The PHILCO Phorum
Model 90 Cathedral stopped receiving - 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 90 Cathedral stopped receiving (/showthread.php?tid=21586)

Pages: 1 2 3

RE: Model 90 Cathedral stopped receiving - morzh - 08-29-2020

Scott.

Sorry, my bad: something happened and the browser showed me the other thread with your post #14.
Now it does not.

Never mind.

RE: Model 90 Cathedral stopped receiving - Eliot Ness - 08-29-2020

Quote:Need some help with the Volume POT here.  Pulled a lead off of it; it measures about 706Kohm Part# C.T.S. 5366-F  series # 40
On Ron's schematic it shows 500K (.5 Meg):

https://philcoradio.com/library/images/schem/90b.jpg

Not sure about the taper....

RE: Model 90 Cathedral stopped receiving - zboltman - 08-29-2020

Hi John,
Yes, I read about that 0.5meg thru your notes, (Thank You).
So, I opened up the pot, cleaned it, lubed it and re-measured it.
(Oh and by the way, the inside cover of the pot had a date stamp on it of Nov 6th, 1931!)
It is now measuring 2.8 meg ohm across the outer terms. 
From the center term, it does a clean linear measurement from side to side.
Yet, upon re-installing it; I still get noise when I adjust it.
(I put the old original tube in and it still didn't function, so I put the new, (24), replacement tube.)
The radio is still not receiving. 
I know I still have to do a lot of work to do about replacing individual components
I bought 2, a 24 and a 224 together.
The 24 lights up, but not the 224. :-(
Here are the notes from the seller:
One is a National Union NY-224 type 24A vacuum tube, and the other is a Philco type 24.
These tubes tested GOOD on a reliable Hickok Model 800A tube tester (a dynamic mutual conductance tester).     ... and NO shorts or gas detected.
They both had readings of 600 micromhos.  These tube are right at the minimum, but should still be usable. 
Ref:  Minimum readings should be 600 micromhos (60%) and new tubes should test at 1000 or more micromhos. 

Here is my question, based on the reference to the schematic, should I replace the original with a 500K ohm pot?

RE: Model 90 Cathedral stopped receiving - morzh - 08-29-2020

What did you use to clean the pot?
I found out, the pot is better left not cleaned but only lubed. Cleaning dissolves some conducting compound off the top.

RE: Model 90 Cathedral stopped receiving - radiohenry - 08-29-2020

Kinda hard to tell but it looks like the mica (all 4)on the tuning cap may have been damaged when blowing out the chassis. 
                                                            Henry

RE: Model 90 Cathedral stopped receiving - zboltman - 08-29-2020

I used a gentle plastic safe contact cleaner.
Guess its time to find a 500k pot...

RE: Model 90 Cathedral stopped receiving - morzh - 08-29-2020

Mark Oppat is the guy. He sells and fixes the tone/volume ctl pots.

RE: Model 90 Cathedral stopped receiving - zboltman - 08-29-2020

Hi Henry, I'm still learning my way around.
Could you please help me understand which one(s) you are talking about?

RE: Model 90 Cathedral stopped receiving - zboltman - 08-29-2020

Hi, I did a member search for Mark Oppat and could not locate him.
How might I get in contact with him?

RE: Model 90 Cathedral stopped receiving - morzh - 08-29-2020

https://www.oldradioparts.net/

RE: Model 90 Cathedral stopped receiving - radio1 - 08-29-2020

If someone has not already mentioned, drill out the candohm groundstrap rivet, sand down the chassis to metal, and the strap, then reattach with a new bolt, measure the section resistances to ground, this is can cause all kinds of symptoms. Measure the first RF plate to ground and see what you end up with.

RE: Model 90 Cathedral stopped receiving - morzh - 08-29-2020

I would wait with that. This does not happen often. It is sufficient to make sure the contact is good with an ohmmeter. When the radio is working, if there are symptoms, this could be addressed. Ground rivets do indeed sometimes show increased resistance but not in every radio.

RE: Model 90 Cathedral stopped receiving - Eliot Ness - 08-30-2020

Scott, sometimes the conductive layer of a pot just gets worn away and all that can be done is to replace it.  Some of the pots are wire-wound and not subjective to being worn away and respond better to cleaning.  For lubing a pot I like to use Deoxit Faderlube.

Quote:Hi Henry, I'm still learning my way around.  Could you please help me understand which one(s) you are talking about?
Henry is talking about the 4 areas I have circled, they have a thin mica sheet under the adjuster.  It's hard for me to tell if they were damaged but I don't think it would cause a lack of total reception if one or two were slightly damaged:

   


Quote:The 24 lights up, but not the 224. :-( Here are the notes from the seller:
One is a National Union NY-224 type 24A vacuum tube, and the other is a Philco type 24.
These tubes tested GOOD on a reliable Hickok Model 800A tube tester (a dynamic mutual conductance tester).    ... and NO shorts or gas detected.
They both had readings of 600 micromhos.  These tube are right at the minimum, but should still be usable.
Ref:  Minimum readings should be 600 micromhos (60%) and new tubes should test at 1000 or more micromhos.
I wouldn't make it a habit of buying tubes that tested that low.  Measure the filiment pins of that 224 tube and if it measures open I'd make the seller replace it.  If he balks at your request file a Not As Described claim with eBay.

RE: Model 90 Cathedral stopped receiving - Paul Philco322 - 08-30-2020

Plenty of sellers for good tubes, Findatube is one. 

Paul

RE: Model 90 Cathedral stopped receiving - morzh - 08-30-2020

Second what John said about the tubes.
Also.....if you know you are learning and have little experience, it makes sense for you to ask here before you buy a non-new part on eBay, rather than afterwards.
And as long as you are at it, if the buyer agrees the item is not as described, maybe he will agree to take both tubes back.