Posts: 122
Threads: 22
Joined: Dec 2013
City: Meridian, ID
By way of brief introduction, I started vintage radio/TV restoration a couple of years ago. I have no background in electronics, but I've been able to pick up enough knowledge to keep me going through a few projects.
I picked up a very rusty, rodent-eaten Philco 645 this summer and I'm finally approaching completion of the electronic restoration. I got the full service info from Chuck Schwark, thank goodness.
My set is Run 3--stamped on the top of the chassis, and component changes consistent with Service Bulletin 234--except for two things, but I'm only going to ask about thing #1 at this time.
Bulletin 234: "Part No. 30-4114 (.06 mfd.) was added from the C- end of the B.C. resistor to the junction of resistor (66) and (67)."
That additional tubular cap was definitely not in the set when I opened it, but it has had service done. I want to put in that capacitor, but I don't know which of the three terminals on the BC resistor is the "C- end." (As I said--"no background in electronics")
Can someone tell me which is the C- end?
Thanks,
Winky
Posts: 7,212
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City: Roslyn Pa
Hi Winky and welcome to the Phorum.
The terminal you are looking for is the one that is next to the the ground lug on the BC resistor. It should have a wire connected to it and go to a 1 meg ohm resistor.
OR
IF you connect your volt meter - lead to the ground on the BC resistor. Measure the DC voltage either side of the ground lug. One side will have -10volts or so the other one will have +250 or so. The cap connects to the one with the - voltage.
GL
Terry
Posts: 122
Threads: 22
Joined: Dec 2013
City: Meridian, ID
Thanks, Terry. I'm looking for causes of some inconsistencies in Philco's voltage specs and my measurements. I placed the new capacitor, but it didn't change my voltage data. The voltages on the BC resistor, however, were -2.7 and -18v! Something's screwy, and I may have miswired one of the Bakelite dual condensers. I'll have to pull the condenser and chase some electrons to and fro. Again, thanks for your help.
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On your radio the BC resistor does not have any positive B+ voltage applied, so your voltage measurements are correct.
The -18 v terminal is the C- end and is where the capacitor should be connected.
Posts: 122
Threads: 22
Joined: Dec 2013
City: Meridian, ID
Thanks so much for clarifying that. I spent a few hours retracing the wiring and came up with one error--the 8 mfd and 12 mfd caps were reversed (not the polarity, just their positions in the circuit)--and switching those seems to have improved the audio and possibly the reception.
Posts: 7,212
Threads: 266
Joined: Dec 2009
City: Roslyn Pa
Hey Wink,
You should post some pics of it here! Some before and afters.
Nice work!
Terry
Posts: 122
Threads: 22
Joined: Dec 2013
City: Meridian, ID
I would declare that the electronic restoration is complete, but I still don't have anything on the shortwave band. I guess there some issue with the band switch, and I wouldn't even bother with it except that I have a couple of months before I can start working on the cabinet.
Nevertheless, the chassis is done and here are a couple of before/after photos. There's no attempt here to preserve antique value--I'm just trying to make it look close to the original.
[Image:
https://lh3.googleusercontent.com/-XeukV...520645.jpg]
[Image:
https://lh4.googleusercontent.com/-vfkfE...520645.jpg]
I think I understand the Shadow Meter despite my confusing post in another thread. The meter doesn't respond unless I use my indoor antenna (40 ft. of antenna wire on the ceiling). I originally thought the shadow would reduce to a thin line, but I don't think I'll ever create the conditions to get maximum response from the meter. This is a photo of the meter when a station is tuned accurately. The shadow is narrowed, but can't get any thinner because the vane doesn't return to the center. Some stations give a narrower shadow than this.
[Image:
https://lh5.googleusercontent.com/-5DFK3...520645.jpg]
If anyone gets really excited about Shadow Meters, here's a link to a 40-second video of the shadow and the vane movement during warm up and tuning.
https://picasaweb.google.com/coldrb/Febr...directlink
I'll post the cabinet when it's done. Thanks for everyone's help (here and on VideoKarma) in the successful restoration of another radio that I don't where I'm going to put it.
Phixing a Philco is like learning a phoreign language.
- Winky
