Model 90 Cathedral stopped receiving - Printable Version
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Model 90 Cathedral stopped receiving - zboltman - 08-27-2020
I acquired a Philco 90 Cathedral.
With all your help I have progressed nicely, but have now taken 2 steps back...
The unit received stations when I got it. Now it does not.
It has always had a problem with the volume control. Very scratchy and intermittent.
(Should I replaced this? Can an original be located? Can I used a modern pot?)
Since, then, this is what I have done:
Changed power cord.
Added metal shield
Cleaned all the bugs and crap out and off of it.
(I blew it off and used contact cleaner.)
Replaced the type 24 tube. (Det-Osc)
(The tube did not light up anymore.)
(The one under the 3 tube shield.)
Changed the Pilot light. (used an E10 6.3 volt)
Gee, here I thought I was doing great things for it, and now it is mad at me.
Maybe all the dirt was holding it together?
Anyway, any suggestions on where to start troubleshooting would be very appreciated.
RE: Model 90 Cathedral stopped receiving - morzh - 08-27-2020
Do you still have audio?
Can you pass RF signal through it and get the tone?
RE: Model 90 Cathedral stopped receiving - radiodale - 08-27-2020
Have you changed the electrolytic caps?
RE: Model 90 Cathedral stopped receiving - morzh - 08-27-2020
They look like they have been changed.
RE: Model 90 Cathedral stopped receiving - zboltman - 08-28-2020
The speaker humms and makes the scratchy sound when adjusting the volume.
I will need to learn how to put RF into this.
RE: Model 90 Cathedral stopped receiving - zboltman - 08-28-2020
That sounds like a great idea.
My question is this:
Is it OK to put new style caps into a restoration project?
Do I need to find old replicas?
RE: Model 90 Cathedral stopped receiving - morzh - 08-28-2020
It is OK to put any part that meets the electrical specs.
It is up to you if you want to make the replica parts (restuff caps, overmold resistors) or buy them, it is not required for the radio to work,
RE: Model 90 Cathedral stopped receiving - zboltman - 08-28-2020
If you are referring to the shiny caps, they are not replaced; I just polished the tops...
RE: Model 90 Cathedral stopped receiving - Eliot Ness - 08-28-2020
Quote:If you are referring to the shiny caps, they are not replaced; I just polished the tops...No, Mike (morzh) is referring to the two electrolytic capacitors circled in red below:
They are obviously not the original capacitors so they were replaced at some time.
As far as your radio not receiving it could be as simple as a bad tube or some other component. The most commonly replaced items in these old radios are capacitors, resistors, and tubes.
First make sure no wires came loose when you cleaned the chassis... take a slow long look with a strong light (emphasis on long and slow) looking for anything amiss. Also, just for kicks put that old 24 tube back in and see what happens. Sometimes it's hard to see the filaments glow and it is possible you swapped out a good tube with a dud.
Then report back with a picture of the bottom of the chassis if you don't mind. As far as the volume being scratchy you might be able to clear that up with a squirt of WD-40 into the pot if you can find any openings.
One more thing, are thopse screw tops on the two capacitors I circled in red? If so unscrew them and take a good picture for us...thanks!
RE: Model 90 Cathedral stopped receiving - morzh - 08-28-2020
What John said.
And...those you polished are not caps by any stretch. Those are RF coils.
RE: Model 90 Cathedral stopped receiving - zboltman - 08-28-2020
Here are pics of the capacitors and underneath.
RE: Model 90 Cathedral stopped receiving - morzh - 08-28-2020
The capacitors were replaced at some point, judging by the inside caps - in 40-s or maybe 50s.
They need to come out and be replaced by new ones.
As long as you are at it - they seemed to have not cleaned the insides well: the perforates polastic sheet has to be either removed or washed very well.
I also recommend soaking the cylinders in vinegar, it will take care of the green stuff.
Then re-assemble with the new caps.
RE: Model 90 Cathedral stopped receiving - Eliot Ness - 08-29-2020
Scott, Mike is correct, those capacitors in the cans are (older) replacement electrolytic capacitors and should be replaced at some point if you plan to play the radio very often, but it would be nice if we could get the radio working again before you start replacing a lot of parts. Below I have labeled some of the parts underneath the chassis and will explain what those components are:
Your radio looks like it is an older restoration, but most of the capacitors they used are due for replacement. I have some of those that are NOS and even unused they measure a high level of leakage.
1: These are Bakelite blocks that contain paper capacitors, I have only labeled one, but you can see there are many.
2: These are (older) replacement paper capacitors that that were used to replace the capacitors in the Bakelite blocks. Instead of putting them inside the blocks they just soldered them on top of the blocks. I can't tell from the pictures, but the problem with doing that is if you don't disconnect the old blocks that old capacitance will effect the new capacitors. At any rate, at some point in time, all the capacitors in the blocks and those jumpered on top will need to be replaced.
3. This is a large wire wound resistor with several taps on it (part# 58 on the schematic). Yours looks to be in nice shape but an open in one of the sections could kill the radio.
4. These are resistors, we call them dog bone resistors today. I didn't label them all but enough so you should be able to ID the rest. These typically creep higher in value and if 10 or 20% higher than marked should eventually be replaced.
The easiest fix is a bad tube or maybe one that isn't seated well in its socket. Pulling them out one at a time, cleaning the pins with scotchbrite and reseating is not a bad idea. Have you tried putting the old #24 back in the radio yet? If you have access to a tube tester it would be a good idea to test them.
EDIT: If you need schematics and part lists PM me your email address and I'll send you some hi-res copies.
Edit2: Rather than regurgitate what has already been covered here are some links you might find helpful:
The first is a restoration of a model 90:
https://mcclellans.com/Philco90Restoration.htm
Another restoration thread by Steve Davis. Although this is a push-pull 47 chassis you'll find many similarities:
https://philcoradio.com/phorum/showthread.php?tid=20685
From the Philco library this tells you what is inside each of those Bakelite blocks:
https://web.archive.org/web/20170227100418/http://www.philcorepairbench.com/bblokcap.htm
And here Mike (morzh) describes the no-mess method of re-stuffing those Bakelite blocks with fresh capacitors:
https://philcoradio.com/library/index.php/shop-talk/techniques/bakelite-capacitor-rebuild-without-desoldering/
RE: Model 90 Cathedral stopped receiving - zboltman - 08-29-2020
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
OK, I looked thru the Riders manuals and any schematics I could find and no where does it give the specs for this pot.
Please help me to verify the resistance of this .
Also, could you folks tell me if it is linear taper or audio taper?
I also searched all the documents and resources at philcoradio.com and did not find part # 5366
RE: Model 90 Cathedral stopped receiving - zboltman - 08-29-2020
I'm sorry Mike, I am still learning.
Really thought I was only posting in this Electronic Restoration thread.
Could not locate the other one you are mentioning.