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City: Clayton, CA
Hello,
I'm pretty inexperienced when it comes to old radios, but I'd like to try and fix a problem with my PT 7 set. I had this set recapped and had any out of spec resistors replaced by radio restoration person that was recommended to me locally. The radio has worked well for a few months with infrequent use. It always played fine for the couple of hours I would turn it on. The sound actually seemed to improve the more frequently it got used so I was pretty happy. Last night I turned it on and it played well for about 20-30 minutes and then the volume slowly faded out. I was able to turn the volume knob up a little and it played for another 5 minutes or so and then it faded again. I turned the radio off for a few minutes and then back on. Now it seems to have a set limit on volume. I can turn it on and it warms up and it turns up to a certain point and then turning the knob past that has no additional effect on volume? Any advice on what to start looking for? I'm thinking maybe the output tube? Thanks for any help.
Karl
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Karl
Welcome.
Without plunging deep into it right now the first thing I would do is testing the tubes.
All of them.
Or if you have extras, replace one by one.
Can be something else but tubes is the first choice.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 6
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City: Clayton, CA
(05-07-2016, 09:41 AM)morzh Wrote: Karl
Welcome.
Without plunging deep into it right now the first thing I would do is testing the tubes.
All of them.
Or if you have extras, replace one by one.
Can be something else but tubes is the first choice.
Hello,
I went ahead and ordered a set of tubes for the radio. I don't have access to a tube tester so, so replacing them one at a time with tested good tubes is my next best option. I'll know in a few days if that does it. I know I also know that I'll need a new volume switch at some point, but I don't think that has anything to do with this problem.
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Welcome to the Phorum!
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I have a nice serviced Philco Hippo, pilot light blinks last nite, the fades, then nothing, so try the ouput and the rectifier tube.
Output was shot, change it out and beautiful music.
Paul
Tubetalk1
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City: Clayton, CA
I have a new set of tested tubes now. Changing the output changed nothing. I have a feeling it may be the volume control itself. When I turn the radio on now the volume is constant. Turning the knob doesn't change anything. The sound itself is very clear and the reception is good. I went ahead and ordered a new control. We'll see if that helps before I dig too much further.
Karl
Posts: 16,507
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Could be.
But before ordering you could've take a meter and simply see if the pot is functional, by measuring 1) end-to-end, (is this the 42-PT7? then it should be 500k or around, some deterioration manifested as a rise in value is OK) and 2) measuring the wiper (midpoint) to either end while rotating the shaft, seeing if the resistance changes from very low to the max without any interruption.
Also the pots are easily (usually - I just had one exception with one of the Kirk's radios) taken apart, so you can unbend those small tabs, open it, spray it with Deoxit, put a small dab of white Lithium grease mixed with deoxit on the scale, spread it by rotating the shaft and in most cases you have a perfectly good volume pot again.
Especially considering you will likely get a used pot, that also might require cleaning, unless you do know it is a NOS item. Which also could have an oxidized wiper.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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(05-08-2016, 05:53 PM)klondike98 Wrote: Welcome to the Phorum!
+1
Terry
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http://www.nostalgiaair.org/pagesbymodel...013568.pdf
Something else to look at is the AC voltage from pin 1 of the 35Z3 to pin 8 of the 7C6. Should see about 103vac or little higher when set is operating properly.
This voltage comes from the ac line and goes though that resistor that is riveted to the chassis. It powers the heaters ( the part that lights up) in the tubes and should be pretty constant without fluctuation.
As with any set w/loctal tubes pins and sockets are suspect for bad connections.
To check the volume control the hear if it is limiting the volume hook a jump from the center post to the post on the left. What this does is the same as tuning the volume full up.
Have fun!
Terry
Posts: 6
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City: Clayton, CA
Hello,
I finally got a new volume control and got some time to swap it out over the weekend. It seems to have fixed the issue. The only problem I'm having now is the radio seems to have more background static than I remember. It downs't change with volume, it is just a really crunchy sounding static in the background. I'm happy to get this thing working agin though.
Karl
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