The PHILCO Phorum
A Philco 91 restore - Printable Version

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RE: A Philco 91 restore - Radioroslyn - 01-12-2017

If you want to fix your old switch, pre war National Co communications receivers used a similar set up for their off,on, the stby switch. It used two toggle switches one just past the other. When faced w/a bad switch I used a generic bat switch. Shortened the bat and cut a notch into the leaver for the pin to actuate it. Worked fine.
Would be a lot easier to replace your with a switch w/one from a 70 or so...

RE: A Philco 91 restore - klondike98 - 01-12-2017

Thanks Terry! In addition to the bat switches there are modern versions of the ball/lever switch I think would work as well. One example from Amazon at this LINK. So I have lots of options...no worries!

RE: A Philco 91 restore - Mondial - 01-12-2017

Bob, does the switch still work mechanically and snap normally between the two positions?  If it does it is usually possible to get it working.

Sometimes if the switch has been in the off position for many years, an insulating layer of oxides builds up on the contact surfaces. If you spray with contact cleaner and "exercise" it under load, many times it will come back to life.

RE: A Philco 91 restore - klondike98 - 01-12-2017

Thanks Mondial, I will give it some deoxit and try to revive it.  It does still work mechanically so there is a chance.

UPDATE: yes! the liberal application of deoxit to flush and clean got it working again. Took awhile to get the closed switch to show zero resistance but we got there... Icon_smile

RE: A Philco 91 restore - klondike98 - 11-13-2017

I've gotten back to this model 91 and am recapping.  Bakelite block cap#9 ( 6287-C ) is a 0.15uF with a 200 ohm resistor. (The resistor and capacitor are wired in parallel.) Here's a link to Ron's annotated schematic:
http://www.philcoradio.com/images/phorum/schem/91.jpg

So I got the resistor out and could use it but the lead is very fragile (I think I lost some of the wire strands in the process of removal) and its probably better to replace it. I'm not sure what wattage would be used, but it looks like a wirewound resistor. Does anyone know if a 2 watt 220 ohm resistor would work OK in the circuit? Thanks!

RE: A Philco 91 restore - Steve Davis - 11-13-2017

I would just trim the ends and reinstall the loop.

Steve

RE: A Philco 91 restore - Radioroslyn - 11-13-2017

> Does anyone know if a 2 watt 220 ohm resistor would work OK in the circuit? Thanks! 
Did a quick calculation and 2w is plenty, came up w/abt .25w.

RE: A Philco 91 restore - klondike98 - 11-13-2017

Thx guys.
update:  I looked at the resistor package that was embedded in the bakelite block and was able to unwrap it.  Here's a pic of the insides.  Just a resistance wire bundled into the paper package.  As Steve suggested, I was able to easily trim and strip off the insulation on the ends, repack it and wire it back in place...easy peazy.

[Image: https://www.dropbox.com/s/zkwe4leaoudlrhl/philco91_11.jpg?raw=1]

RE: A Philco 91 restore - klondike98 - 11-16-2017

Good progress over the last few days.  All recapped and several of the dogbones replaced.  I did add an inline 1.5 amp fuse to the hot side of the line and repro power cord and polarized plug.  Here's the underside ready to go.

[Image: https://www.dropbox.com/s/7d91bl84f4wkoxm/philco91_12.jpg?raw=1]

I put the tubes back in and powered it up.  The filaments all came on except I could not see anything in the 80 tube.  No sound at all in the speaker.  Did I forget to check the power tranny before I started?  Secondary across the two 80 plates looked ok as did the secondary on the 80 filaments.  Checking the primary at the power plug blades I was getting fluctuating readings ranging from .5 meg on down to a few k so I unsoldered one of the primary leads to the on-off switch and measured the primary directly.  Looks ok at a few ohms so the problem has to be in the on-off switch or my solder joint....it was my solder joint.  Resoldered the tranny lead and fired it back up to the sounds of my SSTRAN station.  The shadow tuning even works although I think I can adjust it to be a bit brighter.  Can't believe it but there is still one of Philco's special straight filament light bulbs on the shadow graph.  

[Image: https://www.dropbox.com/s/ly1bdd52ereyye3/philco91_13.jpg?raw=1]

I still need to do some chassis cleanup, the tuning cap is pretty dirty and the dial scale needs to be replaced.  The volume control pot was a bit scratchy.  I'll also check alignment but it seems to be pretty good.  The tube shield has some surface rust I need to take care of but I'm happy its playing with no major problems.  The cabinet work is under way but that's another story...

RE: A Philco 91 restore - klondike98 - 11-09-2018

I thought I was all done with the 91B but when I went to check it out to get ready to reinstall it into the cabinet the tuner was not rotating all the way. A quick look and I could see the dial cord was fraying and causing the problem. This set uses a thick braided dial cord, something on the order of .06 inches or 1.7mm. Just for grins I tried using the 0.028 cord that is sold by various folks but it slipped on the dial pulley. I tried a double loop around the pulley...no go. So have ordered some 1.7 mm braided cord that was discussed in one of Ron's posts for a 16 dial cord.
.

RE: A Philco 91 restore - klondike98 - 11-11-2018

Dial stringing was successful.  Its a bit of a bear to get the cord around the tuning knob pulley but the use of a dental tool with a hook on the end made it doable.  A crochet needle would work as well.  I was lucky enough that the cord was still in place although frayed so I could map it before taking it out.  I did look around quickly for a string diagram and did not locate one so here's one from my notes:

[Image: https://www.dropbox.com/s/f3twh9rotgk4g2r/Philco91B_dial%20string.jpg?raw=1]

RE: A Philco 91 restore - Ron Ramirez - 11-12-2018

It's covered in the Tech Section of the Phorum:

http://www.philcoradio.com/phorum/showthread.php?tid=14971
https://philcoradio.com/library/index.php/shop-talk/techniques/dial-cord-stringing-diagram-models-14-17-18-43-71-91-118-others/

Icon_biggrin

Nathan had found a better type of cord within the past year or so. The source (Amazon) is mentioned in the link above.

RE: A Philco 91 restore - klondike98 - 11-12-2018

Big eye roll... Icon_redface
Somehow I missed that.... thanks Ron!