The PHILCO Phorum
Model 90B Tinkerer - Printable Version

+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: Model 90B Tinkerer (/showthread.php?tid=23006)

Pages: 1 2 3 4

Model 90B Tinkerer - Simon Wa3uay - 11-17-2021

I've been following Bob Andersons trials and tribulations on his 90, but this one in pretty good shape overall.  Like his, this has a single 47 output tube.

What's missing:
-the Large tube shield (with tube layout sticker)
-another shield on the other side (there's a clip there)
-one of the original filter capacitors
-no stickers!

Other:
-strange shape of the volume control shaft, makes the knob wobble. Don't want no wobbling knobs!
-strange red grounding wire on the choke housing to the chassis
-deformed tuning dial

Tubes all test good (2 may be original). I use an old Signal Corps I-177 tester.
The tubes all light up with the rectifier removed.

Transformers, including PT, speaker, output transformer, and choke all seem to be good except for the RF 1st Det. coil (7), open primary.  What a surprise.

BTW, I've found that a dab of WD-40 on the grid caps and tube pin sockets make them suckers jump right out of there! I use a q-tip. Also grip tubes by the base, not the envelope.
And, now for your viewing pleasure:
   
   
   
Notice the shape of the volume control shaft
   
   
Big red ugly wire grounding the case which is insulated from the chassis (?!)
   
All that green stuff is fragmented wire.
   
91 turns required (don't laugh at my winder! it works)  That's 3m electrical tape sticky side out, one layer.
   
That's all folks (until round 2)

RE: Model 90B Tinkerer - Bob Andersen - 11-17-2021

Regarding the filter choke. It looks like there are phenolic insulating washers on the mounting screws. Mine is metal on metal. I'm thinking they might have been trying to reduce hum by making a single, solid grounding point ?

Also I suspect that is a replacement volume control. You could try building it up with some solder or JB Weld.

RE: Model 90B Tinkerer - Simon Wa3uay - 11-18-2021

Thanks Bob- i will try to solder a shim on the shaft- and remove the ugly red thing and put choke back like its supposed to be.
I'm thinking of putting the tubes back in before I replace caps and resistors to see if it's alive. I would bring it up slowly and monitor AC voltage and current, as well as B+. There's a spider web of replacement capacitors and lifted resistors floating in mid-air.
Or is that not a good idea?
-Simon

RE: Model 90B Tinkerer - Bob Andersen - 11-18-2021

I suggest you did what I did with mine.

1. Disconnect or replace the AC line filter caps. They are in circuit even with the radio turned off and have a nasty habit of popping.

2. Put all the tubes in except the 80 rectifier and power it up. No need to do it slowly, just go for 117 VAC. All the tubes and dial lamp should light up. You can check the power transformer secondary by stick your AC voltmeter probes into the 80 tube socket. 5 volts across the fat pins. Something like 500-700 across the smaller pins.

3. Replace the two electrolytic caps and apply full power using a dim bulb or similar current limiting device.

I don't really see the point of slowly powering it up unless you're trying to reform the old electrolytics.

RE: Model 90B Tinkerer - Simon Wa3uay - 11-19-2021

Already did the no-rect-tube-PT-voltage-check, all ok. Didn't think about AC line filter caps, anyway they didn't 'pop'.
OK on the electrolytics, I will check them out next, then see if it's alive-
Thanks Icon_smile
Simon

RE: Model 90B Tinkerer - radiorich - 11-20-2021

Hello Simon,
Well I may have a Volume control in my stash of Controls but I will not be able to check that stash till winter break .
Sincerely Richard

RE: Model 90B Tinkerer - Simon Wa3uay - 11-20-2021

Thank you Richard, that is good of you.

RE: Model 90B Tinkerer - Simon Wa3uay - 11-24-2021

It's looking like the 3,500 ohm segment of the large tubular power resistor is bad. It's measuring 70K building up to 90K with a digital VOM. I tried resoldering the ends, but that stuff they use is flimsy cloth covered stuff and just came apart.
Question is, what watt 3.5K resistor will work?
-Simon

RE: Model 90B Tinkerer - morzh - 11-24-2021

Simon

What section on the sch is the 3500 Ohms?

RE: Model 90B Tinkerer - Simon Wa3uay - 11-25-2021

Bottom right 58 between 3 and 4 Mike

RE: Model 90B Tinkerer - cknob - 11-25-2021

Hi Simon...I'm new to the forum and vintage radio restoration in general. Having a problem with the same resistor...only 1750 ohms from end to end. 200 ohms from terminal 1 to 2...1750 from 1 to 3 and 1750 end to end. Resistor starts to burn up at terminal one on power up. Popped the electrolytic connected to it last night.

RE: Model 90B Tinkerer - Simon Wa3uay - 11-25-2021

Hi cnob, I was tempted to fire this thing up but now glad I didn't. I'm going to trace out all the circuits first because the wiring is a mess. BTW, the 2 filter capacitors 56 and 57 should be 6 uf

RE: Model 90B Tinkerer - cknob - 11-25-2021

Gotcha! Thanks so much

RE: Model 90B Tinkerer - Simon Wa3uay - 11-27-2021

Update on the Tubular Resister 58 - now it's working!
I unsoldered the lead going to F.C. socket (terminal 4) to isolate that part of the resistor, and must have reflowed the solder, because it then measured about 3.6K. Soldered back the lead and measured 3.4K or so. I think condenser 24 is having some weird effect on it.
-Simon

RE: Model 90B Tinkerer - morzh - 11-27-2021

SImon


I am not sure, but I think it dissipates 5.7W. So you need 10W rated resistor to sub it.