[bfrohwein]

Happy Monday!

I picked up a 39-7 a couple of months ago. decided to start work on the chassis yesterday.

bad news.. it was a mouse-buffet at some point. ate the paper off one of the paper caps! good news is that I managed to get the antenna coil back together (no broken wires, lucky me) bad news is, the bugger ate a hunk out of the primary on the 2nd I.F. (#11 on the schematic)

since this set's IF is 470, I'm wondering if I there's enough adjustment in the padder to use a 455 coil?

I do have a 470 2nd IF donor, but.... it's 2 5/8" long and would span more than half the chassis underneath and cause me to re route wiring and possibly have the center terminal strip in the way. also, it ohms out kinda low on the secondary 1.2 ohms. the primary is @ 19.8.

not sure if this is truly an option or not, but I'm considering the source, Norm Leal. he wrote:

"With IF Transformers use small capacitors
between the plate of the driving tube to the grid of the
driven tube. This will allow the peaking of the one side of
the transformer which is still working. In this case, capacitor
values around 200 pf will usually work."

the last option was an article he wrote on the CHRS website.

Thoughts?


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[bfrohwein]

Never mind... I was able to remove the chewed off bits. soldered it back on the pins and I'm measuring 20.4 ohms now.. weird too, I removed a good amount of wire. I guess there's a mile on there!

now I just need to figure out why the other end of the primary was connected to no where.

[bfrohwein]

Have I ever mentioned how much I love rubber wire?

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[Eliot Ness]

Have I ever mentioned how much I love rubber wire?

Yeah, there's nothing quite like the feeling you get when you gently try to move a wire and the insulation crumbles. And it wasn't just Philco that used the bad wire, I've had Atwater Kent and Zenith sets that were also guilty of switching over to the rubber crumblies. I'm sure it seemed like a good idea at the time, but 70 years later we know the rest of the story.

[bfrohwein]

I'm always amazed that there's usually a couple of wires that defy age and stay pliable.

[morzh]

If the transformer did not burn, create stubs out of these wires and solder to them and then insulate the joint with some heatshrink.

[Nick3092]

My 39-6 (which is the same minus the push buttons) was the same. I just let it crumble off the transformer wires and put colored heat shrink over it. Worked well.

[Arran]

Rogers built sets used to use a lot of rubber (or gutta percha) insulated wire as well, going back to the early 1930s, they did not use it on the leads of the power transformers at all, nor much on the coils or IF transformers. My observation though, from working on a Rogers Ten-60, was that the white and yellow coloured stuff held up the best, the green and blue held up the worst, and the red and black was somewhere inbetween. Rogers had a connection to Grigsby Grunow in Chicago, who was also infamous for using rotting rubber wire.
Canadian G.E and RCA sets also used a certain amount of rubber wire, but they also used the cloth covered, I'm not sure why they mixed the two. It's weird stuff, some gets hard and crumbly, and turns to dust when you look at it the wrong way, but in other cases it gets gummy and dissolves off the wire.
Regards
Arran

[bfrohwein]

Already done...

I did an oops on the length of shrink tubing on one of the white wires and I ended up using brown over the black wire because well.. I'm out.

side note: has anyone ever thinned liquid tape? my black is so thick and chunky. noted the main ingredient is naptha, a shot of ronsonol?

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[David]

Liquid tape 20 or more years ago was nothing more than rubber cement plus something to make it black never trusted the stuff have no idea about todays liguid tape. Lots of parts in common with 38-12, 38-15 code 121 if you need to hunt for parts. Hope this helps. David

[bfrohwein]

turns out it's just cheaper to replace the bottle.. Ronsonol isn't pure naptha anymore.

I don't use it very often, but I do on these where the wire bends into into the coil, just in case. the PS works just fine.


the only thing I need, really, is the switch assembly. two of the switches are completely jammed up in the on position. whomever tried to fix it back whenever that happened mis-wired a number of connections and left a few disconnected. one of the 2nd IF primary wires was cut completely. I kinda don't think it worked after whomever worked on it.

I'm going to throw caution to the wind and see the switch assembly from a 40-125 works. all the mounting screws line up. I figure, what the heck, doesn't hurt to try.

[Ron Ramirez]

Looking at the two schematics, yes, it appears that you can use a 40-125 pushbutton assembly in a 39-7. They have different part numbers but the schematic drawings of each look the same.

[bfrohwein]

finally got the 7 pin socket and just put it in.. I have to rewire the 1st IF and I'm ready to fire it up.

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this one was just plastic.. and melts easily with the touch of a soldering iron tip

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