NC-270 Progress

[Steve]

I found one of my problems,  I hate to say this but I had the voltmeter in
the AC mode instead of the DC mode.Now that I am measuring DC things look
much better, the OB2 is putting out the right voltage after all 107 volts
and the other voltages are within 20 percent or so, I put a 3 wire plug on
and grounded it but it didn't make any difference with the scratchy noise I
get when I touch the chasses with a screwdriver, still don't know what to do
about that one.

 

  _____  

From: Steve [mailto:stever2k at mchsi.com] 
Sent: Wednesday, August 08, 2007 2:45 PM
To: 'BOATANCHORS at LISTSERV.TEMPE.GOV'
Subject: NC-270 Ideas needed

 

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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