The PHILCO Phorum

First time poster. Recently decided to try and restore a radio I picked up a couple of years ago. Has been a nice bookcase antique.

I dabbled in ham radios back in my youth and grew up around people repairing tv's so I have a basic understanding of tubes, electronics, theory, and wiring. However it's been 30+ years since I tapped into the knowledge.

Did a good amount of research the past few days on this radio and the chassis. That led me to this site which has given me even more info on the effort needed. I have zero equipment to test any electrical components.

Without posting a bunch of pics, here is what I know:

Does turn on but there is a little play in the control/dial before it clicks on
Produces scratching sound when turning up the volume
Tubes are very faint after an hour of power. No color changes
Frequency dial seems good but no transmission locked in

I gently took out the 5 tubes (without removing the chassis) to look for indentifing marks as well as damage. Saw no physical damage (cracks) but I did notice that the 7B7 tube was a bit oxidized where it connects to the chassis. As well, 2 of the tubes are missing pins but I'm guessing that is by design.

What I need help on:
Getting the chassis out without damaging the housing to further look into things
Pointing me in the right direction for things read up on

If anyone is interested in this please let me know. I'm happy to post pics if I am in the right place.

John

Welcome to the Phorum!


Here's a link to a schematic for the PT-6  and a link where you can get one that is more readable: audiophool (you need the Djvu plug in available on his home page to view the images).

You will need to replace all the paper and electrolytic capacitors and check the resistors (some folks just replace all of them as well).   So if you don't have a digital multimeter you will need to get one as a bare minimum of test equipment.  The most recent one I bought was at Home Depot but there are many out there.  

I have not worked on a PT-6 so my advice on getting it out of the cabinet is only general but you need to remove the knobs, unscrew the chassis screws that are located under the cabinet, unscrew any screws on the back if yours still h as its back.  At that point I THINK it should just slide out the back of the chassis.  May need to wiggle it a bit to get it started and slowly pull it out.  Watch for things to hang up on the way out and go slowly.  You'll get it.

Read through some of the threads in this phorum including some of those in the Tech section.  A good beginner read that I like is on Phil Nelson's site: https://www.antiqueradio.org/begin.htm

Your 1941 set may have rubber insulated wiring that may be in need of replacing or sleeving...see: http://www.philcoradio.com/phorum/showth...?tid=14959


Read and ask questions here...lots of folks to help with your restoration!

Bob,

Thanks for your welcome and link to the more readable schematic

I was able to remove the chassis. 2 knobs and 2 screws. The power knob gave me fits, turns out's pretty gunked up. 

Here is a pic of the bottom. I was surprised at the lack of dust considering there's no back piece. I've never cleaned the inside.

[attachment=18147]

After reading Ron's thread on the rubber wiring, I decided to take a much closer look at all the wiring and, yeah, made my heart sink a bit. I'm surprised I didn't blow the thing up when I turned it on. Things touching things where they probably shouldn't be. Even more what I see is a lot of reddish buildup around all the solder points on the tube connections. As well, the soldering all over seems to be a bit heavy. 

I think this is going to be a bigger undertaking than I thought. No worries, I enjoy a good challenge. Replacing the caps might be short term to see if things are working. But I think that alone isn't going to be enough long term. Wiring and other things will need to be replaced as well. Why not just do it all at once?

Phil Nelson's beginner site was very informative. His knowledge of capacitor types for old radios was very insightful. You can see from the pics that there are a lot of old ones that are not very reliable and should just be replaced. I am looking into some more modern ones here: https://www.justradios.com

At this point I'm thinking of starting by replacing the capacitors and see if that gets the radio working properly. No point in re-wiring it without knowing what the root causes are? Would that make sense?

Some questions on the capacitors I am seeing:
The electrolytic one is rated mfd 20/20 on the schematic, but I don't see the voltage. The blue one in there now is VDC150. Without the schematic stating otherwise do I assume that is the correct voltage? I know that I can go higher in voltage, but I'm having a hard time finding one rated 20/20 at 150vdc.
Can the one in the middle that has the coil around it be replaced with a modern cap that doesn't have the coil? 

Given all that, I'm looking for some thoughts/comments on what I've observed and what I might have missed.

Thanks again for any help!

John

Yes you can just replace the cap that has the coil of wire around it with a regular modern film cap although its not too hard to keep the coil as well. If you are stuffing the existing caps (i.e. taking them out, heating them to soften the wax and pushing out the guts, putting the modern cap inside and adding back wax or hot glue to keep the original look) you can just rewrap the wire.

You can use two individual electrolytic caps in place of that multisection cap. It is a replacement anyway and a different, philco multisection cap was in there originally.

Just Radios is a good place to buy caps. Take your time, this is a good radio to start on; relatively simple and lots of room to get at the parts.

C5, the capacitor with the coil wrapped around it and connected in series with it is a chassis ground to AC line bypass.  They used a large value capacitor here which typically would have a lot of reactance.  The series coil is designed to resonate with the capacitor to bring the impedance down at frequencies of interest (usually the IF frequency).  Later in the history of the All-American Five design, the standard AC-DC five-tube radio, engineers went to 0.05 µF with no series coil.  If you replace it, it is your choice whether you retain the coil and it would probably be unnecessary but it would be cool to restuff it and retain the coil.

I have a box of yellow film caps here from justradios.com that I bought from Dave Cantelon directly at a London Vintage Radio Club meeting in London, Ontario and none of them have failed or drifted, so those are my choice for any recap job.