NC300..ASLEEP..HELP..

[ve6pg]

 :'(HI FROM TIM..DONT KNOW WHAT HAPPENED,NO T-STORMS IN THE AREA,BUT MAYBE A LARGE STATIC BURST TOOK OUT MY NC300..ALL TOOBS CHECK OK.NO TRANSMITTING WAS GOING ON. I TURNED ON THE RECEIVER THIS EVENING,AND ASIDE FROM LOW VOLUME,I'M HEARING NOTHING..NOT EVEN THE CALIBRATOR. PULLED ALL THE TOOBS,CHECKED THEM.OK..SO I WAS THINKING A STRONG BURST OF SOME KIND..WHAT SHOULD I BE LOOKING FOR,IN ORDER TO REPAIR HER?SO,THERE ARE NO SIGS OF ANY KIND,ANTENNA NOT SHORTED,ETC..IDEAS?..SK..

[w3jn]

You say low volume... but also say "nothing".  If it is completely dead, I'd suspect either of the following:

1)  Believe the NC300 has a 4H4C ballast tube which 'regulates' the oscillator filament current.  If it dies the oscillator tube also dies.   It should get fairly warm in operation... if it's stone cold it's bad.  Replace it with an old 6V6 as that tube is almost unobtainium these days.

2)  I had an audio output xformer go bad in a NC303 I had.  I replaced it with a Radio Shack  110/6.3V filament transformer and it sounded fine.

3)  B+ Voltage OK?  The OA2 regulator tube glowing?

Do some checking and let us know, we can go from there.

73 John

[ve6pg]

..JOHN..LOW HISS AUDIO,NO SIGS OF ANY KIND. 6V6 IS IN THERE,AS A REPLACEMENT,OB2 IS FINE.EVERYTHINGS LIGHTS UP,AS  IT SHOULD,BUT THAT'S IT.ALMOST LIKE NO ANTENNA.I USED TO HEAR A SCHRATCHY SOUND,WHEN I CHANGED BANDS,NOT NOW.  I KEYED-UP A TRANSMTTER ON 75AM,INTO A DUMMY LOAD,NO SIGS ARE DETECTED...SK...

[w3jn]

I'd look for a problem with the second oscillator or lower freq IF stages.  If you have a scope and sig gen this is easy.  If all you have is a meter, compare voltages with the voltage chart in the manual.  If a voltage is too low then something's drawing too much current - suspect a bypass cap.  If a voltage is too high you have an open resistor somewhere or a tube that's weak (not drawing enough current).

73 John

[Jim, W5JO]

A scope really makes it easy Tim.  If you don't have one, do as JN says.  You can use the calibrator for a signal gen.  Then compare voltages to the voltage chart in the manual.  Any tube that is not drawing current will have a higher voltage level.  Did you try touching the grid of the first audio tube to see if you hear hum.  Use a probe to do that.  If you do, then do the same all the way from the back of the radio to the front. 

When you touch thegrid  leads of the tubes, you should hear a slight pop.  When you don't hear one, check that stage, then work your way to the front end.

Good luck!

[WA1HZK]

I have had several similar crap outs in my 303 over the years and I can usually find it by checking the voltages on every tube socket. Screen Bypass caps short out. Brent had an open wire in the RF Amp transformer thus no voltage on the plate. It's gotta be something like that. Get a big coffee on a morning you can dedicate to it and you will find it. If you have weird voltages & cannot figure it out, post the readings here and we will all hit the schematics with you.
Keith
WA1HZK

[ve6pg]

..ok..all fb now..rf amp was taken-out,by  something..dont know what,no t-storms,tx was not on,so t/r relay didnt fail...replaced all the tubes,and many burned resistors and caps.did a complete alignment,,and it's werking better than ever..all voltages up to spec..too bad i didnt have any paint to touch up the cabinet..sk..

[Jim, W5JO]

Great news Tim!

[WA1HZK]

Yah
See, No sweat, it was those damm Gremlins!