[Pithicus999]

Hi,

I’m repairing an old philco model 18 (code 121). This radio is my dad’s and as far as I know it has never worked as long as I’ve been alive. So I decided to skip the trouble shooting and just go ahead and replace ALL of the capacitors and ALL of the resistors. I also repaired a ripped speaker, and rewired the speaker and outlet plug.

I fired it up, and there was sound, the light went on and all amp tubes are lighting up (orange glow really, had to replace 2 of them). However, there was a low sounding voltage drop—is the best way to describe it—and then no sound at all. I turned all the dials, and nothing more happened.

My next thought is to go through each connection, one by one, and verify that everything is connected to the proper capacitor, resistor etc. But before I do that, I thought I’d ask you for your thoughts?

Also, I took a 30 second video where you can see and hear what is happening. But this site won't let me attach it. What format does it need to be in? I tried changing it to 'mp4' but that didn't work. It's from my iphone and is a '.MOV' file.

I appreciate any help anyone can give me.
Thanks.

p.s. I'm totally new at this, but I am good at following directions. I printed the schematics online and have been using them as best I can. Some stuff though, I don't know what the heck it means.

[DKinYORKpa]

I have a working 18 upside down on my bench right now. Do you have the electrolytics hooked up correctly? Did you take out the 80 tube and check the voltages to its pins? I'm no electronics guru, so your symptoms do not mean much to me.

[Ron Ramirez]

Pithicus - Welcome.

You cannot upload videos directly here - you have to put them on a host such as YouTube, Dailymotion, MetaCafe, Myspace TV, Vimeo, or Yahoo Video.

Once you have done that, you can easily link to the video by clicking the down arrow next to the little TV icon you see when you are writing a new reply (or starting a new thread), clicking the host name, and then inserting the URL where the video is hosted. This will allow a small window within your post where folks can watch the video without going to the host to do so.

Sounds to me like you got a bit ahead of yourself. One should not ever work on electronics without taking the time to learn the basics, how to read a schematic, etc. I'm not being critical - just being honest.

Some great info for the beginner may be found here:
http://www.antiqueradio.org/begin.htm

Your next step, once you have familiarized yourself with the basics and how to read schematic diagrams, is to find out just what went wrong, or if there is another issue keeping your radio from working. A signal tracer, signal generator, and multimeter are essentials tools to assist you in this endeavor.

Another thought: You live in a state which has a very active antique radio club. I suggest you join the Michigan Antique Radio Club.

http://michiganantiqueradio.org/

They may have one or more members living near you who may be willing to be a mentor to you as you get started in this fun and exciting hobby. Plus, we're here to help also, and glad to do what we can.

[morzh]

If you can post the video and provide the link, I will try to make sense of it.
I also have an open 18 (124 but the differences are minor), that works (waiting on the shadow meter replacement).

Also the advice Ron gave you - heed it. Unless you know something about electronics and especially about tubes, as the voltages there can simply kill you, don't just go in and try to fix stuff. Read something first. You have to know at least some basics.

[Pithicus999]

Wow, you guys are great, thanks for the quick responses!

DkinYORKpa - When I replaced the elec caps I cut one at a time and replaced according to the schematics. I do have a multimeter that I will use to check the voltage on the 80 per the scematics (should be 350 if i'm reading this correctly) I can tell you that all tubes are glowing orange when radio is turned on.

Ron - You are probalby right. I did take physics and electronics in college but that was years ago. I just was excited about this thing actually working some day! I actually think i've learned a lot so far. I've been working on this since November 2012 and been checking out youtube and read some posts. I'll try to put that video up on youtube tonight.
Thanks for the advice!

morzh - I was reading something today about adjusting the compensating condensors. I thought that might be the problem, when I went to adjust them (looks like there are 4 of them? 2 on the back under electrolytics and you can reach them from the back with a 1/4 socket I used 9mm instead and 2 on the bottom) anyway, it looks like I need a signal generator to adjust those properly.

All - I looked online for a signal generator and they are expensive. Any ideas?

I'll try to attach a video...

[Pithicus999]

[Video: http://www.youtube.com/watch?v=PJRewmPhnZM]

I've attached the video that is giving me the crazy 'train' doppler sound.

I also have another much more boring video showing what I've replaced on this radio etc. try not to fall asleep.

And here is that video
[Video: http://www.youtube.com/watch?v=E5-H1lRdh1o]

Thanks.

[DKinYORKpa]

I see a mistake. That 10 uF, 50V electrolytic on the left side of the chassis in the video has the polarity reversed. Its positive should go to chassis ground. And the negative joins the negatives from the two 8uFs. Somebody correct me if I'm wrong.

[Ron Ramirez]

Absolutely right, DK.

[TA Forbes]

Good catch, DK! That is what I was thinking.

When one is new to the hobby it is common to believe that ALL electrolytic negative sides go to ground, which is not the case.

[Electrothaumaturgist]

I haven't put an electrolytic in backwards (Yet-knock on wood), but heard that they'll explode or pop if incorrectly installed. How come his didn't? (Just wondering?).

[Ron Ramirez]

Probably because of the low voltage involved (on the order of 25 volts or less). I've put these bias filters in backwards before, in my younger whippersnapper days, and they didn't pop. But put a main electrolytic filter in backwards, power up, and they go BANG like a gunshot...

[Electrothaumaturgist]

Thanks Ron. Good to know...

[Conelrad]

That feedback squeal upon turn-on is most likely caused by an incorrectly installed bypass cap or maybe the speaker wiring being redone to wrong pins.

Dennis

[Pithicus999]

Again, thanks for all the quick responses.

Well, I did think that all negative sides went to ground…

Questions:

1) Everything I’ve read says the (-) side always goes to ground. The only thing I can think of is that if electricity is flowing in the direction of the arrows, when it’s hooked to ground, it’s leaving the circuit via this 10 ufd cap—and therefore not working. Before I reverse that cap (because I don’t want to get killed or have a heart attack if it explodes) what explanation can you give to reassure me that it needs to be (+) to ground in this case and that I don’t need to update the beneficiary on my life insurance policy?

2) Are my other (3) caps ok if they have the (-) going to ground? More specifically on the schematics side of things, this is what I have:
a. # 53 & # 54 have their (-) arrow side going to # 55(Like DK already pointed out) which is the 10 ufd cap we are talking about. Are these two (# 53 & # 54 ) hooked up correctly?
b. # 40, now from what you said about the 10 ufd, I’m a bit worried about this one. On the schematic for # 40, it shows a 1 ufd cap hooked up to two resistors on one end (I’m thinking the positive end because I thought (-) negative side goes to ground) and hooked up to ground on the other end. According to what I’m hearing from you, it sounds like you are saying that the (+) positive end of this 1 ufd cap should go to ground instead of the way I have it????

Conelrad – With the speaker wires, I was able to confirm only two of them while replacing them. I followed the 2 wires into the plug as best I could, however the other two became dislodged when I removed the casing. By default, since the other two wires are the ‘opposite’ ends of the two that I identified, they may have to be switched…of course now…I’m not sure which 2 of the four are good, and which two are bad.

p.s. I have the schematics on PDF if anyone wants to see them.
p.s.s I’m still having fun 
Thanks.

[Conelrad]

Some circuits will jack up the center tap (read negative return) of the power transformer off chassis ground through a resistor network to get a bit of negative polarity bias voltage for final amp tubes, or sometimes the AVC function.

From your perspective, it is backwards to chassis as the voltage is 'positive ground'. Sometimes this is tricky to discern, and troubling to wrap your head around.

Take a closer look at your schematic and you will see the 'Ohms' I'm talking about.

Dennis