The PHILCO Phorum

My 71 I got a few months ago. Its a basket case. At some point it has been worked on and a lot of hacking went on. I have been working on it for about a week just trying to make heads or tails of what goes where.

I have found a couple schematics (Including yours Ron), and a parts list. I find it odd that there really isnt much in the way of parts lists and diagrams in the Rider books like most of the Philcos have. Was the 70 series kind a off the wall model or something?


Here is a few pics.









There is a lot of good to this radio also. The trans ohms out good, the OSC coil has continuity, on all legs but one winding which I'm not sure what it does as it appears not to be the osc but its not open it just reads about 11k hoping I can resolder the connections to fix that. Also most everything is here and I have a couple Mershon caps on the way.

I had the speaker reconed by Hank check it out:

Before:


After:


Sorry for the long post just wanted to vent.

Does this metal can cap look original or is it a replacment for a bad cap in one of the bakelite blocks?

It only has one wire coming out and it soldered to the leg of the 13k 3watt resistor thats on the cathode of the 36 tube. Also its not listed on the parts list or in the parts diagram.



Its installed here:


According to Philcorepairbench it is a .5mfd which could replace one of the .5's in the bakelite block 3615-AF (5 on the parts list).

I tried to attached the service bulletin for this radio but no go. Not sure what up with that.

Ahh I found the part. Its number 7 on the parts list. The part number wasn't very readable but after looking at it it is 3583.

Good that you are making progress. I've been reading your posts but haven't had a chance to dig out my 71 schematics and make an intelligent comment.

That reminds me, I still have to look inside the chassis of my 118B and find the shunt resistor for the shadowmeter so I can tell GlennPR where it is located. It isn't shown in the under-chassis diagram. Nice of Philco to occasionally leave out a detail or three here and there, eh?

By the way, the new cone on the speaker looks great. Two thumbs up to Hank Brazeal.

Looking good Keith!

Ron, speaking of the 118,I guess I should get some pictures posted.

Glenn

Another question for you fellas.

There is a cap thats connected to the ground side of the 2 10uf elec caps. It is a .05uf 630v it is once section of part 21 on the schematic. What is the purpose of this cap?

Ron Ramirez Wrote:Good that you are making progress. I've been reading your posts but haven't had a chance to dig out my 71 schematics and make an intelligent comment.

That reminds me, I still have to look inside the chassis of my 118B and find the shunt resistor for the shadowmeter so I can tell GlennPR where it is located. It isn't shown in the under-chassis diagram. Nice of Philco to occasionally leave out a detail or three here and there, eh?

By the way, the new cone on the speaker looks great. Two thumbs up to Hank Brazeal.

That's strange, it's shown on the under chassis diagram I have for a Canadian Philco 3118. It's basically a porcelain tube with wire wrapped around it mounted in a threaded rod roughly legthwise in the center of the chasis, the reason I know about it is that mine is open. Now if only I could find a 9'' Philco speaker for my 3118, I think it's a K7 type.
Regards
Arran

ipwizard Wrote:Another question for you fellas.

There is a cap thats connected to the ground side of the 2 10uf elec caps. It is a .05uf 630v it is once section of part 21 on the schematic. What is the purpose of this cap?

Suspect it was needed to suppress spurious oscillations in the audio stages.
Richard

That's correct. If you notice, there's no other bypass cap for the screen of the output tube. It ostensibly gets bypassed to 'ground' via the filter cap #56? . But since the negative of 56 doesn't go directly to ground this additional cap completes the circuit at audio frequencies.

Another question about this power section.



Does the two elec. caps and the two center taps pass through cap #21 on the way to ground? I think it does but I wired it such as all those connections tie directly to ground without first passing through #21 so I think I goofed.

Here is link to a pic of the schematic.

http://i1129.photobucket.com/albums/m501...ematic.jpg

Thanks

you mean the two caps labeled (40) ?

I see no reason to tie them trough (21)

It would not be drawn to GND if it was passing elsewhere...

The filter caps find DC ground via what looks like resistor #52. (up and to the right from the xfmr center tap) That puts their negative terminals several volts 'above' ground and that voltage is used for biasing.
What I mentioned before is the ground path for any residual audio/IF that may be on the B+ line. You'll note that there are no other bypass capacitors on the B+ line up to R24 - and then there is #5 for bypassing beyond that resistor. In theory #21 could be placed anywhere along the B+ line. But, as Richard said, that particular arrangement may have been best for preventing spurious oscillation.

Ok the light is starting to shine a little brighter now. I didn’t even think about the circuit finding ground through resister 52 but it makes sense.

I'm still learning about how these different circuits work and why there’s a cap here and a resistor there. This is a first radio I have worked on that has been butchered this bad where I've had to reconstruct parts of it.

I appreciate all of the help!

Finally got to the power up point yesterday. I brought it up on my variac with no tubes no issues, then popped in the 80 tube and brought it up to around 115vac in, no issues 80 plates had about 700v on them, 5v on the filiments and I didnt check for DC. So I shutdown and tried again with all the tubes then it happened. I smelled something getting hot and saw a couple wisps of smoke at around 100vac in. I shut down in a hurry and felt around and found a resistor in the power supply getting hot (~140 deg). It's the 10k .5w resistor (#54, arrow in pic below). Not sure whats up yet I had to stop playing in radio land after I found this hopefully tonight I can take another look at it. The resistor I am using for #54 is a 10k 2w.



Also can someone tell me if the circled part of the pic is connected or just crossing over each other? I have them connected which might be causing the problem?

I also changed the title to for the thread to something more fitting..

Yes that is a connection. If it wasn't the filament in the 80 tube wouldn't light. As for your resistor issue check for a short to ground at the point that the bakelite cap is connected to that resistor.
Terry