[Ron Ramirez]

Thanks, Mike.

I rebuilt the dial lamp socket assembly (two sockets on a common bracket) last night. The barrel-shaped parts that hold the lamp in place had both broken off at the bracket, so I glued them back together. They seem to be holding together OK. I used heat shrink tubing to replace the old plastic insulation that had surrounded each socket, and installed two LED lamps.

Today, I tried the radio out. Unfortunately...no go. Everything lights up, but there is no sound save for a very faint hum. When a radio won't even pick up my SSTRAN at 660 kc, I know something is wrong.

Well, the troubleshooting will begin over the next few days.

[KCMike]

Keep us posted on what you find out to be the problem. I like learning about different radios and thier problems.

[Ron Ramirez]

Bad news...

I did some checking tonight. Other than a weak 6A7 and a weak 43, I could find nothing amiss.

I replaced the 6A7. I do not have a spare 43 so it stayed.

No improvement. Plate voltage at the 75 and 43 tubes is normal. Placing a finger on the 75 grid cap results in a hum that is so weak, I have to put my ear up to the speaker to (barely) hear it with the volume control at max.

So, I decided to measure between B+ and B-, where the speaker field is (or should be) connected. It should read 2600 ohms. I read...infinity. An open field coil would equal a (virtually) dead speaker. Without an energized field, there is no magnetism to make the speaker voice coil work.

I see that I never did post a schematic or a link to one, so here's one at Nostalgia Air:
http://www.nostalgiaair.org/pagesbymodel...013796.pdf

A speaker from a 602 or 37-602 would be electrically equivalent, but I do not know if the mounting would be the same. I used to have a 37-602 speaker, but I can't find it now. I must have given it away with several other speakers a few years ago (and I still have too many speakers). I seriously doubt that I would find a speaker from a 604 or 37-604, as popular as those sets are.

I could even use a PM speaker in this application, since the speaker field in this set is only there to energize the speaker, not serving any other purpose. But the mounting would be a problem. The 604 speaker uses special brackets or "ears" if you will, attached to the field "pot", to hold the speaker on the chassis.

One more thing. I'm using a 6.8 megohm resistor in place of the nonexistent bias cell, although I do not think that is a factor at this point.

[KCMike]

Boy, thats not good news. Maybe someone here on the phorum will have one.
I know that is one I don't have.
Is it possible to rewind that field coil?

[Arran]

Boy, thats not good news. Maybe someone here on the phorum will have one.
I know that is one I don't have.
 Is it possible to rewind that field coil?

 Rewinding the speaker field coil is a possibility, provided that you can remove the coil and form from it's bracket. On some speakers you can unbolt this bracket, but on others you would need to use a press to press out the pole piece from the center to get it out, that is if it's press fit in there and not welded in.
Regards
Arran

[Ron Ramirez]

Based on other smaller Philco speakers I've seen, I suspect the field is welded in.

I'll remove the speaker this weekend and take a good look at it (and post photos here).

While it's out, I should connect it to my signal tracer, using its Test Speaker function (in other words, using the signal tracer's speaker as a test speaker) and see if the radio will play. The radio does not need a field coil for anything other than to energize the speaker, so if the radio works, the test speaker will let me know...and if not, I can continue troubleshooting...

[GarySP]

Good luck with that speaker, Ron.  Maybe you can get lucky and only have a bad solder joint at one of the lugs.  How are your metal working skills?  Perhaps you could fabricate a cradle to adapt another speaker to the chassis. I'm sure you're not going to let something trivial like an impossible to find speaker stop you!  Take care, Gary

[Radioroslyn]

How about a spkr from a 600, 602 ,37-600 or 37-602??

Terry

[Ron Ramirez]

A speaker from a 600 or 37-600 would not work - the field coil in those is rated at 1140 ohms. The 604 requires a field of 2600 ohms. A 602 or 37-602 is electrically equivalent, but I'm not sure about the mounting.

I'll remove my 604 speaker tonight or tomorrow and post some photos of it, showing how it mounts on the chassis.

[Ron Ramirez]

Hold the phone, everybody...

The speaker is OK. Some dummy (me) just connected one wire in the wrong place and then made an inaccurate measurement.

Really...it looked like those two wires were coming from choke (60), not from the speaker field. DUH. Well, even an old man who has been in the hobby for 41 years can make mistakes.

The radio is still silent, although it now produces a louder hum at the grid cap of the 75 tube (I think it should be louder still, but at least it is an improvement). It receives nothing. No AM noise. No SSTRAN at 660 kc. Nothing.

I plugged the 604 into an isolation transformer and started to hook up my signal generator. But when I attached the ground lead of the signal generator to the chassis (as the Philco specs call for)...the GFCI which protects the basement outlets tripped. So much for that. Now I'll have to figure out how to align this D**n thing...that is, if I can even get it going again.

Perhaps tomorrow, I'll put a small, working radio next to this 604 and see if I can pick up its oscillator in the working radio.

I sincerely appreciate the PMs with offers of speakers. Thank you...but I do not need one after all.

[Ron Ramirez]

AT THE WORKBENCH - I have just taken some more voltage measurements, and made a startling discovery.

There is no voltage at the plate of the 6A7.
No voltage on its screen.
No voltage at the oscillator "plate".

What the heck?!?!?

Well, I'm going to dive back in and see what's going on...perhaps another wiring error...

[Ron Ramirez]

Found it. Choke (59), 2250 ohms, is open. This kills B+ to the det-osc and IF tubes. No wonder it won't work!

[KCMike]

Sounds like your closing in on getting it to sing. Good luck.

[Ron Ramirez]

Looking around in my stash o'stuff, I found a 2200 ohm chassis mount resistor. 50 watts, which is overkill, but hey, I have it so I tried it.

Worked like a charm...the radio now picks up my SSTRAN and I can barely hear a few other AM stations with my ear close to the speaker...

As a refresher, here's how the chassis did look:

[Image: http://www.philcoradio.com/images/phorum..._00021.jpg]

and how it looks now:

[Image: http://www.philcoradio.com/images/phorum..._00023.jpg]

[Image: http://www.philcoradio.com/images/phorum..._00024.jpg]

And here is the open choke:

[Image: http://www.philcoradio.com/images/phorum..._00025.jpg]

Unfortunately, we're not out of the woods yet. The volume is very low. Could very well be the missing 1 volt bias cell, although with a 22 megohm resistor in place of the bias cell and the 1 meg resistor, I measure 1.1 volts on the grid of the 75 tube. I even "borrowed" a good 43 from my restored and working 38-14CB, and it didn't make any difference.

And there's still the problem of alignment. I tried isolating the radio from both high and low leads by using two 0.1 uF caps in series with each signal generator lead, but that made the GFCI outlet that protects the basement outlets make a weird buzzing noise, so I quickly disconnected it all.

Any advice welcome...

[Radioroslyn]

So how's the plate and SG voltage on the 43? Measuring from the cathode - and the control grid+ what do you see?? Plate voltage on the 75 OK?

Terry