02-20-2017, 08:07 PM
I am nearly finished restoring a 1936 Philco 60, the last version before
the model 37-60. I'll leave the details of the restoration at the end of
this post. The problem is the oscillator does not work and the radio is
mostly quiet after applying power, however, I can "jump start" the
oscillator and the radio comes to life. When not oscillating, the screen
grid on tubes 6A7, 75, and 78 are very low about 10 to 15 volts and
resistor #14 (32k ohm) gets very hot with a voltage drop of 260 volts
which is near its 2 watt limit. When it is oscillating and working
properly, the screen grids are about 60 to 70 volts and resistor #14 is
about 150 volts. On a weak station, the radio will play for a little
while then the oscillator will cut out. But, a "jump start" will bring
the radio back.
What is weird is that I can "jump start" the oscillator. To do this, I
have unsoldered the lead to capacitor #13 and the output of the
oscillator coil and reconnected it with a jumper cable. This was done to
see if I wound the output coil backwards. I noticed when disconnecting
then reconnecting the jumper would break the silence on the radio. I
think that bit of static from reconnecting the jumper would kick start
the oscillator. I can then power-off the radio briefly, and turn back on
(within the time the filter caps have not fully discharged). Does
anyone know why this is happening? I can't figure out a fix for this.
The attached schematic will show a red oval around where the jumper is
applied. I can provide a video on Youtube if anyone wants to see this.
In the restoration, the radio was re-capped. The two 8 MFD filter caps
were replaced with 10MFD caps. The bakelite condensor blocks were all
re-built with new caps. The multi caps in the metal can were replaced by
a terminal strip with appropriate caps. The shortwave portion of the
antenna coil (approx 0.7Ω) was re-wound, and the 3.4Ω portion of the
output oscillator coil was also re-wound thanks to the information from
this Phorum and other Philco sites. Initially, the 8MFD filter caps were
replaced with 16MFD caps, and thinking that possible the oscillator
needs some slight ripple to start, we have since replaced the 8MFD
filter caps with 10MFD. There was no change to the oscillator. I've
since went back to the 16MFD filter caps.
the model 37-60. I'll leave the details of the restoration at the end of
this post. The problem is the oscillator does not work and the radio is
mostly quiet after applying power, however, I can "jump start" the
oscillator and the radio comes to life. When not oscillating, the screen
grid on tubes 6A7, 75, and 78 are very low about 10 to 15 volts and
resistor #14 (32k ohm) gets very hot with a voltage drop of 260 volts
which is near its 2 watt limit. When it is oscillating and working
properly, the screen grids are about 60 to 70 volts and resistor #14 is
about 150 volts. On a weak station, the radio will play for a little
while then the oscillator will cut out. But, a "jump start" will bring
the radio back.
What is weird is that I can "jump start" the oscillator. To do this, I
have unsoldered the lead to capacitor #13 and the output of the
oscillator coil and reconnected it with a jumper cable. This was done to
see if I wound the output coil backwards. I noticed when disconnecting
then reconnecting the jumper would break the silence on the radio. I
think that bit of static from reconnecting the jumper would kick start
the oscillator. I can then power-off the radio briefly, and turn back on
(within the time the filter caps have not fully discharged). Does
anyone know why this is happening? I can't figure out a fix for this.
The attached schematic will show a red oval around where the jumper is
applied. I can provide a video on Youtube if anyone wants to see this.
In the restoration, the radio was re-capped. The two 8 MFD filter caps
were replaced with 10MFD caps. The bakelite condensor blocks were all
re-built with new caps. The multi caps in the metal can were replaced by
a terminal strip with appropriate caps. The shortwave portion of the
antenna coil (approx 0.7Ω) was re-wound, and the 3.4Ω portion of the
output oscillator coil was also re-wound thanks to the information from
this Phorum and other Philco sites. Initially, the 8MFD filter caps were
replaced with 16MFD caps, and thinking that possible the oscillator
needs some slight ripple to start, we have since replaced the 8MFD
filter caps with 10MFD. There was no change to the oscillator. I've
since went back to the 16MFD filter caps.
