Post by John-Del Post by John-Del Post by Peter Wieck
There are two schools on the RLC - I choose installing MOAR
aluminum-finned power resistors to caps - 28 flavors of ice-cream and
There's no room. This is a very tight layout. The footprint is 4" X
10" by eyeball. I'll post a picture of the chassis when I can. I
can't see it dissipating that much heat without destroying the cabinet.
OTOH, since it has no cabinet...
Post by Peter Wieck
First IF can?
Cap pretending to be a resistor under load?
Short between sections in tuning cap?
It will be something that is operational *ONLY* when the 6A7 is conducting...
Peter Wieck Melrose Park, PA
I've checked all of those things. All caps are new and have been
rechecked for value and leakage. Most resistors were out of tolerance
and replaced, and those have been rechecked for value. My best guess
right now is that the original osc did fail and I somehow miswired it
when I reinstalled both the rewound coil and subsequently it's
replacement. I did a quick review by schematic and I was pretty sure
right now, but since none of this makes sense, I can't think of
anything else unless my donor coil, despite reading proper resistance,
is also bad! I'm going to redraw the osc coil terminal out and check my
wiring one more time.
Last plan is to disconnect the antenna input side from the tube to see
if it will oscillate.
John Wolcott, CT
Okay, I'm at a dead end here. I've redrawn the oscillator coil diagram
and confirmed that I wired the coil in correctly. I've reconfirmed that
both my rewound osc coil and my donor coil are reading normal continuity
on both windings and have no leakage between them. Every resistor,
capacitor, and padder are right where they need to be in the oscillator
circuit. The 6A7 socket is clean, tight, and I read no leakage between
the pins. Counting the tube socket and tuner, there are 11 parts in the
local oscillator, and it's defying all my attempt to make it run.
I removed the gang tuner and checked the padder caps/micas on both
sections, and they're fine. The tuner swings 25 to 500 pf on both the
osc and rf sections opened to closed (sections look physically identical
and read the same). I ran 600 volts across it looking for any leakage
or arcing, and there's none. I cleaned it up a bit for aesthetic
reasons, readjusted the back screw to better center the vanes, tested it
once more for value and leakage, and will reinstall it next week. Even
the gum rubber washers are perfect.
I've now tried 4 6A7s and none work. Coming full circle, I'm back at the
oscillator coil. These coils are some 80 years old - any chance
they've trapped some moisture? Anyone baked the crap out of these to
solve a stubborn oscillator issue? The top lead of the coil is running
between the coil form and the can. Is this right or should the top coil
lead run down *through* the coil form, or does it not matter. Any
chance playing with the cathode resistor value can help?
I'm going to try giving the coil a couple of days in a hot box and see
what happens, but my next plan is to either replace the oscillator coil
with a universal or change the converter tube to a later type. For the
former, does someone make a universal coil that will fit the 60 directly
without changing other parts?
Thanks for reading through all of this!
John Wolcott, CT
when the tube in) or if it requires the tube to be operating.
The coils have to be phased correctly or the oscillator won't work. This
won't explain the initial failure but could be an issue with later work.