NC-270 Progress

[Bob Krassa]

Steve, the schematic shows a line to ground capacitor on the power cord side 
of the transformer primary.  If that capacitor has an internal short, or 
leakage, then your chassis may be somewhat hot.  I would replace that 
capacitor with a modern X or Y capacitor - can't remember which is X and 
which is Y - but see http://www.justradios.com/safetytips.html

That would explain your scratchy sound.

Also, the black or hot wire in the power cord should be connected to the 
switch side of the transformer primary, and the white wire to the side of 
the transformer primary where the said capacitor is located.

Remember the old rule to keep one hand in your pocket when working on a live 
set.

73 Bob Krassa KC0TDS

----- Original Message ----- 
From: "Steve" <stever2k at MCHSI.COM>
To: <BOATANCHORS at LISTSERV.TEMPE.GOV>
Sent: Wednesday, August 08, 2007 4:37 PM
Subject: Re: NC-270 Progress


>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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