Love that pic of the little guy working hard on that project of his! Peter I forgot to thank you for the info on the bumblebee and the color chart.... very helpful info. I suspected that bumblebee was a safety cap since it was across the AC lines. I'll test it and only replace it if it's bad, but I've got a few "Y" type safety caps that might work. I've had an exciting week. This weekend I purchased a ton of stock from an old radio/tv guy at auction.... 4 pieces of Conar kit equipment w/manuals and a about 100 tubes, 1000 ceramic caps and resistors. Then I managed to fix my first broken coil on a magnificent tiny Japanese "Monarch" radio. I just could not believe it when I heard that thing crackling back to life! What a great feeling! I'm hoping the parts for this GE 447 arrive while my luck is holding out..... I don't know what the hold up is on them.... Anyway tonight I'm going to take one of those coils apart and see if I can find the SMD on the capacitor.... 10 days ago I wouldn't have touched a coil with your soldering iron, much less my own! Now I'm diving right in! Thanks for the confidence.

Norm, Thanks for the tip on the lamp. I think I did replace this rectifier twice so far..... I didn't know why but was suspecting some other electrical problem. Now I think it might have been that the lamp was burned out. I'll replace that immediately.

Those bumblebee type capacitors have a nasty habit of shorting out (I had one do that). They are definitely not safety rated. When connected as a line bypass they are particularly dangerous. In that location, I would replace it whether it tests good or not.

-David

If you ordered the parts from Futurelec... remember they are in Thailand.. so it may be a cpl weeks.

OK.... Pulled the 447 off the shelf tonight to check the caps inside the coils. I discovered that at some point over the last two weeks I must have "borrowed" the 12BA6 tube out of it without replacing it. So before I got started this evening I put an NOS 12BA6 in it and VOILA! It started working! (Albeit at a low voltage of around 80 or so.)

In fact it was working very well for about 10 minutes. A few days ago I did receive replacement caps for the multi-cap-unit thing in the output section and so I decided to replace those tonight.

But afterwards I plugged it back in again and suddenly there was only the crashing - clicking noises from before!?!?!?! I was a little baffled. But the new caps are in there correctly. I shut the radio off and discovered that I must have inadvertently switched the "Phono" switch to "Phono" instead of "Radio" while soldering. I switched it to the correct position and turned the radio back on. It worked great but with problems. The slight humming and white noise were now gone, no doubt due to the new caps in the output section. But I turned the voltage up to 110 and in about 10 seconds the rectifier tube (35W4) burned out.

So I replaced the rectifier tube and lowered the voltage again to around 80 and it ran well for about 15 minutes until I shut it off. I suspect some problem in the rectifier circuit.

I shot a short video of this (success/Failure???) and posted it on youtube. You can check it out here:

http://youtu.be/rhO-joXPps0

Hope you'll have a few minutes to watch it......

John

Hi John:
I don't have that print... but probably the rectifier blows because you do not have a pilot lamp in its socket... and the current is too much on the filament without that parallel lamp.
If you don't have a spare lamp to use while testing you could probably use a 33 or 47 ohm 2 watt resistor jumpered across those same lamp-pins on the rectifier to protect the tube until you get the correct lamp.

Codefox:
Is it time for whom to do what? What's your point??

The total posts here are a combination from two separate guys ( mugginsjr & Exprof ) who are individually working on two or 3 radios. They are both very nice intelligent & diligent noobies.... doing their level best to learn and make progress!
.. so you would have had to have properly read the whole thread Codefox to make any kind of an informed comment.

Thanks Peter for the resistor/lamp substitution idea. But I do have the replacement lamp and in fact had it in when the rectifier blew the last time. So I'm thinking it might be another problem this time. I'm going to recheck all the resistors again and probably replace that bumblebee with a safety cap.

I don't mean to add yet another post to the fray. I can understand that it can be irritating to some to see the same old topic over and over. And I apologize to anyone offended by that. But the truth is I have not had more fun at any other project I've ever taken on. Working on this radio (now my 8th restoration) has been a great source of enjoyment, and even though it's just a cookie-cutter 1955 tabletop model I still will not acquiesce and let it fall into the junk pile. The whole reason I'm working on these wonderful little models is to get through my learning curve on radios, so scrapping them would kind of defeat that purpose.

Thanks to everyone for your patience. And for those of you who went out of your way to help me with your invaluable experience: thank you sincerely. This 66 or 67 post thread has been a wealth of knowledge and insight for me. There's no way to repay that kindness except to say thank you again.

John

Hi John:
FIRST... I feel I speak for the majority of the members here when I say that you do not need to apologize for asking ANY questions at any time as many times you you wish.

Codefox was out of line with his comments.

That's a shame.. It's EXACTLY those asinine-type comments like that by Codefox that cause new members to be afraid to ask questions..
He ought to apologize because HE too was a beginner once and surely asked questions I'm certain.
I feel it was rude and rather "smug" of him to assert himself here and try to intimidate you and Exprof by trying to show off his unintelligent, smart-alecky ways.

But it only serves to show how unkind he is and nothing else.

It's my FIRM belief that no one has to right to attempt to intimidate ANY one else here for any reason at anytime.
He was simply way out of line.
I'm sorry John that you had to encounter that level of rudeness here.
Please do not let it deter you from asking ANYTHING ever.

Now back to your problem:
(BTW.... May I assume you've already replaced the electrolytic filter caps in the power supply? If not do so. Also replace that bumblebee cap ( it is NOT the cause of your current problem) but.. it is a "paper/foil" type cap and ANY paper-type caps always should be replaced regardless of if they test good or not.)

When I saw the video I thought I noticed the empty lamp socket on the dial pulley... right?

Well.. when you say "the rectifier blew" .... you probably mean that the filament "blew" or "opened"... right?
If you use your ohm meter to check the blown tube. You'll probably find that filament section between pins 4 - 6 is the "open" section and that the section between 6-3 still has continuity.

If 4-6 is open that means the tube was operated without the lamp for some period of time stressing that section.

In the following link, you will find a great multi-part tutorial on the AA5 radio John.. and this particular section here describes the rectifier tube theory as it relates to the lamp and how it works in conjunction with the filament tap:
http://www.angelfire.com/electronic/funwithtubes/AA5-1.html

This is YOUR radio:

Thank you Peter. But no, Codefox didn't bother or intimidate me. Though I'm a novice here I actually am an expert in other fields and so I can sympathize with certain annoyances we encounter sometimes and fully can see where he is coming from.

The lamp was indeed missing during part of that video. My intention was to shoot a short clip of video featuring crashing/static sounds for the beginning of a video. The ultimate purpose of that video was going to be to show Ex_prof how to take the coils apart and examine the foil caps inside. (sort of a learning experience for us both.) And I wasn't really prepared for the thing to begin working, so it took me by surprise.

I remembered what you and Neal told me about the lamp, so after I realized the thing was working I did replace it later in the video, though it is very dim inside that black tube. At 80 volts you could just barely see it as I spun the tuning cap around to a certain angle. Shortly after that (and off camera) I turned the voltage up to 110 (which is the last test I do for all radios) and 10 or 20 seconds later everything died. I immediately suspected the rectifier - stuck a new one in there - and turned the voltage back to 80 and it seems to work fine at that level. But the new lamp definitely was in there when it died.

I didn't check the tube, since the replacement made it work I assumed it was burned out. I'll check it when I get home. There should be a short between pins 4 and 6 you think? For all I know the tube might be still good and maybe 110 volts did something else to the radio to shut it down..... I have a little tube checker, Sencore Mighty Mite, which seemed like a pretty good one but it failed to find fault with this 12BA6, I think. I'm sure I would have checked all the tubes and replaced all the paper caps before I turned this thing on to begin with.

Any way, I picked up 30 to 40 lamps from an auction over the weekend, along with about 1000 ceramic caps and about 1000 different resistors, all separated in little drawers of organizers. Also picked up a Conar cap/reistor checker, Conar Signal Generator, Conar Signal Tracer, and a Conar TV/Generator. (ALL kits with original manuals) It's like the guys whole shop was for sale. Also got about 60 or 70 tubes, transistor checkers, various other little dmm's and whatnot. .... I can't believe my luck this week! And now this radio appears to be almost fixed! I'm buying a lottery ticket tonight!

I said that normally there is continuity from pin 4 to pin 6 ... but if the tube was operated without the lamp for a while that section would have been over-stressed and so if the tube "blew" then you'll probably now measure an OPEN between pins 4 and pin 6.

The other part of the filament from pin 6 to pin 3 should still probably have continuity.

BTW.. have you replaced the electrolytic filter caps in the power supply yet?

Hey Peter.... yes, right, pins 4 and 6 of the burned rectifier are open.

But I am really happy to announce that the radio chassis is just about finished. Tonight I found a cold solder joint on the new ceramics that I put in yesterday. It was a circular kind of solder that was sliding freely over the 7 pin of the output tube. The other end is hooked up to the rectifier tube. I'm suspecting that is probably what burned out the rectifier. Oh, and the new lamp that was put in yesterday burned out with the rectifier as well. I repaired the bad joint, as well as the bumblebee across the AC lines, and it tested well for about 30 minutes at full power this evening. The new lamp is burning brightly, just like it's supposed to.

There is only one little problem with this radio now: There is a very slight hum and white noise in the background, even on the clearest stations. (Which are coming in magnificently.) I ran a signal tracer through it briefly, but my ear must not be trained well enough because I was hearing one hum or another in all stages. Do you suppose it could be a resistor causing that?

On another thread yesterday I saw some advice about shorting out the plate and cathode of the IF tube and how if that stops the hum then the hum is before the IF tube. But if it doesn't stop the hum then it must mean the hum is somewhere after the IF tube. Is that true? Can I do that without damaging the tube? Also, would that same technique work on the other tubes?

Thanks again,
John

You never answered if you've replaced the electrolytic filter caps.

If you have not yet replaced them.. do that as a must.
Electrolytic caps from years ago are the 1st to start leaking and draw excess current and that will cause poor AC filtering also generating hum.

It is NEVER EVER a good idea to short or ground the plate of a tube. The plate usually has high B+ voltage on it, and shorting that will wreak havoc.

Each stage of the tube amplifier including the IF stages are (DC wise) safely coupled from the Plate of one stage to the Grid on the next stage. The (isolated) coupling is either by transformer such as an IF transformer or by a capacitor such as the one feeding the input grid on the 50C5 output tube.

When you are trying to locate the source of a hum or other noise on the signal path.. you can ground the GRID of each stage, thereby quieting anything from there toward the output.

So if you have an unwanted buzz or hum on your signal.. you can start tracing it by 1st grounding the grid of the 50C5.
If that is quiet.. then you know the hum must be before that point. So you can then ground the grid of the next earlier stage and so on working from the output stage back toward the input RF section.

Sorry Peter, must have overlooked your question about the electrolytics. But yes, one of my first few steps on a new project is always replacing the caps before plugging it in, especially the electrolytics.

And thank you for the tip on shorting the grids to find the hum. I'm glad I didn't follow that other advice about shorting the plate to cathode.

I'm really excited that this radio is well on the road to recovery. Thank you for all of your help. Your advice and kindness are much appreciated. I haven't heard from ex_prof though. I was wondering if his problem might be tied to the 12BA6 tube as well.

Apparently I spoke too soon: when I returned home this evening I turned on the radio (cold) at full 110 volts. The lamp went super bright and burned out in about 2 seconds. I shut it off immediately but not quick enough. Another 35W4 rectifier bit the dust. I replaced it with my last and fourth good 35W4 tube. If I start the radio at 60 volts and gradually increase to 110 it works ok, but now the lamp is extremely dim, just an orange glow on the filament.

There is some kind of surge problem burning out these rectifiers. I don't think it is from anything I've done. I've checked and rechecked all the connections on my replacement caps and they are all correct.

There are two anomalies probably worth mentioning, but I don't know if they are important. I replaced a .047uF bumblebee cap across the AC lines with a .1uF safety cap. Could that be causing the problem? I don't have any .047uF or ,05uF safety caps on hand. Secondly, there is a .02uF cap that I replaced between the center volume lug and pin 1 of the 12AV6 detector. Just incidentally I had run out of .02uF caps so I connected two .01uF caps in parallel. But that's neither here nor there. The thing that i just noticed is that the markings on these two caps, (the black ink that shows the uF and voltage) are completely gone - like erased - from one of the caps and mostly gone from the other! These caps were fine when I installed them..... What caused the ink markings to disappear? Could they be getting very hot or something?

Here's a photo of part of the chassis I threw together from a few grabs from a video;

Sorry there is no picture

Thanks for the video, John; it's encouraging to see your progress. My radio has an RCA jack, but no switch.

I ordered some caps, and I'm waiting for them to arrive so that I can refurbish the IF cans, so I'm still on hold here.

Peter: thank you once again for your help and words of support

Hi John
That (c-13) 0.1uf @630vdc cap across the AC line is probably not a problem but if you place another 0.1uf cap in series with it across the line you will have a combined cap = 0.05uf @1260v. That will be safer.
Are you using a #44 lamp or a #47 lamp?
The print calls for #44 lamp which can carry 250ma whereas the #47 can only carry 150ma.

To help you troubleshoot and not blow more 35w4 tubes ... you can probably use one of the already blown tubes for testing purposes by temp connecting an alligator lead across pins 4 and 6.
Remove the bulb.
This will by-pass or jumper across the "open" section of the filament and the tube should still operate alright.

In this configuration you will be able to take some test readings with the Variac at 120volts AC.
Put your multimeter in DC ma mode and connect it in SERIES with the RED wire going to the output transformer.
You should read around 60ma if the radio has a normal B+ load.
Measure the plate of the 50C5 for 120vDC and the cathode for 6vDC.
The screen grid pin 6 should read about 90vdc.
MAKE sure you have the polarities on the two electrolytic caps C-16-A and C16-B connected properly.

If your B+ current exceeds 60ma by any real significant amount, then there is something shorting in the B+ circuit.
There could be something like a short in the output transformer or elsewhere.



SUGGESTION:
==>>To avoid blowing out more 35W4 tubes while you do your troubleshooting, ....Another thing you can do is to remove the 35W4 tube completely and without the #44 bulb either.
Then use TWO 1N4007 diodes to take its place.
1.) Connect one diode as shown across pins 4 and 3. That will provide about 84volts of pulsating DC to properly operate the balance of the filament string when the 35W4 tube is no longer there.

2.) Connect another diode across pins 4 and 7 in the direction shown below. This diode will replace the rectifier action of the 35W4 completely.

In this mode you'll have a properly functioning rectifier for DC (although B+ will be a bit higher)
.... and your filament string balance will operate as well.

This substitute device can be made easily and inserted from the top of the socket.
Just solder the two anode ends of the diodes together to form a "Y"
....so you'll have only one common anode lead to insert into pin 4 from the top side of the socket.
Then you can insert the cathode end of one diode into pin 3 and the other cathode end into pin 7

At this point again you should be able to do all your testing and troubleshooting until you get the radio to a stable condition.
After troubleshooting and once everything is operating properly... you can remove the two diodes and reinsert the 35W4 and #44 lamp.

Peter, you are an absolute genious! Crossing the 4 and 6 pin of a dead rectifier will save me from burning out any more of them! I don't know how to thank you for all this advice. I'll just be extra careful and make sure that I don't start it at full voltage while those pins are jumped. I'm busy most of today helping a friend with her car problems, but I'm itching to get home and perform these tests.

I want to mention this again because I agree with your suspicion there is a B+ short. When I turn the voltage up over 110 volts I get intermittent crashing/clicking sounds and significant loss of signal, pretty much just like before, although the signal is still a tiny bit audible. As a novice I'm still suspecting SMD and that the short is in the IF coils. While running the unit at around 65 or 70 volts I'm getting B+ voltage on the primary side of each coil at about 29 or 30 volts. The secondary side of each coil is showing very low negative voltage, like around -.25 to -.6. As I increase the voltage to around 110 the secondary coil voltage jumps up to around -3 or -4 volts. Is that normal? Since the output of the coil is going to the grid of the following tube I think it's supposed to be negative, right? I'm pretty certain that before I replaced the 12BA6 tube I was getting positive voltages on the secondary coils, when the ONLY thing that could be heard was crashing/clicking sounds.

Anyway I'm going to follow your protocol of tests as soon as I return. I've looked your thoughts over and think you are absolutely right. Somewhere in those tests we're going to find the answer.

Ex_Prof: Hang in there... We've made a lot of headway so far on the 447 and it's apparent that whatever went awry with it caused several components to go bad or out of tolerance. So far I've been able to treat the "symptoms" one by one until we have a working, testable radio at about 60 or 70 volts, but haven't yet found the root cause. But it looks like we're getting really close to a "cure!"

Shorting between pin #4 and #6 will get the filaments operating again. If no no other problems B+ will be present.

There is one disadvantage. This section of filaments acts as a fuse. If something shorts it blows. Without it, no fuse.

A lamp in series with the AC line would be a good idea. It will light bright if something shorts.

John:
If you didn't scroll down enough you may have missed the second section of my post above:
I'll repeat it here:

SUGGESTION:
==>>To avoid blowing out more 35W4 tubes while you do your troubleshooting,
....Another thing you can do is to remove the 35W4 tube completely and without the #44 bulb either.
Then use TWO 1N4007 diodes to take its place.
1.) Connect one diode as shown across pins 4 and 3. That will provide about 84volts of pulsating DC to properly operate the balance of the filament string when the 35W4 tube is no longer there.

2.) Connect another diode across pins 4 and 7 in the direction shown below. This diode will replace the rectifier action of the 35W4 completely.

In this mode you'll have a properly functioning rectifier for DC (although B+ will be a bit higher)
.... and your filament string balance will operate as well.

This (two-diode) substitute device can be made easily and inserted from the top of the socket.
Just solder the two anode ends of the diodes together to form a "Y"
....so you'll have only one common anode lead to insert into pin 4 from the top side of the socket.
Then you can insert the cathode end of one diode into pin 3 and the other cathode end into pin 7

At this point again you should be able to do all your testing and troubleshooting until you get the radio to a stable condition.
After troubleshooting and once everything is operating properly... you can remove the two diodes and reinsert the 35W4 and #44 lamp.