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crosley:  ; 66CP (66 CP)

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » crosley:  ; 66CP (66 CP)
           
Dave Turner
 
 
USA  Articles: 52
Schem.: 8
Pict.: 17
16.Mar.09 20:57

Count of Thanks: 9
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I've been replacing capacitors on this chassis, so far all the electrolytics, and several wax/paper.  I found and replaced a 1,000 ohm, 10 watt resistor shorted out, Part no. 39371-5, and item #13 on the schematic.   I have also tested all the tubes.

Initially, before any repairs, I could get no sound at all from this set.  Now, after the above mentioned repairs, I get a slight hum when the power is on,  and then, when the power is turned off, I get a distinctive louder hum which quickly diminishes to nothing.??

I'm new at this game, and don't have any test equipment except an ohmeter and a Precision 912 tube tester!

Any thoughts or suggestions would be greatly appreciated.

Dave

 

Thomas Albrecht
Thomas Albrecht
Officer
USA  Articles: 384
Schem.: 6679
Pict.: 682
16.Mar.09 23:32

Count of Thanks: 3
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Dave,

Since you now have a hum, you've made some progress.  Replacing the burned out 100 ohm resistor has restored power to your 1st audio amp and RF stages.  Based on your description, it sounds like the audio amplifier may now be working.

The next two steps I would recommend:  Test the audio amplifier by turning up the volume all the way, and touching the tip of a screwdriver to the center lug of the volume control.  If you get a louder hum when you do that, the audio amplifier is generally working.

To troubleshoot the remaining stages with the equipment you have, I would recommend that your next step be to check the voltages on the tube pins and compare to the "socket voltage chart" you see at the bottom of the schematic on page 15-19 of Rider (available at Nostalgia Air or possibly on one of the schematics available here for this model -- for some reason I cannot open two of the schematics here right now).

Check the voltages on each of the socket pins for which a voltage is shown.  When making these measurements, the negative lead of the voltmeter connects to the chassis, and positive lead to the point being tested.  Note that most of the measurements are DC, but those marked with asterisk are AC (filament voltages).  If any voltage is more than 20% off target, you might suspect that a nearby component has a problem.  If you can't find the particular problem, report back here which voltages are off, and someone here can help discern what the cause is likely to be.

If your audio amplifier is working, you should focus mainly on the voltages for the 6SA7 and the two 6SK7s (the RF, mixer, and IF stages), although while you're in there making measurements, you might as well check the voltages on all the tubes.

Best regards,

Tom

Dave Turner
 
 
USA  Articles: 52
Schem.: 8
Pict.: 17
16.Mar.09 23:52

Count of Thanks: 4
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Tom,

I really appreciate the help.  I'll try the steps you recommend and let you know how it goes.

Dave

Dave Turner
 
 
USA  Articles: 52
Schem.: 8
Pict.: 17
17.Mar.09 00:52

Count of Thanks: 4
Reply  |  You aren't logged in. (Guest)   4

Tom,  Hey, it's working.  I tried the screwdriver on the volume control and it does get louder.  But, in the process I found a very noisy volume control switch.  Probably dirty, creates a lot of static and intermittent volume variation.  I will give it a good dose of contact cleaner.

I did check a few tube socket voltages, but after I got this thing going I did not proceed.

I connected a very short loop antenna, and receive several stations.  I'm sure with a good antenna it will be much more receptive.

Again,  I sure do appreciate this site and the generous help you all provide.  Maybe someday, I'll be able to reciprocate.  Right now, I'm learning.

Dave

  
rmXorg