42 1008 - Printable Version
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42 1008 - Bill Kinghorn - 03-01-2013
I just got a 42-1008 (Beam-of-Light) going and I need to be assured that it wasn't a waste of time. No time has been spent appearances yet. It required only new motor-mounts for the changer, new electrolytics, and two new paper caps to replace those with important levels of leakage. I was very careful not to disturb wires with hardened insulation. The rubber boots holding the needle have hardened and make record reproduction a bit thin. This radio has the only 78 rpm changer that I'd save from oblivion. The low-noise triode mixer with two IF amps is classy.
RE: 42 1008 - Arran - 03-01-2013
The paper caps ALL have levels of leakage, if you are using an ESR tester it is a waste of time to test 400-630 volt paper caps with it. Paper caps have a nasty habit of testing great with 9 volts across them but they quickly start leaking at 50, 100, or 250 volts.
Regards
Arran
RE: 42 1008 - Mr Grumpy - 03-02-2013
I just recently got my Beam of Light going in my 41-608. I'm going to experiment with a few other photo cells to see if they can improve the clarity of the sound as it is a bit tinny and garbled. I read that someone used RTV silicone sealant to replace the rubber bushings holding the needle bar, I tried it but had a hard time lining the bar up correctly while the sealant hardened. I also tried cutting thin strips from a latex glove and wrapped it several times around the bar and then crazy glued the last bit. This worked better than the sealant but I probably could have used more windings as the mirror jumped around a bit too much. I also fully cleaned and lubed the changer to make sure there was no drag on the needle bar.
I'm going to try and build a new needle and mirror assembly from scratch. I'll let you know how it turns out.
Please keep us posted as to your results, I'd love to know what works for you!
RE: 42 1008 - Bill Kinghorn - 03-02-2013
I was able to measure the leakage of all paper caps standing-off plate or screen voltages without disconnecting them. In all cases, there was a series resistor through which only the leakage current would flow, and across which the resulting voltage could be measured, with the set powered-up and maybe a tube pulled. I wasn't concerned with caps in low-voltage, low impedance circuits such as cathode bypass caps. After all, rolled caps with practically zero leakage probably didn't exist before polystyrene. The radio sounds MARVELOUS, much better than I thought possible with AM.
The idea for using, say silicone adhesive, to support the needle seems like a great one to me and I'm going to try it. I doubt that the needle needs to be centered exactly in the bracket and that only the mirror angle needs to be watched.
I doubt that the photo cell could cause bad sound quality though its sensitivity might be low. Remember that the line of light hitting it must straddle the edge of the window.
RE: 42 1008 - Raleigh - 03-03-2013
Antique paper caps are regarded as the most failure-prone radio parts other than electrolytics. They are prone to fail both suddenly and gradually, and when they short, they can burn out parts that are difficult to replace, such as IF and other coils.
Orthodox radio restoration advice since the '80s has been to replace all 'lytic and paper caps during a restoration, and with good reason. Not that modern caps can't fail, but they are far less likely to, since they are new and are of far improved technology.
My personal experience is that at least 75% of paper caps leak at rated voltage, which to me means their intact cousins will do so soon. I'd go ahead and replace them wholesale. By the time you've made the effort to test them, it's not that much more difficult to replace them all.
Unfortunately, replacing paper caps in those '38 to '42 Philco sets could disturb the brittle rubber wire insulation, requiring replacing or reinsulating that wire as well. But hey, it just adds to the fun and to the pride of completing a robust restoration to better than original standards of reliability.
RE: 42 1008 - Radioroslyn - 03-03-2013
Some run and hide from the '39 to'42 sets. Good observations John!
Terry
RE: 42 1008 - Bill Kinghorn - 03-05-2013
I had no trouble fixing the stylus in the bracket using silicone adhesive and now the phono sounds good. The adhesive is viscous enough to support the needle where it is placed until cured and placement isn't SO critical. The lamp adjustment allows for small departures from the original mirror angle.
I have replaced all paper caps where failure could damage other parts. There were only two. Others, where the level of leakage is unimportant, I've left in-place. Maybe after another 70 year they will leak too much.