41-250 restoration - Printable Version
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41-250 restoration - keith49vj3 - 10-12-2017
All, I've been working on a basket case 41-250. The cabinet was a mess but I've finished the cabinet and now I'm working on the chassis. Nearly all of the wiring had to be replaced and what didn't deteriorate on its own was eaten by mice. Did Philco ever publish charts showing the tube voltages and resistance readings for all the tube pins? Given all the rewiring it would be easy to make a wiring mistake. If such a chart exists could someone help me locate one? I've powered it up and the amp is working but the oscillator is dead. I haven't installed the push button tuning coils yet since the mice chewed off all of the braided wire connections. I think the radio should play without the portion shown below in red, can someone confirm that for me? The audio transformer was open but a friend of mine happened to have the exact one in his junk box.
Thanks in advance,
Keith
RE: 41-250 restoration - morzh - 10-12-2017
Yes I think it should play without the pushbutton assy when the switch is in proper positions.
RE: 41-250 restoration - keith49vj3 - 10-13-2017
What would be the expected voltage on the grid of the oscillator tube. I'm getting a -1.8 volts, is that too low?
Thanks,
Keith
RE: 41-250 restoration - Radioroslyn - 10-13-2017
Think you are ok w/-1.8vdc. When it's 0 or + that indicates an issue. Can you read the frequency w/ a counter or hear it in a receiver?
RE: 41-250 restoration - keith49vj3 - 10-14-2017
I hooked up my scope to the oscillator grid. When I move the tuning capacitor in broadcast mode the amplitude changes greatly and the frequency varies from 1.8-2.2 MHZ. When I hook up my signal generator to the osc. grid I can get the radio to play and pick up all kinds of stations. In the shortwave position frequency does change when I move the tuning gang. I feel like I'm slowly making progress. Can anyone direct me to some decent alignment instructions? I can't read the ones posted on Nostalgia aire.
Keith
RE: 41-250 restoration - David - 10-14-2017
Looking at Beitmans from 1941 will display both the 41-250 and 41-256 both look very much alike the aligement steps are given only for the 41-256. Beitmans would do stuff like this to reduce the cost of printing. Hope this is useful info. David
RE: 41-250 restoration - Radioroslyn - 10-14-2017
Don't know if I would try to assess the osc frequency by using a scope to the control grid of the osc tube. The grid is a very sensitive to any outside influences by connecting to the grid you may be loading the circuit w/ resistance or capacitance from the scope, would cause some frequency shift or in some cases cause the osc not to operate.
Looking at it from the cathode of the mixer tube would be a better choice that's where the osc output is fed into the mixer.
As a practical matter when the set is set to receive the BCB the osc should be at 1005kc when the dial is set at 550kc and at 1955kc when the dial is at 1500kc. I try to keep it simple a 9v battery, $10 counter, and a small coil of wire. The 41-300 is tuned to KYW in Phily at 1060kc.
RE: 41-250 restoration - keith49vj3 - 10-14-2017
David, thanks for posting the alignment instructions.
Terry, You've wrapped a wire around your osc. tube and simply hooked it up to your counter? I'll give that a try using the counter on my scope. What's the failure rate on the large two section silver mica cap shown in the picture below? Yes, I still have more wires to replace.
Keith
RE: 41-250 restoration - Radioroslyn - 10-14-2017
>You've wrapped a wire around your osc. tube and simply hooked it up to your counter?
Correct.
> What's the failure rate on the large two section silver mica cap shown in the picture below?
Don't know. Haven't worked on enough of 40-42 models I try to stay away from them unless it's some thing special.
RE: 41-250 restoration - keith49vj3 - 10-15-2017
This radio had major mouse damage that had to be corrected. After removing the nest I discovered that all of the wires connecting the push button tuning coils were eaten. This was a bit surprising since the wires were woven un-insulated steel. All of the other insulated wires were damaged but not by the mice. It an attempt to figure out why my oscillator wasn't working I carefully inspected with a magnifying glass every wire and wiring connection that I replaced while double checking the schematic to make sure i didn't make a mistake. When i did this I found a tiny piece of the braided wire connecting to trimmer cap 17. It turns out that this entire wire was eaten and originally it connected to terminal 6 of the oscillator coil at a location that's hidden on the backside of the oscillator coil. After replacing this wire the radio works fine. What's the rational behind using braided un-insulated wire? I'll replace these with silicone covered stranded wire. Now that I know I have a keeper I'll finish replacing the rest of the original rubber wires. I'll post pics when I'm finished.
Keith
RE: 41-250 restoration - keith49vj3 - 11-03-2017
The generic alignment instructions were a bit confusing because they reference trimmers that are numbered differently on the shown model. Since the trimmer functions are labeled in the parts listing I added their positions as an aid to future 41-250 restorers below.
I made a new dial light difuser using Avery brand plastic file folder material.
And finally here are a few photos of the restoration. If it wasn't for the rubber wire this would have been an easy restoration.
More photos to follow
Keith
RE: 41-250 restoration - keith49vj3 - 11-03-2017
And finally here is the finished radio.
Keith
RE: 41-250 restoration - morzh - 11-03-2017
Keith
You really brought it back from "mostly dead".
Great job.
RE: 41-250 restoration - klondike98 - 11-03-2017
Very Nice!!!
RE: 41-250 restoration - KCMike - 11-03-2017
Beautiful job Keith.