**SOLVED**another Philco 38-12

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**SOLVED**another Philco 38-12

Post by Ben Delk on Sat Dec 29, 2012 12:20 pm

http://www.nostalgiaair.org/Resources/236/M0013236.htm

Picked up another Philco 38-12. I have replaced all the caps and out of tolerance resistors but all I’m getting is “white noise”. The 'white noise' does increase with volume control in the higher range.
I have measured all the tubes values as follows:
All heaters > 6.4
Output( 41) pin2> 192, pin3> 210, pin4> 11, pin5&6>0
Rect (84) pin2> 112, pin3>105, pin4>270, pin5> 0
2nd dect\1st audio (75) pin2> 87, pin3>2.5, pin4> 2.5, pin5> 2.3
1st IF (78) pin2> 209, pin3> 38 should be 90, pin4&5> 0, pin6> -1
Dect\octl (6A7) pin2> 207, pin3>38 should be 90, pin4> 190, pin5>340, pin6> 0

1st IF trnf >, 8 ohms and 13.5 (specs 11)
2nd IF trnf>, 23.5 (specs 22)ohms and 4 ohms

Suggestions?

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Re: **SOLVED**another Philco 38-12

Post by Wildcat445 on Sat Dec 29, 2012 2:19 pm

I don't see any negative voltage on the grid of the oscillator. I don't have the schematic in front of me, but my guess/suggestion would be to start with the oscillator section. Try the old "listening to another radio" trick to see if the oscillator is working in this one. You need to find out why you have improper voltage on the IF amp and Osc/det tubes. Out of range resistors (?) even though you have replaced them. Maybe a bad connection somplace ? Maybe a miswire someplace? Double check your work, since it happens. Subbing the 6A7 is a good idea, since converter tubes have been known to be good, yet still not work in a given circuit. BTW, do you have an antenna on this set? I am sure others will chime in with good ideas as well.

Regards

WC

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Re: **SOLVED**another Philco 38-12

Post by Resistance is Futile on Sat Dec 29, 2012 7:39 pm

My suggestion is check

.03 mfd cap
part # 10 on the schematic for a short.
And check

the 40,000 ohm resistor for value
# 11 on the schematic.
Note :
These are connected to the pins #3 on both tubes 78 and 6A7

Since the other voltages are close to what they should be.
That cap may be or, is shorted or partially shorted dragging the voltage down or that resistor is off in value. Or a combination of shorted cap and overheated resistor from short. My Opinion anyway.

Just as a suggestion, so please don't be offended.
I think if you list each tube first on a separate line and the list the pins tested below and in order it would make it easier to follow.
As an example using your list and by modifying it to show what I mean.

I replaced the Greater than symbol because that states that the voltages are greater than, and that can cause confusion.
--------------------------------------


I have measured all the tubes and the voltage values are as follows:

All heaters = 6.4 Volts
Output( Tube # 41)
pin2 = 192,
pin3 = 210,
pin4 = 11,
pin5 & 6 = 0

Rect (Tube # 84)
pin2 = 112,
pin3 = 105,
pin4 = 270,
pin5 = 0

2nd dect\1st audio (Tube # 75)
pin2 = 87,
pin3 = 2.5,
pin4 = 2.5,
pin5 = 2.3

1st IF (Tube # 78)
pin2 = 209,
pin3 = 38 should be 90,
pin4&5 = 0,
pin6 = -1

Dect\octl (Tube # 6A7)
pin2 = 207,
pin3 = 38 should be 90,
pin4 = 190,
pin5 = 340,
pin6 = 0
---------------------------------
Resistance measurements taken:
1st IF trnf = , 8 ohms and 13.5 (specs 11)

2nd IF trnf = , 23.5 (specs 22)ohms and 4 ohms

Now this would allow me to print the list out and I could put notes on the side of each to help me (such as check or OK, or list the manufactures voltages for comparison checks etc.)
Again it would help us if all would follow a similar format. Thanks!
Please follow up on this, with your discovery and results of troubleshooting.



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Re: **SOLVED**another Philco 38-12

Post by Dr. Radio on Sat Dec 29, 2012 8:47 pm

Excellent advice Cliff. Cool
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Re: **SOLVED**another Philco 38-12

Post by Ben Delk on Sun Dec 30, 2012 9:41 am

Thanks for the advice guys, I'll check on these suggestions later today.

Cliff, no offense taken Smile . I actually started with that format but decided saving space might be easier to read scratch . Thanks
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Re: **SOLVED**another Philco 38-12

Post by Resistance is Futile on Sun Dec 30, 2012 2:51 pm

It was just too hard to remember with them all lined up without any breaks. Especially when going to the schematic and then trying to remember where I left off on the list. Cool
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Re: **SOLVED**another Philco 38-12

Post by Ben Delk on Sun Dec 30, 2012 9:02 pm

Philco is working now. I resoldered all the connections and remeasured all the caps and resistors (ok). Found the 110 mica cap (part 6 on the schematic) connected to 6A7 had varying readings when I moved it. Replaced it. Powered up and got a breif radio station come in so I started wiggling the tubes a bit. Moved the 78 tube and the noise stopped and had a breif broadcast signal then stopped. Upon closer inspection of the IF 78 I found pin 3 socket had a broken pin connector. Replaced the pin socket and it works.
Thanks for the help and suggestions which led me to the this fix.
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Re: **SOLVED**another Philco 38-12

Post by Bill Cahill on Sun Dec 30, 2012 9:45 pm

Congrats, Ben. You are learning well!!!!!
Bill Cahill

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Re: **SOLVED**another Philco 38-12

Post by Resistance is Futile on Mon Dec 31, 2012 1:19 am

Glad to Hear you found the solution, I will Mark this as solved!
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Re: **SOLVED**another Philco 38-12

Post by Ben Delk on Sat Jan 05, 2013 5:56 pm

Philco 38-12 complete. This radio started out ugly white. Most of this models you see have oak veneer but this one has a maple veneer with factory white.



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Re: **SOLVED**another Philco 38-12

Post by fixinmyphono on Sat Jan 05, 2013 6:26 pm

looks good!
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Re: **SOLVED**another Philco 38-12

Post by N7ZAL on Sat Jan 05, 2013 7:53 pm

Very nice!
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Re: **SOLVED**another Philco 38-12

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