Hum after recap (40-160) - Printable Version

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Hum after recap (40-160) - Stan the Man - 05-20-2016

Ok this will be more of a rant than anything else.. Not really asking anything..
Picked up a rather nice looking 40-160 in an F style cabinet.. I've been looking for one for some time..
All the pieces are there and looked very original under the chassis except for one 8uf electrolytic..
I figured this would be a snap,.. with no cancaps or candohms to fool with, looked like a straight forward re-cap, resistor check,cleaning and few rubber wires bla bla bla...  
So now I have HUM!! NOTHING BUT HUM!! A steady low hum that only changes when touching a screw driver to one side of the volume control(as much probing as I have done) I have traced the schematic until my eyes burn,.. a few times!!
Yes I did figure out that the #6 button has to be pushed in to make the tuner work.. I have not yet started checking voltages as I will need to make up a set of wires to hook up the speaker for testing out of the cabinet.. Also my tube tester doesn't have sockets for these tubes, so....? I'm just like, GRRRRRR!!    
I hate trying to work on something without the proper tools..

As usual, comments and suggestions are welcome.. or maybe just relate a story..

Stan

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RE: Hum after recap (40-160) - Radioroslyn - 05-20-2016

http://www.nostalgiaair.org/pagesbymodel/333/M0013333.pdf

Note that only one of the filter caps - side is connected to the chassis.The other two go back to the ct of the power transformer. If that is OK then try removing tube till the hum goes away. Removing the 84 will kill all sounds. You may have a bad tube with a grid to cathode short. Just for grins try disconnecting one side of 46 the cap across the field coil see if that helps.

Terry

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RE: Hum after recap (40-160) - Radioroslyn - 05-20-2016

Sorry I may have misunderstood your question. I was thinking that it was a hum troublemaker but perhaps it is no signal problem. If this the case then using a signal generator to inject a signal it various stage to determine weather the stage is doing what it is spouses to be doing. With out that checking plate, screen grid, and cathode voltages is the next best thing.

Terry

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RE: Hum after recap (40-160) - Stan the Man - 05-20-2016

Terry , yes I have nothing but the hum.. I'm holding on to the hope its a bad tube.. I hate to buy a set of tubes just because I don't have a way to test what I have,..  Voltage check, YES!! Thank you,.. I will voltage check before I buy tubes.. 

Thanks, Stan

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RE: Hum after recap (40-160) - Radioroslyn - 05-20-2016

I'd say that most of the time the tube are ok if they are lighting up. Yes they could be weak but still functional. I wound suspect a bad connection or resistor before a tube.

Terry

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RE: Hum after recap (40-160) - Stan the Man - 05-20-2016

I'll get it upside down and hooked up so I can poke around some.. I looked for cold joints, but ain't nothing like poking things with a stick..


Stan

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RE: Hum after recap (40-160) - Stan the Man - 05-22-2016

OK OK ok,.. I found out, after driving myself nuts,... the antenna needs to be hooked up to complete the circuit..
So,.. it came to life this morning.. I still had a hum, and no volume control.. no matter how I turned it, the volume control did nothing.. one more look found the center tap dead.. I was able to open the pot up and fix the tiny broken wire..
I gained a volume control and quieted the hum..  As soon as the rubber parts come, I'll finish up..
Maybe an alignment..

Stan

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