655 SW band - Printable Version
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655 SW band - BrendaAnnD - 09-25-2014
I've got this set 90% restored electrically, but am having one last issue with it. The SW band will not track at the bottom, no matter what I do with the adjustments. It gets as close as I can get it (6 MHz shows as 6.2 MHz on the dial) with the lower end compensator cap pretty much fully open. The high end tracks pretty well, down as far as about 8 MHz or so, then gets progressively more off.
Any ideas?
TIA
RE: 655 SW band - morzh - 09-25-2014
Brenda
I had similar problem with 38-15, happened to be the pentagrid.
Have you tried to change the osc tube yet? The 6A7?
RE: 655 SW band - Chuck Schwark - 09-25-2014
Off top of head:
Weak tube as Morzh just stated
Bad mica or missing/splits layer(s)
Corrosion/tarnish in/on trimmer plates or screw
SW osc coil may have "green" wire problem not visible under wax
Wiring in this section may have a intermittant break or "green" under insulation
Moisture in SW osc coil
RE: 655 SW band - morzh - 09-25-2014
Chuck, you are scaring her! (not that she is easily scared).
Brenda, in the morning it will magically work all by itself.
RE: 655 SW band - Chuck Schwark - 09-25-2014
Brenda is MIL-spec, so she can take it.
Chuck
RE: 655 SW band - BrendaAnnD - 09-26-2014
Oh, the radio works a charm.. it's just that low end of the SW dial. Swapped in another 6A7 tonight, didn't change much, if anything, it got a little further off. Still great reception. If I wasn't a perfectionist when it comes to dial calibration, I'd just leave it at that. Will try cleaning the trimmer and see what happens. I'd hate to have to pull that coil, this one's the nastiest Philco I've ever seen for coils. Someone changed the coil in the mixer section some time ago, and it looks like they just cut the wires off long enough so they could splice in the replacement coil.
RE: 655 SW band - AI2V - 09-26-2014
Have a close look at the plate spacing in the tuning condenser; a near short in the tuning condenser will effect every band but at 6MC you might just have run out of adjustment.
More realistically I would spread the turns on that band's oscillator coil. Don't be afraid to do it, it's something that I do often when I want a perfectly tracked dial.
RE: 655 SW band - Chuck Schwark - 09-26-2014
Brenda,
Just had another thought -- lead dress to that SW coil could be something to look at.
If there was previous "messing around" right there, wire routing could be compromised.
Maybe the leads to the SW coil are reversed?
Leads to the coil being a little too long can alter the inductance a bit as well.
Chuck
fine post - waseem123 - 09-30-2014
adjustments. It gets as close as I can get it (6 MHz shows as 6.2 MHz on the dial) with the lower end compensator cap pretty much fully open. The high end tracks pretty well, down as far as about 8 MHz or so, then gets progressively more off.