[Dbwaibel]

Last summer I stumbled across a $10 Philco console radio tucked away under a couple of worn out wooden lamps at a garage sale. While I do have substantial training with contemporary electronics, I have no experience at all with anything that predates the transistor, but at that price I had to give it a shot.

So far I have made two real mistakes: 1) I didn't remember to take a pre-teardown picture of the chassis until I had already un-mounted or de-soldered most of the wires from the Bakelite capacitor housing; 2) In the pictures I did take, it is not clear where the two black wires from the transformer are attached.

Regarding the black wires, I am fairly sure one of them solders onto the Bakelite housing at the terminal which has the grounding screw in it, but in the schematic I downloaded the other one (other end of the smallest coil in the transformer) ends with a symbol I do not recognize from school (the same symbol can be found on one end of the pilot lamp leads).

If anyone out there has a pic/drawing of how the Bakelite housing should have been connected up before dis-assembly, that would help me a lot at the moment.

Apart from that, I'm basically going through and replacing one rubber wire at a time: most of the ones near the transformers are badly shot but on the other side many of them still look to be on the dry side of usable. I've already gone into the power transformer and slid heat shrink tubing as far up the wires as it will go, however without a proper heat gun (I'm working on a computer desk in my apartment) I had to secure them with electrical tape rather than by shrinking. This has resulted in some longer lead wires than the originals... how critical is wire length for resonance in a system like this? I have also replaced the power chord it came with, which was itself a 1951 zip chord complete with a paper tag from the repair shop in Tracy MN that must have installed it (along with, I think, a newer Bakelite cap housing: this one has the yellow paint rather than the "hot stamp" on it).

Given what I have to work with and my lack of pre-transistor experience, my goal is to simply get the unit working while bolted into the original cabinet. If I have to replace a cap with something modern looking to make it work, than I will do so. On the other hand, there are indications that this unit has been overhauled before, so once I get the rubber wiring straightened out I may simply plug it in and see what I've got before trying to re-cap it.

BTW, is there any such thing as a cheap, reliable, short-range AM transmitter (something like the FM devices people use with iPods to make them work in cars that have very simple radios?). I've got several old computers here that I would like to try using to feed period-appropriate music into this radio without compromising the original electronics more than I have to.

[tab10672]

The schematic i am looking at, has the "chassis ground" symbol on each lamp. That symbol is universal even in modern electronics.

[morzh]

Just go by schematic. Things have not changed much since, a capacitor is still a capacitor, a resistor is a resistor. A wire will still conduct current.
Gut the backelite blocks, stiff with new caps, do not even pot them again.....
The voltages are somewhat higher than today's ones so be careful: even on the states' levels electrocution is no longer legal.

[Eric T]

Hello and welcome to the Phorum.

I have a 39-45, too. I'll be more than happy to get some photos of the chassis innards. You may have to wait until this weekend for me to get the time to pull it out of the cabinet. This is a great sounding, great performing radio. Restore/repair it right, and you'll want it around for a long, long time.

That being said,

RE-CAP IT! RE-CAP IT! RE-CAP IT! RE-CAP IT! RE-CAP IT!

Oh, yeah....

RE-CAP IT!

Those paper and wax caps are all bad. Even if they read OK, they're bad. The electrolytics are bad, too. This is a safety issue above and beyond a performance issue.

To your question about a cheap, reliable low-power AM transmitter:

You can buy a SSTRANS kit for about $90, which I hear are excellent units. I even plan to buy one myself soon.

Or, if your as cheap as I am, you can check out this thread at ARF and build a decent performing little transmitter for about $15. I'd recommend using an IC socket so you can change crystals easily.

[BrendaAnnD]

Can you take a pic of the area where you've removed the wires from the bakelite block? There should be several in that radio, and it would be helpful to know which one you're dealing with.

Lead dress in these radios is not critical, except to some extent in the RF/IF sections. The higher the frequency, the more critical it would be.

There are several low power AM transmitters available, but none are particularly 'cheap' (depending of course on your definition of the word). Cheapest you'd likely run into would be a Talking House transmitter. These are on ebay quite often, and you can get lucky and get one for under $50 if you keep an eye out.

[Raleigh]

The Bakelite block has 2 caps inside it. One end of each cap is attached to the ground lug at the screw end. One of the caps is attached inside to the middle terminal, and the other cap is attached to the terminal opposite the screw.

The original power cord was not polarized. If you want to connect it just as in the schematic, ignore polarity. One power lead goes to the middle lug of Bakelite, one power lead to the lug opposite the ground screw. One transformer primary lead to either of the Bakelite non-ground lugs, the other primary lead to the power switch. The other side of the power switch goes to the Bakelite lead that doesn't already have a primary lead on it.

If your replacement power cord is polarized, I'd do it a little differently. Connect the neutral power lead to either of the non-ground lugs on the Bakelite block. Connect the hot lead from the power cord to the power switch and then the other side of the power switch to the other of the non-ground leads on the block. Then put a transformer primary lead on each of the non-ground lugs on the Bakelite block. This gets your AC power off any components when your radio is "OFF."

I'm sure there is something grounded to the Bakelite ground lug, but I don't know what. Anything nearby that needs to be grounded could go there if there isn't another convenient ground point.

Are you replacing the rubber wires by desoldering them? If so, you might as well replace capacitors with modern ones at the same time (except the little mica caps that look like dominos) and resistors that are more than 10% out of tolerance. It's not much more work if you are desoldering anyway. Some restorers give resistors 20% and some replace them all, regardless.

It is most important to change the electrolytic capacitors with new 450 volt 'lytics before you even plug it in. They are no doubt dry and leaky. If they short, there goes your power transformer.

It's a good idea to replace the caps inside the Bakelite, too, because they will probably soon short or leak power to ground, and there goes your transformer. Replacing them is really easy, takes 15 minutes. You'd need to order modern Y or X/Y caps. And a lot of folks add a fuse to the hot side of the line, before the switch.

[Raleigh]

P.S. You can also replace caps and resistors by cutting out the old ones close to the component body and then solder new components to the old leads that remain. It's easier than desoldering them, but it doesn't look as nice.

[Dbwaibel]

Wow, that was quick. Thank you all very much.

Regarding the chassis ground symbol: I see that too, but what I was wondering about was the symbol on the other side of the pilot lamps. I did eventually figure that out by studying the tube schematics: it refers to a common power bus, apparently to drive the tube heaters, in the form of a red wire that's daisy-chained to all the tube sockets except for the rectifier (at least that's what I'd call it on a newer system). Once I saw this possibility, I went back to my original photos and realized that the original length of the black transformer wires was also about right for the nearest red wire terminal, and that there was partially removed solder on that terminal (I actually began this project in July, but had to set it aside for a while due to a death in the family). So now I've got one of the black (small coil) wires tied to that red wire bus, and the other end tied to the ground lug of the Bakelite housing where I believe it was all along.

As for the Bakelite housing, I like John's idea for a new polarized setup with fuse very much. I've tried to set it up according to the schematic, but I think there's a part gone missing because I'm ending up with an incomplete switch connection that way (one of the switch leads is attached to a terminal that physically mounts on the ground screw but doesn't actually connect to it: there's nothing there but wafer-board). Also, very suspiciously, I've ended up with both that black ground wire and one white lead from the primary coil competing for space on the ground terminal... this can't be right, but with the original switch leads being where they are (I never de-soldered them, and the plug wires are right where John is saying they should be), I don't see the alternative.

OK, I just tried to upload a fresh pic from my 5MP Kodak but I'm getting a message that the file is too big... have to work on finding a way to make smaller ones.

[BrendaAnnD]

640x480 or 800x600 pics work well here.

[hsusmann]

Re: an AM transmitter. I actually use my HP3325A function generator as an AM transmitter if I need one. This is another reason I like to use it for my signal generator. With the A version you need a 2nd audio signal generator also.

The HP3325B (later version) actually has an internal modulation source also so you don't need the 2nd audio osc.

Before anyone spends very much on a dedicated AM transmitter you should look at getting a used 3325A or B instead. They are great for doing alignments and as a general purpose function generator. Can't beat
the totally accurate frequencies you get and complete accurate amplitude control

Re: Minimal experience with vintage tube electronics and lots of modern electronics experience. I was like that also to some degree but always grew up with tube stuff in my teen years so always had some knowledge of the older stuff. My knowledge has increased 100x in recent years as I work on these old radios.

Best advice is to be careful of the high voltages, get yourself a variac and a way of putting a light bulb in series with the line cord when you first do a power up.

Always replace old capacitors no matter what. Electrolytics and paper caps. Micas are probably good although not always.

You are taking a huge risk by leaving in old caps. If the wrong one shorts out then you can take out transformers or coils or who knows what and then you may or may not be able to fix it again.

[Dbwaibel]

BTW, about how many amps would a thing like this draw through the fuse?

[Raleigh]

On the schematic, it says "Power consumption 85 watts." That's a nine-tube radio, so it'll pull a lot of power.

Use this calculator http://www.sengpielaudio.com/calculator-ohm.htm to calculate the current based on Ohm's law. Fill in your line voltage, roughly 120 VAC and the power, 85 watts, and it will calculate current for you. It's about .708 amp.

Someone on the forum might know what size fuse to use for this amount of current. Except for the power-on surge, your steady-state current will probably be a little less than this calculation.

All my larger Philcos are rated between between 60 and 70 watts. They pull between .4 and .5 amps, measured with an ammeter. I use 1 watt slo-blo fuses for all. Some guys use fast-blo. You might have to buy several values of fuse between, say, 1 and 2 amps to see what works, unless someone else can give better advice than I can.

[Dbwaibel]

How are these?

       

[Dbwaibel]

Thanks John... can't believe I missed that in the schematic, but it bodes well for the 1-2amp fuses and in-line holders I have on hand. :-)

[skyscraper]

1 amp will blow every time you turn it on from inrush current. Some tubes use almost twice as much power to heat up. 2a should work.