[Boatanchors] National NC-300 HF oscillator problem

[Philip Atchley]

Hi, Me again,
I'm working on a National NC-300 Hamband receiver for a friend.  It was
given to him by a gentleman who couldn't get it to play.  He thought "maybe"
the HF oscillator for the first mixer wasn't working.  My friend Don,
(W6LRG) tried also, but isn't a "strong" technical type, so he brought it to
me for repairs.  He also asked me to re-cap it for him along with anything
else it might need.

Anyway, when I first got it here I confirmed that apparently the first LO is
"dead".   I tried the usual, replacing the 6AH6 tube (twice), checking tube
Voltages etc.   I also used a digital portable radio to "look" for the
oscillator 2215KC both above and below the operating frequency (1st IF is
2215KC) on a number of bands.  No signal detected.

1.  Plate Voltage is quite low, 30 Volts instead of 69.  Plate resistor
(10K) is in tolerance, coupling capacitor to the mixer was disconnected in
case it was leaky.  No effect on plate Voltage.  I suspect plate Voltage is
low because the oscillator isn't oscillating and hence has no grid bias
developed, leading to high plate current.

2.  Screen resistor is in tolerance, Screen Voltage in tolerance.

EVERYTHING in the (fairly) simple circuit has been either checked or
replaced.  I even reached WAY under the bandswitch and replaced the 15pF
grid capacitor leading to the tank circuit (NOT an easy task).

Is anybody aware of a common failure mode in the oscillator of this
receiver.  There REALLY isn't a lot of components in that circuit!

73 from the "Beaconeers Lair".
Phil, KO6BB

DX begins at the noise floor!
Merced, Central California
37.18N  120.29W  CM97sh