There Has to Be a Better Way.

[Winky Dink]

Here's my Philco 645 after doing all of the essential rebuilding and replacing.



Between disassembling components and removing everything on top of the chassis pan, it needs almost total rewiring. I started rewiring a couple of days ago, but every time I move to a new component or circuit, then something I did before looks wrong. Then I spend an hour confirming that my wiring was actually correct (or is it?).

Is there a systematic way to do this project without spending most of my time running in circles?

[marty59]

Quote: "Is there a systematic way to do this project without spending most of my time running in circles?"

No, not really!

I re-wired a Philco 40-115 (and others) and I look at all the crumbling wiring as a roadmap. I basically started at one end of the chassis and worked my way across. I followed along by terminal to terminal. Do the filament wiring, the B+ and notice how it flows. You can't just do it by circuit to circuit as there are too many interconnects. Make drawings/notes as you go along and confirm things with the schematic before and after.

Simple but time consuming and figure in a stopping point so you can continue fresh the next day.

[Kamakiri]

Agreed. Just be thankful that you're not doing a 37-650. There are caps in that thing that I swear were installed before the chassis metal bending was finished. Between rotted rubber wiring and bakelite block condensers, mid 30s to early 40s Philcos generally STINK to work on!

[Reece]

Agreed. You do it by "neighborhoods." Divide the chassis into small areas and take a close photo of each section before starting. Then finish wiring one area as photographed before moving to the next. Take loose one end of an old wire but leave the other end connected: solder in the new wire and then route it to the other terminal where you finally remove the other end of the old wire. Best way to avoid mistakes. Follow the original lead dress to avoid feedback or hum problems. On a transformer-operated chassis, I like to make up twisted pair from hookup wire for the heater circuit to run from one socket to another where possible, ditto on runs to the power switch, all of which reduces possible hum. Can't do this with series string heaters where it's best to follow the original routing, which tends to put the first audio heater in a spot where hum should be the least.

[Winky Dink]

Gotcha, thanks. I have many 'before' photos, but should have taken even more when disassembling components.

[Electronic M]

Originally Posted by Kamakiri

Agreed. Just be thankful that you're not doing a 37-650. There are caps in that thing that I swear were installed before the chassis metal bending was finished. Between rotted rubber wiring and bakelite block condensers, mid 30s to early 40s Philcos generally STINK to work on!

Ditto on the rubber wiring being a pain in the neck. Though I've always liked the block caps. The Philco Repair Bench site has a good deal of info on what is inside them, and the tar filled ones are a snap to rebuild...Just unsolder everything, pry the tar out with a flat edge screw driver, and stick the new caps in. You don't even need to refill them with wax/tar because the open end buts up against the chassis preventing any view inside in most cases.

[Winky Dink]

I've used the Repair Bench extensively. I couldn't have figured out the block caps without Service Bulletin 289. And here's something you don't need to know--that black stuff in the blocks is wax. That's why it's easy to take out. If the part number starts with the letter "O," then it's high-temperature wax which might be a little harder to remove.

[boora2]

My 9yr ol girl rewired a Mickey Mouse tube radio,told her to be careful as it has an auto transformer,chassis could be live,it looked good too,turned it on,no work it was the kind that had a solenoid driven by a 6V6 to move the ears almost together when the station was correctly tuned,turned out a winding from the third if trans was open circuit,she pulled every thing apart until her cat kept flicking his tail against the trans,then the penny dropped,2 turns off to locate the break,slight retune,everything ok,the cat likes to watch the ears move.

[init4fun]

Originally Posted by boora2

My 9yr ol girl rewired a Mickey Mouse tube radio,told her to be careful as it has an auto transformer,chassis could be live,it looked good too,turned it on,no work it was the kind that had a solenoid driven by a 6V6 to move the ears almost together when the station was correctly tuned,turned out a winding from the third if trans was open circuit,she pulled every thing apart until her cat kept flicking his tail against the trans,then the penny dropped,2 turns off to locate the break,slight retune,everything ok,the cat likes to watch the ears move.

And again , In my best Mike Myers as "Dr Evil" accent ;

............ "RIIIGHT"

[Reece]

Cabin fever must've set in: gonna be a long, cold winter.

[Winky Dink]

Finished the chassis rewiring. But I'm left with two concerns before I proceed.

First, I'm over-thinking the instructions for one of the mid-model changes, and now I'm seeing two possible meanings.

"Beginning with run No. 3 resistor (16)…(51,000 ohms) was removed and a resistor…(32,000 ohms) was connected from the oscillator grid of the 6A7 to the suppressor grid of the 78 RF amplifier."

The question is, when I remove resistor (16) do I break the connection or do I leave the connection intact with just the resistance removed?



Next, I can't figure out what the connection (tap on the output transformer, yellow circle) represents. I have a four-pin speaker plug--two for the output transformer and two for the field coil (red circles). So, how does the fifth connection to the output transformer occur?



Thanks for looking. If I can get those issues resolved, then I can move forward with the restoration.

[old_tv_nut]

Remove means no connection - otherwise they would say replace with a wire.

[maxhifi]

Follow the wire from the top of the field coil and you will see it is the same wire that connects to the output transformer centre tap... only need a four pin plug here

[old_tv_nut]

Your 4 connections to the speaker are the two circled field coil connections, and the two output side connections (to the right of the two circled plate connections). In other words, the upper two red circles in your schematic are on the input side of the transformer and are not connected to the speaker coil. Your output transformer should have five connections - the two plates (red circled) and the center tap (yellow circled) - none of which should go to the speaker plug, plus the two output side connections (not circled) that do go to the speaker plug.

sorry I can't make a drawing right now, hope you get what I'm saying.

[old_coot88]

Just to simplify, a quickie sketch..