[klondike98]

Am working on a 49-905 that I picked up.  It has a multicap electrolytic can with 40-40-70 uF.  Got the can apart to stuff new caps inside.  The can shell itself is the common negative that is at B-.   Just to be sure I hadn't caused a problem I checked for shorts between the 3 lugs that connect to the positive side of each of the 3 caps and the can shell.  I find that there is a measurable resistance between each lug and the can that ranges from 1 to 2 meg ohm.  There is a red colored rubber-like coating at the base of the can where the lugs connected with the guts of the can.  I cleaned the rubber, sides of can, and wafer around the lugs with alcohol but still see measurable resistance.  I put the ohm meter probes on the rubber itself and can measure resistance across the rubber.  I suspect it has gotten impregnated with the old electrolyte.  I might be able to dig out the rubber but its fixed in there pretty well.  
Has anyone seen this before and have a fix?
I assume this leakage between B- and the positive leads is not acceptable; correct?
Pic below showing the rubber coating on the inside of the can bottom. Thanks for the advice in advance; I suspect there will be more questions as this project proceeds.

[Image: https://www.dropbox.com/s/jydsn1ty00s7qm....jpg?raw=1]

[morzh]

I never bothered too much about it. However I don't think you need to keep those lugs in the firts place. You won't be able to make the case the common nebgative again so you will have to drill another hole and thread the common negative wire through it. In the same fashion you can drill out the lugs and thread three wires through and then connect them to the caps' leads. Then you could care less about the resistance.

If you still want the lugs used, just moat each lug instead of trying to clean the whole thing.

[klondike98]

Thanks Morzh, I do want to keep the lugs since they are used to connect to a number of other components and this is a very small tightly packed chassis so I'll try to moat them as you suggest.

[morzh]

What are you gonna do about the common?

[klondike98]

The can actually has three additional lugs that come through the bottom of the mounting wafer which can be soldered and are used as a B- connection for several other components in the set.  Those 3 B- can lugs are twisted slightly so I suspect they are what holds the can shell to the mounting wafer.  So I'll drill an additional hole through the base and connect the common negative to one of those lugs.  The can will be at B- and the three positive leads will come through drilled holes next to each of the positive lugs.  I just need to moat the lug bases that touch the rubber and insulate the positive leads that go through the rubber and wafer base to ensure they don't short or leak current to B-.  The can has a cardboard sleeve that fits over it for insulation from idle fingers and I will probably just slip that over the base to cover the three new caps.  
You can see 2 of the 3 B- can lugs in the photo below.  I also labeled the 3 lugs for the positive end of the caps though you can only see 2 of them.
[Image: https://www.dropbox.com/s/epg21qujuqdph8....jpg?raw=1]
[Image: https://www.dropbox.com/s/jjr76cas3rqpsv....jpg?raw=1]

You'll see that this multicap can is actually an old repair since it is only a 40-40-40.  There was an additional 30uF cap tacked in place under the chassis to bring the cap up to 70uF.
[Image: https://www.dropbox.com/s/k3hibqt5hgyygb....jpg?raw=1]

This is an AM/FM set and is pretty well packed into the small chassis.  Its going to keep me out of trouble for awhile!

[klondike98]

Question #2 - On the back of my 49-905 the label that relates to the antenna lug is missing.  I found a picture on-line that is not really readable but seems to indicate that if you want to use an external antenna you remove the blue wire lug from the screw and do something.  IF you want to use an FM dipole antenna you....???  Does anyone have a 49-905 with this label and if so would you transcribe what the label says for me.  Thanks in advance!!
[Image: https://www.dropbox.com/s/u2we2q6oguq66u....jpg?raw=1]

[klondike98]

On the tuning cap there is a wire connected to one of the lugs on the top but is not connected to anything at the other end.  Was this some type of gimmick to improve reception like Ron referred to in http://philcoradio.com/phorum/showthread...8#pid47468 ?  I can't figure it out from the schematic ( http://www.nostalgiaair.org/Resources/674/M0013674.htm ).  Here's a pic of the wire in question -- it curls in a few loops within the yellow oval and is attached at the yellow arrow) .  Advice on what to do with this wire??  

[Image: https://www.dropbox.com/s/4bwmxmcx5duzag....jpg?raw=1]

[klondike98]

I started this thread a long time ago, it was only my 4th radio restoration. The 49-905 turned out to be missing the broadcast loop antenna. In this set it was one of those that was glued around the inside of the case near the back. At the time I had the FM working OK and for that reason the set became my shop radio. I also had a soft spot for 1949 as its my birth year. I've toyed with trying to fabricate a loop for the set but never got around to it until recently. Just to see if I could make something that would actually pull in stations I put about 20 loops of 30 gauge wire around a cardboard box frame and wired it in. Lo and behold it worked just fine, not there is that much to listen to on AM these days. I may try to make something that's a bit more permanent and closer to the orginal look but for now it will do just fine.

   

[morzh]

Bob,

These loops are tuned ciruits with the tuning cap, so the number of tirns should be same as originally.
So, after you made that antenna, do you have your dial in agreement with the input frequency if you try to align it?

[klondike98]

Thanks Mike. So far I was just happy to get clear reception. I’ll have to check the frequency tracking.