[Hallicrafters] SX-101 Problem

[Mark Shaum]

Bob,

Your oscillator isn't oscillating.  Have you checked V3 via tube
replacement?  Tube testers sometimes don't tell the full story on an RF
oscillator tube.  The osc grid (pin 2) would definitely read negative if
the stage is oscillating, as long as you are using a meter like a VTVM
or other that does not load down the circuit much when you are probing.
Most old VTVM's switched a  1 meg resistor in series with the tip right
at the probe for DC measurements to provide a good degree of isolation.
Do you hear any change in output of the set as you probe the oscillator
grid?  If so, your meter may be loading the circuit down to the point
where it wont go.

Since you appear to have no oscillator output on all bands, you should
focus on a component of the HF osc that is common to all bands.  Cathode
bypass C126, maybe the ceramic or mica C62 or C63, also check continuity
from the oscillator coils through the bandswitch until a coupling
capacitor is reached. You should measure near zero ohms, everything in
the switched inductor area is grounded.

The low filament voltage is strange if B+ is ok, but I think the 12AU7
would still oscillate with 5.5-5.75 volts on them.  The filaments of the
set are fed through the rear panel octal socket with a jumper in the
plug for the filaments between pins 6 and 7, perhaps you have a high
resistance contact there.

Keep us posted!  Mark K9TR

----- Original Message ----- 
From: "robert Keeble" <kg4nvx at igiles.net>

 V3 12AU7A 1st Conv. Osc./ Cathode follower All ok except Pin 2 grid
chks
 0 vdc (calls for -12V) and Pin 7 grid chks -2V (calls for -4V)