NC-270 Ideas needed

[Steve]

I have just picked up  a NC-270 at a ham fest this weekend and I am trying
to breath new life into it. It will power up and It can hear sort of.  There
is a bit of hum when the audio control is set very low other wise you never
hear it, The power supply electrolytic has been replaced since the original
was getting very hot, originally it was 3 sections of 40 uf each and the
closest I could find was 3 sections of 20 uf each, the hum stayed the same
regardless of the change in capacitor value. 

 

There are two things that is does that have me scratching my head.

 

1.	When the radio is on and your are listening to it if you touch the
chassis with anything metal a very loud scratching sound comes out of the
speaker, the  radio has a 2 wire line cord only.  So have no idea what this
is all about.  Does this mean I have some leaky caps in the radio someplace
that I need to find?? 

 

 

2.	The voltages at the power supply are much higher than what the
schematic says they should be. As an example the input to the voltage
regulator tube (OB2) should be 165 volts and I am seeing almost 200 volts,
the output of the OB2 should be 105 and I see well over 150 volts.   The
other voltages are also quite high as well.  Coming from the output of the
5Y3 rectifier there is a 330 ohm 10 watt dropping resistor that connects to
the 1st filter cap.  I have tried making that resistor much higher in value
(800 ohms) and I still have these higher than expected voltages. Any ideas
would be most helpful. 

 

Steve NU0P

 

 


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