?

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Re: Station drifting

Post by Bill Cahill on Sun Mar 11, 2012 4:19 pm

No, you don't want a short. You want wide open reading.
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Re: Station drifting

Post by Resistance is Futile on Tue Mar 13, 2012 2:14 am

radiopicker wrote:
Put the ohm meter in two spots. One at each section of the hot connections of tuner to frame of tuner. Thats' the other side of capacitor. Slowly rotate the tuner to check for shorts.

Let me see if I have this right. So for example, testing the the larger gang. One lead goes to the terminal where there's a wire connected already,
YES
-------------------------------------------
and the other lead goes to the terminal opposite that side, where no wire is connected (open terminal)? Is that considered the frame?
NO
---------------------------------
And I'm looking for OL or infinite resistance on my meter, which calls for a short, right?
NO!
If the meter is digital then the OL means the resistance is to high to be measured, therefore Over Limit of meter to measure commonly called infinity. Also called No Electrical connection!

Thanks guys! And good question Willy. You could probably use a cut strip of a credit card, maybe?
------------------------------
Answers
1. Start with making sure the radio isn't plugged in.
2. Set your Ohm Meter in the resistance position. Turn on your meter.
3. With the leads disconnected your meter if it has a analog display should show Infinity (no resistance)4. If you touch your meter probes together the meter should move to the opposite end of the scale and show 0 ohms (or very close to it) that means you have continuity (or a complete electrical path)-------------------------
On your radio you usually have 2 sections of variable plates, one section is for the oscillator (smaller or less number of plates) and the antenna or R.F. section with larger or more plates.

On most variable caps you have one wire for each section, however you may have two electrical tabs on each section on opposite sides of the cap.

With your ohm meter take one lead and touch one section of the tab and the other probe to the frame of the capacitor.
Rotate the capacitor knob while looking at the meter face. If the meter moves from the infinity position to 0 ohms you have a short, if you do, note the position where this occurs. That is where the plates are shorted.

Now do the same with the other section in the same manner.
Note you may have some resistance showing during this test, because of resistors and coils that may be also connected. If this is the case, just look for a total short while moving the cap back and forth.

If you find a Short then you have to make sure you slowly adjust the cap movable fins that are touching.
When you have done this you should not be able to see any contact between the stationary plate(s) and the movable plates.
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Re: Station drifting

Post by Brig on Wed Mar 14, 2012 7:01 pm

If it's drift, when all else fails, change the oscillator coil. This assumes, of course, that you have checked/replaced the oscillator resistor and the oscillator cap (usually a mica).

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Re: Station drifting

Post by radiopicker on Fri Mar 23, 2012 5:14 pm

With your ohm meter take one lead and touch one section of the tab and the other probe to the frame of the capacitor.

Whenever I hook a lead to the "frame" I get a reading of about 4.7 Meg ohms. No matter where I hook it up, I always get that reading. Why is this? I mean the frame is the wall on either side of the cap, right?

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Re: Station drifting

Post by Bill Cahill on Fri Mar 23, 2012 5:19 pm

No, it's not. And, you can't properly check a capacitor with an ohmmeter.
They should show infinity.
Caps don't read like resistors.
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