Philco radio cap problem
 

The Philco 41-842 that I needed help getting a diagram for is giving me problems .There is one particular electrolytic cap in the 1LB4 (output tube)heater line that keeps getting very hot. I have replaced it with a new, still tests good cap. The diagram calls for a 100 mf cap 25 volts and the original sectional cap had a 200mf 25 volt in there.I used my digital meter and it does not show ac from the plus or ground of the cap to chassis ground or with my test leads on the plus and ground of it. I show about 4 volts dc from the pos to ground. One side of the tube heater does go to a grid inside the tube.I am lost,since I am not overvolting the electro. and I am not showing AC either ,but if I unsolder one end and test it with my cap checker it shows good.There is also an electro. in the other leg of the heater and it stays cold.The radio is fully recapped, the original speaker is gone. I do not know what the resistance of the output trans. should be so I do not know if it is an issue.I do have a speaker currently hooked up to the secondary of the output Trans. and I have no sound , hum, anything.Any Ideas?

I forgot to add that this is an AC/DC/Battery set. The cap in question even gets hot when there is only the rectifier tube in place. The other caps are not getting hot though. This is the second rect. tube I have tried. Both were nos and tested good on a tv-7 tester.It is a 117z6 tube.The only thing that I can think of is the switch is bad that is used when you want to run it with batteries. I do not understand the switch as far as how it is shown and what makes contact when. The reason is the switch to me looks different than the pic on the diagram. The diag. pic shows 3 rows of 4 connections with 2 extra contacts apart from the rest and my switch has 4 rows of 3 connections without the extras.

I could not find a listing for a 41-842 but did find a schematic for a 42-482, If you are not running the cap at more than the rated voltage, about the only other thing that could make it get hot is incorrect polarity. Double check it.

Looking at the schematic I believe this set has a 'floating ground'. That is the ground is not on the chassis but at several points that are tied together. Sometimes a solder lug or a tube socket lug, or a combination. There is usually a capacitor and/or high value resistor to chassis to bypass ac line noise. One side of the secondary of the speaker transformer runs to chassis ground too.

These are a bit safer than the notorious hot chassis models. Of course if that capacitor to chassis shorts then all bets are off. There are special caps for that purpose.

Look at the chassis and try to find where the points for this floating ground are.

Are you using an isolation transformer? Recommended regardless of the set.

Here is a lower res version of the 41-842 schematic from another thread:

http://videokarma.org/showthread.php?t=246027

I have an AC-DC/battery set too so I'm interested in this.

The speaker secondary does not currently go to ground. With the original speaker missing the output trans. is just hanging. Could this be part of the problem?

I don't think so. It may be that one side of the secondary is tied to the transformer mounting. Do you have a scope you can put on the output?

I would first verify the power supply. Check for B+ and filament voltages. And then work forward to the output stages. You still have that hot capacitor that maybe an issue.

Another possibility you should consider is that there may have been others before you. Changes may have been made and not necessarily the right ones.

You can check against the schematic but that raises the possibility that there may have been production changes. In which case the schematic might not match.

What voltage do you measure directly across the capacitor, from positive terminal to negative terminal, not to chassis ground.

The B+ was 125. the filament voltage on the "hot" cap was 82 volts. well, It is in the filament line and is a 25 volt cap.That also explains why I noticed that I lost a tube in the output.No on the scope for right now, I can borrow one eventually

82 volts. Gee, Thats alot for a filament line of a 1LB4 tube. The cap is 25 volts like the diagram calls for. So now I think I have to find the fil. voltage problem.

Well, Whomever had this set before me added in a resistor that totally changed the filament line which I put back to the diagram. They also replaced one resistor with a high watt. "brown Bar" resis. and placed it on top of the chassis but did not make sure that the wires going to it did not rub off the coating and short to the chassis. They then also cut out caps completely and put them in a pile in the cabinet. Fun, huh?

Well I guess I do not understand one thing. I now know that the tube heater line is getting too much voltage. The diagram shows the output of the rectifier going to a 1,800 ohm res. then to the heater of the 1Lb4. That is the way this set is wired right now. Do I just need to jump up the res. to lower heater volt. or does this tell me that something else is going on?

So inspector, are you feeling a little like Columbo right about now? :smoke:

Yeah 82 volts on a 1.5 volt filament will shorten the life of a tube. Are you measuring that across the filament?

It looks like all the 1lxx tubes have their filaments in series and there is a voltage divider.

Are you seeing 125 volts at the plug? That might stress things too since the set is designed for 117 volts or so. Do you have a variac so you can back the ac line voltage off a bit?

I'm kind of a 'go-by-the-schematic' unless I'm experimenting. So my feeling is something else is going on. I would continue to trace out the circuit and see what else is different.

A next step might be to check the filament voltages for each of the tubes. But they are in series and you don't want to burn out any more filaments. So maybe from the 1800 ohm resistor side of the last 1lb4 to the 150kohm side of the first 1le3. That should be around 9 volts or so.

Maybe chime will 'chime' in with some other ideas.

When I was in tech school we had a fellow there who shorted out all the resistors on CB to increase the power. :eek:

So you may have quite a restoration ahead of you.

Yes to the variac. yes again to the 125 line voltage.I will start where you stated. I did notice That at least one of the heater lines did junction to a couple of caps parallel to a IF trans. I wonder if those mica or ceramic caps are bad.I will keep you posted. The 82 volts was across the "hot" cap. If I go from pos of the hot cap to chassis ground I had 5 volts " if " I remember. My printer is dead. I usually print the diagram and then write all over it. Now I keep running to the computer and then back to the set.Right now I am more worried about my radio.

Mica and ceramic caps are usually pretty stable. So I would not think that would be a problem.

You know I just realized those 1Lxx tubes all have a directly heated cathode. That might affect the voltage readings you are getting.

Which one is the hot cap?

And remember this circuit does not have a chassis ground.

Sure wish that schematic had some voltage readings.

Ok the deal with a directly heated cathode is the filament voltage is DC, and the signal voltage AC.

That would change the readings you get based on your meter settings and points you used as reference.

Sorry I missed that.

The cap that is getting hot is the 100mf @25 volts on the diagram. My set had a 200mf@25 in what looked to be an original sectional electrolytic.I went ahead and put in a 200mf cap.

I did replace the 100pf cap in the last tube in the series- heater line. I just did this because I had one. I put the tubes back in and tried the variac slowly keeping an eye on the voltage across the whole tube heater line. I reached 9 volts at about 90 volts on the power cord. This time I heard static out of the speaker. I also noticed if I tapped the chassis with a screwdriver the static stayed the same, but if I tapp any of the tubes besides the rect. the volume changed or the static changed. Looks like I need to clean some pins and sockets and try this again. Also in my area I can't pick up anything pretty much below 600kc. due to interference . This set also had the appropriate noise at this spot on the dial. no real stations came in though.

I feel the need to qualify an earlier statement of mine. I replaced a 100 pf. cap because it has full line voltage on it and it junctioned with the heater line(number 10 on the diagram by the junction were I was told to check voltage). it seemed the most logical to cause a back door problem being that the begining of the heater line is per the diagram. As I ran the set for a while I was able to turn up my variac and still maintain 1.5 volts across individual tube heaters. so, i am thinking that either the elctrolytics were still forming or I have a resistor changing value on me.I did not form the electros. because they are relatively lower voltages as compared to other AC sets.I did check B+ at 117v. so I now also need to make sure the voltage dial on my variac is accurate. I am thinking that the 117z6 should be putting out 117v. at the same line power.

Excellent progress! You have something coming out of the speakers and the filaments are not burning out. So you know you have B+, proper filament voltages and a working output stage.

That 100pf cap might well have been shorted. You can check them with an ohm meter by applying and reversing the leads. When you reverse the meter will deflect from the discharge. It's not a great test since it does not test the cap at working voltages Here is a link discussing capacitor testing

Your earlier problems might have been from the caps forming and resistors can change values. You can check them. It might be also that 125 volts just stresses the set too much.

On really old sets I just replace the electrolytics and the wax covered caps. Makes life easier.

As far as reception, if someone had been fiddling with the set all the transformer cores and trimmers in the IF and tuning might have been changed. :D

After dark you should be able to pickup stations across the country. But there could be alignment problems or some other cleaning issues in the tuning section. Typically alignment does not need more than a tweak if anything. But if someone was messing with the set who knows?

So the next question is do you have a signal generator?

Here is a link to an alignment guide for AA5 radios Yours is not an AA5 but and you have the procedure on the schematic (assuming you have rf generator). But he describes how to use a 2nd AM radio for alignment.

BTW WA2ISE posts here as well and has written some very interesting and informative articles online.

I have a cap checker(heathkit). I just have not used it . My signal gen. burned up but I have access to another so alignment will be easy enough. This radio came from Fair Radio in Lima, OH.They bought the stock from a tv/radio repair shop that closed in the 70's. I have purchased all sorts of radios and a couple tv's from them. What is unusual about the ones I have worked on is there are alot of mica/ceramic caps that are bad in these sets. The owner at Fair stated that he felt is was the fact that these sets were stored in an unkept building for 30 odd years. The temperature changes he felt ruined more caps then you would normally see. I did go ahead and spray this set with electronics cleaner last night but it is still kind of wet so I will try again later tonight.

Well, I retried my set and I am back to square one. Same problem again, blew my last 1lb4 output tube( too much heater voltage). The cleaner I used last night was an older slow dry type. I even took a hair dryer to it today to make sure it was ready to go.Well, I had bought the last 1lb4 tube that Fair Radio here in town had so I will try to go there and search the "back stock" to see if I can come up with another. In the meantime I am going to unsolder one end of every cap in the set and use my heathkit to see if maybe that cleaner although it was not the lubricating type, being it was slow drying did soak into a cap and short it out.The one thing I would really like to ask someone from Philco is why was this set not a "clean "series string as far as heaters went.Why all the side taps into B+ lines and junctions to IF secondaries?I was thinking that my overvolting issue was from a leaky cap tapped into a B+ line.I guess I will find out soon(not soon enough)!

Sorry to hear that. How did it go out? Was it operating for a wile? Is that cap still getting hot?

I was puzzled by the complexity of the heater string too until I realized it's a directly heated cathode. In other words the heater and the cathode is the same element. So you have both the heater and signal on the same element.

You might well be right about the caps shorting out either from cleaner or age. It's possible that they are good initially when you turn on the set but break down after being at working voltage.

If you can figure out what the filament resistance should be on the 1lb4, you could wire in a resistor of similar value as a dummy filament so you could trace out the problem with out burning out another 1lb4. On the other hand you might burn out something else.

How did it go out ? As soon as the rect. "hit". Yes the cap started getting hot again.It did not even hold long enough to get sound. Last night I left it running for 20-30 minutes before I turned it off and used cleaner.I did not think of cheating the filament line with dummies, I am going to try that, thanks.

You mentioned a resistor had been wired into the circuit but was on the topside of the chassis? And that the insulation was not well protected?

Maybe there are other 'presents' like that? Wires or solder connections close enough together that might cause an intermittent short if moved slightly?

I'm just guessing.

I would suggest replacing all of the electrolytics and wax coated caps. Add in the ceramic and mica's you are finding bad and that's just about all of them!

Don't suppose you could post some pictures?

I have done about 100 radios so far. I always replace wax and electro. caps first. Then check tubes and go from there.The resistor that I mentioned I already replaced under the chassis like it should have been(it was also the wrong resistance).I am going to recheck all solder connections for excess solder- shorts and any sort of self-inflicted stupidity. I do not have a digital camera yet. realistically I need one but I have other financial resposibilities ahead of it.

Sorry, i got the impression that the electrolytics were original. My mistake. That eliminates a lot of issues right there.

Understand the financial responsibilities side. All too well. I was just curious as to what it looked like under there.

It's a puzzlement for sure that it worked for 30 minutes last night but today POW. If I think of anything I'll let you know. Like I said yesterday it sure would be nice to have some voltage readings at certain points.

I would love to have a "sam's" with voltages all over it!!.
I am still wondering about the cleaner I used. I won't be able to tell for sure unless I cut open a mica cap and see cleaner dripping out of it but I can't help but think since that is the last thing I did that was the cause.

I'm not sure Sam's was around for 1941. In any event I have not been able to find one.

My thoughts are that since the radio failed the same way it did initially, the cleaner is less likely to be the culprit.

I found another link with 41-842 picture and schematic. No voltages but a parts list :)

http://www.geocities.com/jaschotter/philco41-843.html

(I'm uploading a bunch of files and it's going slow. So I'm trying to keep busy ;-))

I keep walking away from this set and then going back just in case I will notice something or think of something I haven't. Why does only one tube (1ln5) have a Floating isolated socket and what could happen if its mounts were crap and it touched the tuning cap? Would this be some sort of short? Because this is how it was when I flipped it over to put it away for right now.

Well look at the schematic. Both of the 1ln5s show a solid circle with a dashed circle inside. And one side of the filament is attached to the the case. I'm guessing these are metal tubes.

The socket is isolated for a reason. There are 2 - 1ln5s which one is isolated? That might be a clue.

On the schematic, is the 1ln5 between the IF transformers labeled 25 and 26 the one that is isolated? If that filament shorted it would directly affect the 1lb4 that is getting the high voltage on the filament.

It is the first IF amp, not the one you mentioned but I still will fix that. What is special about the diagram having the solid circle and then the dashes inside of that on the 1LN5 tubes?

Ok that was just a guess. And not a good one.

One side of the filament is connected to a shield (the inner dashed line on the schematic). Which I would guess is also attached to the metal band around the base and the pin?

Here is the tube data for that one:
http://www.bunkerofdoom.com/tubes/sy...949/1LN5_1.gif

Well, I checked with my ohmmeter and the floating socket will ground out the filament line if it touches anything.I will try to fix that and see what happens

I was able to find the 1LB4 tube I need so I will give it a shot as soon as I can.

I will be working overtime this week so I" may" not get back to this set until Friday night.

Cross your fingers!!

Fingers crossed. Best of luck and keep us posted.

Well,I found the time to rig the floating socket for now.

Now the tube heaters are not loading the circuit at all. they are not getting any juice.I will have to find the bad wire or open in the circuit and go from there.