low volume

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low volume

Post by Sinatra1982 on Thu Dec 15, 2016 4:10 pm

Bought this working radio and brought it home. Turned it on and worked great all away round, picked up good and nice and loud. After a couple of minutes or so the volume got low and stays that way.
The low end of dial is low and it is louder at the high end of the dial. This is German 6 tube am fm phono six tube radio. I have the schematic but can't make out everything because the letters are printed in German, however I can read the numbers. I am thinking a bad cap or resistor on the volume control knob. I have only been doing this for a few months. Thanks...

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Re: low volume

Post by terrydec on Sat Dec 17, 2016 4:37 pm

Try inserting a signal into the phono input. That is the audio section. If that is good then look in the front end.

I hope it's not a Grundig.
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Re: low volume

Post by Sinatra1982 on Sat Dec 17, 2016 11:29 pm

It's an Emud Record Junior 186, German radio. I am very new at this and I am not sure how to insert a signal or look in the front end.
I am reading how to books on this and watching videos on youtube, but it isn't sinking in well. I'm turning 68 this month and maybe I waited to long to get into this hobby, but I am going to keep trying. Perhaps you could help me with another problem in another radio.
I have a Philco 48-200-121 that has a burnt resistor that I can't make out the color code. I have the schematic but can't find it on it.
Resistor goes from pin 6 tube 7A8 to a terminal strip. If it's on the schematic I can't see it. I would really appreciate help with this. Thanks...

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Re: low volume

Post by terrydec on Sun Dec 18, 2016 1:15 pm

Welcome to the club. I am 73 and I'm still learning. I would suggest "A Modern Look at Antique Radio Repair" by Alfred Corbin. The book is very good at explaining stuff. It is made so that it lays flat. Mine has smudged thumb prints all over it.
A couple of questions: Do you have an isolation transformer, a signal generator and signal tracer? If not I would definitely invest in these soon. They form the backbone of every serviceman's bench.

One more question, (I sound like Columbo), do you understand the basics of the Superheterodyne function?

Without the schematic I'm in the dark as to your problem. However pin six is on the 7A8 is grid four. I'm think this is the plate of the oscillator. Maybe not. That's why another good thing is a tube manual. Can you pull one end an check the resistor for continuity. Also Philco is known for blocks that contain both resistors and capacitors and can only be accessed by a part number. I usually avoid them.
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Re: low volume

Post by Sinatra1982 on Sun Dec 18, 2016 3:01 pm

I don't have any of this equipment. I have digital volt meter, digital cap tester and a tube checker. I don't understand the Superheterodyne function. If I attached a copy of the schematic could you help with the resistor? No continuity on the resistor. I thought it was a 5 ohm but when I tried one it started smoking and I turned it off. Thanks.

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Re: low volume

Post by Dan Walker on Sun Dec 18, 2016 3:19 pm

You have to have the proper watts rating for the resistor.
If you have a parts list it should give you the wattage rating for the resistors, if not then try a 10 watt resistor. it might be a bit of overkill but at lease you might know if it was the resistor, if it works after you put it in..

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Re: low volume

Post by terrydec on Sun Dec 18, 2016 4:26 pm

If your resistor is smoking then you have another problem. There is a short somewhere. If you can't afford an isolation transformer there is something you can do. Build a light tester. Wire a regular outlet in series with a 60 watt lamp and line cord. When you plug the radio into the outlet the bulb should come on bright for a few seconds and then dim. If it comes on real bright then you have a short, probably an electrolytic capacitor.

Trust me, you need a signal tracer and a generator more than you need a tube tester. Check eBay. Right now you can get most items very cheaply. I got a good Heathkit RF/AF generator for about $20. With a generator you can inject a signal and the trace it through the set. The signal almost always rides the plate current so you have to use a capacitor to block the DC.

I'll try and post a simple explanation of the Superheterodyne circuit later. It took a long time before I understood it, but it is really simple when you strip it down.
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Re: low volume

Post by Sinatra1982 on Sun Dec 18, 2016 7:36 pm

I can tell the resister is a 1/2 watt by it's size. I have a parts list but don't know which one it is, can't find it looking on the schematic.
The schematic does not show one on that pin number. The radio didn't smoke until I put in a new resistor, the resistor itself didn't smoke, it was somewhere else. Would you mind looking at the schematic on line and see what you think. If you like I could email a copy of it. thanks...

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Re: low volume

Post by terrydec on Sun Dec 18, 2016 9:25 pm

I can't really help you with that except for you to look and see it any other part look or smell weird. It sounds like you have a short somewhere.

I am going to try and describe how that Superheterodyne thing works in an off the wall way, so bear with me.  

Forget about mixing and converting signals, that just gets confusing.  Instead- Picture inside your radio a teensy tiny radio station.  It’s true.  This little station is only broadcasting on one frequency, usually 455KH.  Everything else in the radio is made to either amplify, detect, or filter this one signal.  This is because a very intelligent man named Armstrong figured out it would be much simpler to just amplify one radio station than all of them.  
The antenna and tuning capacitor select what broadcast station you want to hear and sends that signal to the mixer/converter tube. Inside that tube the 455 KH signal from your local oscillator, (the tiny radio station), is created and modulated by that incoming broadcast signal.  In other words it all gets ‘mixed’ up in the tube, (That’s not why it’s called that).  The result of all that stuff heads out of the plate over to the IF, or intermediate frequency, transformers and amplifiers. They are tuned to the single frequency, 455 KH, that is also carrying all that other stuff, the RF and AF from the broadcasting station.  After it is properly amplified it is ripped apart and only the pure audio is left.  I know, that is the stripped down version, and there is a LOT of other stuff happening, like where are those darned grid leak resistors located, and what the heck is one anyway?
Just remember that the signal pretty much goes from plate to grid all through the set, with some exceptions. When you can visualize that it becomes simpler.

I hope this helps.  If not blame my dog.  He dictated it.

My apologizes to my peers, (if I have any), for any mistakes or misrepresentations.
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Re: low volume

Post by Bill Cahill on Sun Dec 18, 2016 11:34 pm

Sinatra1982 wrote:I can tell the resister is a 1/2 watt by it's size.  I have a parts list but don't know which one it is, can't find it looking on the schematic.
The schematic does not show one on that pin number.  The radio didn't smoke until I put in a new resistor, the resistor itself didn't smoke, it was somewhere else.  Would you mind looking at the schematic on line and see what you think.  If you like I could email a copy of it.  thanks...

Are you sure it isn't a capacitor?
There were round ones made with one wide band, Five colors.
These were cheap, precision capacitors.

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Re: low volume

Post by Sinatra1982 on Mon Dec 19, 2016 1:12 am

Yes I'm sure it is a resister, it looks just like all the others except it is so dark I can't make out the color of the color coded rings.
I found a picture of the bottom of the same exact chassis that I have but it isn't showing anything on the pin number. Both are a Philco Model 48-200-121. This radio hasn't been worked on before. I replaced all the caps and the radio didn't work so I checked all the resistors and this one had no resistance when I checked with my meter. I then unsoldered one end and rechecked it and same reading.
I have noticed in my short time of working on radios that some of them are different in comparison from what the schematic shows.
Could someone check the schematic and see what they think? Thanks.

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Re: low volume

Post by Sinatra1982 on Mon Dec 19, 2016 1:17 am

Terry, believe it or not but that was a big help. Sounds a lot simpler than what I have been reading in how to books.
Thanks again.

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Re: low volume

Post by Sinatra1982 on Mon Dec 19, 2016 1:53 am

I just found the bottom chassis view of a radio like mine. It has one of those domino mica capacitors where mine has the regular type round type. So Bill maybe you were right. Only problem is it doesn't show the side with the colored dots, it shows the opposite side and it looks all green. I'll keep looking till I can find the right size to replace it with.

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Re: low volume

Post by Sinatra1982 on Mon Dec 19, 2016 3:35 am

Finally figured it out. It is a coupling condenser. It is a 5 mmf, but not sure what to replace it with, I know how to replace a 5 mf but not a mmf. Help please. I know I am slow but I think I am making progress. Thanks.

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Re: low volume

Post by Bill Cahill on Mon Dec 19, 2016 12:02 pm

You need a modern ceramic capacitor of the same value.Do not use a disc capacitor. Five mmf is micro-microfarads. I believe that would be five thousand microfarads.
Not made. Besides, you need a more stable one. I believe it would be five percent. The lower the number, the more stable it is.

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Re: low volume

Post by terrydec on Mon Dec 19, 2016 12:50 pm

Try Antique Radio Supply. They have everything you need.
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Re: low volume

Post by Dan Walker on Mon Dec 19, 2016 1:25 pm

''' Just  Radios'' Sells capacitors, and the shipping is very fast.

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Re: low volume

Post by terrydec on Mon Dec 19, 2016 1:47 pm

Just a note-
Usually you don't have to replace these caps as they hardly ever go bad. And the value is so low that it probably can't be read on a meter. Did you test all of the tubes? This doesn't sound like a cap problem to me; but of course I'm not there.
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Re: low volume

Post by Sinatra1982 on Mon Dec 19, 2016 2:26 pm

I tested it thinking it was a resistor and it tested bad. I had it out trying to tell the colors. Well after figuring out it is a cap and it is a 5mmf I decided to put it back in and now I can't find it. So I'll have to get one. The problem I had before I took it out was that the volume was low, the further you go up the dial it would get a litter louder but still low. I will check the tubes. I have some junk radios with domino type caps. Could I use one of them to replace it with?

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Re: low volume

Post by Bill Cahill on Mon Dec 19, 2016 9:21 pm

I wouldn't advise that. Those caps are paper caps. Inside a mica body. They are no good.

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Re: low volume

Post by Sinatra1982 on Tue Dec 20, 2016 2:38 am

When I order one what do I ask for to replace the 5mmf cap with since they don't make this particular one anymore? Thanks...

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Re: low volume

Post by Sinatra1982 on Wed Dec 21, 2016 5:03 am

Is there a way I can attach a picture of this cap/res? and you could look and see what it is. I found a picture of one like it in the same radio that I have. I have a parts list for this radio but can't find it on the schematic. It is a Philco 48-200 AA5. I can't replace till I find out what it is. It goes from pin 6 of the 7A8 tube to a terminal strip, you can see it all in the picture.

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Re: low volume

Post by Bill Cahill on Wed Dec 21, 2016 10:00 am

You have to take an electronic picture of it, and, install it into your computer under Documents.
Then, you can upload it to your computer to the forum. See the guide on installing photos....

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Re: low volume

Post by terrydec on Wed Dec 21, 2016 1:32 pm

Can you insert photos directly from your computer now?
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Re: low volume

Post by Bill Cahill on Wed Dec 21, 2016 4:51 pm

The owners say yes. But, I haven't been able to.
Read the directions. They say it works.

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Re: low volume

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