42-761EZ Chassis Restoration - Printable Version
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RE: 42-761EZ Chassis Restoration - Paul Philco322 - 02-17-2013
Sweet Dial, That is going to look so cool in a dark room, pull the "black out curtains"
Paul
RE: 42-761EZ Chassis Restoration - Ron Ramirez - 02-18-2013
Curiouser and curiouser... (edits in bold italics)
AM - Dead. Faint signal from generator heard at 1500 kc but trimmers have no effect.
SW 1 - Works fine. Aligned up fine.
SW 2 - Works from low end (7.3 mc) to just above 12 mc where the oscillator drops out. Working fine. Aligned up fine.
31M - Works from low end (9.3 mc) to about 9.5 9.8 mc where the oscillator drops out. 9.7 comes in around 9.5 on the dial. Any attempt to move the signal higher with the proper trimmer makes the oscillator quit, so I suspect a bad trimmer here.
25M - Dead.
19M - Dead. Will not respond to signal from signal generator but it is picking up a few stations very faintly.
16M - Dead.
13M - Seems to be working; picked up one very weak station around 21.7 mc. Aligned up fine on this band.
I'll have to study the schematic before proceeding.
RE: 42-761EZ Chassis Restoration - Chuck Schwark - 02-18-2013
Sneak low impedance leakage in osc tube socket or in the bandswitch wafer(s)....crud/dust/?? Clean with Q-tip with isopropyl alcohol, NOT dexoit which leaves behind oily anti-corrode residue. Maybe hard to see or get at both side of each wafer and between stationary contact lugs? I assume you have checked for and eliminated the Philco Coil Greenies and the osc tube is good.
Maybe a marginal osc tube? Tried a swap? You'd think AM would oscillate if SW bands do, somewhat.
'tis curious...
Chuck
RE: 42-761EZ Chassis Restoration - Ron Ramirez - 02-18-2013
I just ran through the alignment procedure and edited my comments appropriately in my previous post above.
Chuck, the 7J7 det-osc tube I put in the radio is NOS, the 7J7E that was in the set tested very weak. I think I may have another, and could try another...
I have not tried cleaning the band switch, and yes, I should do so.
There is a lot of rust on top of the chassis. Could be mouse urine? Maybe many/most of the trimmers, most of which are on top of the chassis, could have suffered damage as a result? If so...this could become a shelf queen upon which I wasted a lot of time. Parts for these babies are near-impossible to find, as the sets themselves are quite rare in this country.
RE: 42-761EZ Chassis Restoration - Arran - 02-18-2013
I suspect that maybe there is a bad mica in the BC band oscillator circuit, either that or one of the trimmers/padders is shorting out or is full of crud. The trimmers/padders can be taken apart and cleaned, though it often isn't easy to get at them.
Regards
Arran
RE: 42-761EZ Chassis Restoration - Ron Ramirez - 02-19-2013
Another update:
Cleaned the band switch.
Now the 31M band is working.
It's too late in the evening to try the 25, 19 and 16M bands.
And, best of all - AM is working! Very weak - but it is bringing in some AM stations!
I'm frankly surprised AM works at all, as I measured the DC resistance of the AM oscillator coil primary and secondary prior to trying it out again. The primary is supposed to be 2.5 ohms - it measures just over 5 ohms. And the secondary, which is supposed to be 4.5 ohms, measures over 7.
???
I'll try it out again tomorrow as soon as I get home from work, while there is still enough daylight to receive something on the higher SW bands, and see what happens.
RE: 42-761EZ Chassis Restoration - Chuck Schwark - 02-19-2013
If I had to make two guesses as to the cause of those coil resistances going up, I'd say that the
greenies have corroded the wire in spots to almost nothing, in cross-section, but you still have continuity. Copper oxides mixed with the slight remaining copper causing higher resistance. and/or oxidized solder on the coil lugs to windings points??
Chuck
RE: 42-761EZ Chassis Restoration - Ron Ramirez - 02-20-2013
No evidence of green on the coil. Remember, Philco stopped using those nitrocelluloid insulator sheets on their coils once they switched to miniaturized coils at the beginning of the 1937 season.
Oxidized solder is a good call.
I'll look into that.I'm also wondering if moisture might be a culprit, and if I should remove the coil and bake it?
RE: 42-761EZ Chassis Restoration - Chuck Schwark - 02-20-2013
Ahhh..... notorious Di-hydrogen Oxide vapor....good call too.
Of course that sounds like a Royal PITA to get the coil(s) out.
#2
RE: 42-761EZ Chassis Restoration - Ron Ramirez - 02-20-2013
Actually, the AM oscillator coil is one of the few coils in the set that should be easy to remove. In addition to permeability tuning, this set has a conventional three-gang tuning condenser used on the first three bands, so the AM, SW1 and SW2 coils are not part of the permeability tuning assembly.
RE: 42-761EZ Chassis Restoration - codefox1 - 02-20-2013
I was just wondering if a floodlight aimed at the coils in question, but not so close as to harm other components could perform a satisfactory bake in situ. Thoughts?
RE: 42-761EZ Chassis Restoration - Ron Ramirez - 02-20-2013
Now, the latest:
I came home from work and went through the alignment procedure again.
AM is now working mostly quite well, but it's a bit wonky - if you tune from the low end of the band up, it starts making weird noises about 900 kc, as if it were breaking into oscillation. It does not do this when tuning from the top of the band down to the bottom.
31M still has an issue with the oscillator trimmer - 9.9 is coming in at 9.4, and if I try to adjust it to move the frequency up on the dial, it stops oscillating.
25M is dead - won't even respond to the signal generator.
19M, 16M and 13M aligned up well and seem to be working now. I picked up WWV at 15 mc on the 19M band just before 5 pm EST following the re-alignment.
Codefox, that isn't a bad idea. I don't have a floodlight, though - perhaps a hair dryer?
RE: 42-761EZ Chassis Restoration - codefox1 - 02-20-2013
Ron, you know those bulbs you have for outside illumination, like 150 watts or so. You can make a mask out of aluminum foil to focus most of heat on the coil while avoiding other areas.
A 100 watt regular tungsten bulb might work, or have I been asleep for a decade and these are no longer available?
RE: 42-761EZ Chassis Restoration - Ron Ramirez - 02-20-2013
Bill (Codefox) - I am quite aware of the floodlight blubs. I don't have any, and would rather not go out and buy a floodlamp bulb and something to put it in for a one-time use; I'd rather use a heat gun or hair dryer. Thanks for the thought, though.
RE: 42-761EZ Chassis Restoration - GarySP - 02-20-2013
Hi Ron. Just a thought from a newbie, but perhaps placing the entire chassis in the kitchen oven heated to about 150 degrees would work. I've done this with tuning condensers that were scrubbed in the dishwasher and it worked fine. Just dont get it too hot to melt any components.