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Replacing electrolytic cap with non-polarized a mistake with tube radio?

DickFreed

Aug 6, 2021
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Amongst the 3 other mistakes I’ve already made in trying to get an RCA Victor 4ra31 tube radio to work, I inadvertently replaced C12, the cap I have circled in schematic, with a non-polarized cap. It actually ran for a bit like this, but I ended up blowing the filament in the rectifying tube shown right beside of it. Was this perhaps why, or could I actually get away with this substitution?

https://imgur.com/a/6m2vUp8
 

crutschow

May 7, 2021
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If the non-polarized cap had the same capacitance and voltage rating as the original, then that should cause no problems, such as blowing the tube filament.
 

DickFreed

Aug 6, 2021
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Amongst the 3 other mistakes I’ve already made in trying to get an RCA Victor 4ra31 tube radio to work, I inadvertently replaced C12, the cap I have circled in schematic, with a non-polarized cap. It actually ran for a bit like this, but I ended up blowing the filament in the rectifying tube shown right beside of it. Was this perhaps why, or could I actually get away with this substitution?

https://imgur.com/a/6m2vUp8

edit: I can’t even seem to find a .047 electrolytic rated at 400 volts online to buy.
 

davenn

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Sep 5, 2009
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edit: I can’t even seem to find a .047 electrolytic rated at 400 volts online to buy.


The 0.047 is not and electro. it's a non-polarised cap .... not sure why you thought it was an electro ? ;)

One wonders if you have mistaken other non-polarised ones for electros ? :)
 
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DickFreed

Aug 6, 2021
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Yes one does. But first of all, I don’t know why I was pointing out C12 instead of C5. Especially since that it’s on opposite sides of the board. I hadn’t slept much the night before and had spent a large amount of time asking myself questions about this thing and not being able to figure out those questions myself.

C5 is the one I’m asking about right now. Not sure if I claimed the original to be electrolytic, but I did mean that I thought it was polarized. The fact it has a black band around the end and what looks to me as the symbol for a polarized cap as the pic below led me to believe this. So if not an electrolytic, is it not polarized as at least? Still looking for a definitive answer as to if I can use my non-polarized cap in it’s place.

https://imgur.com/a/2nZD0qj

here is entire schematic

https://imgur.com/a/GJzBpQo
 

Bluejets

Oct 5, 2014
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Yes one does. But first of all, I don’t know why I was pointing out C12 instead of C5. Especially since that it’s on opposite sides of the board. I hadn’t slept much the night before and had spent a large amount of time asking myself questions about this thing and not being able to figure out those questions myself.

C5 is the one I’m asking about right now. Not sure if I claimed the original to be electrolytic, but I did mean that I thought it was polarized. The fact it has a black band around the end and what looks to me as the symbol for a polarized cap as the pic below led me to believe this. So if not an electrolytic, is it not polarized as at least? Still looking for a definitive answer as to if I can use my non-polarized cap in it’s place.

https://imgur.com/a/2nZD0qj

here is entire schematic

https://imgur.com/a/GJzBpQo
Your full circuit is too small to make out anything.
Photo in #4 is a paper cap not electrolytic and reference to C5 in #6 is normal paper cap too I suspect as that is what the symbol shows.
There are many symbols used for electrolytics on the web so I suggest you familiarise yourself with them.
 

crutschow

May 7, 2021
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The fact it has a black band around the end and what looks to me as the symbol for a polarized cap
A black band around a non-polarized cap can indicate which wire is connected to the outside foil on a film capacitor.
This can be important to know when using the cap in high frequency circuits.
For example, if the capacitor were being used as a high frequency bypass to ground, you would typically connect the banded side to ground.
 

DickFreed

Aug 6, 2021
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A black band around a non-polarized cap can indicate which wire is connected to the outside foil on a film capacitor.
This can be important to know when using the cap in high frequency circuits.
For example, if the capacitor were being used as a high frequency bypass to ground, you would typically connect the banded side to ground.

Thanks. I’m still confused why I’m being told the symbol on the schematic does not indicate an electrolytic, or even polarized. Everything I’ve googled has indicated that |( is electrolytic. Unless my eyes need corrective surgery, that’s what is drawn for C5.
 

Ylli

Jun 19, 2018
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The only electrolytic / polarized capacitor in that circuit is C11 (A) and (B). Those old wax /paper caps quite often had a black band around one end but that was only to mark which lead was connected to the outside foil. The outside foil was usually connected to the lower impedance side of the circuit (where the cap is connected) to reduce hum pick up. Even though one of the leads was marked with that black band, the capacitor was not truly 'polarized' and would work installed either way.
 

ramussons

Jun 10, 2014
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Amongst the 3 other mistakes I’ve already made in trying to get an RCA Victor 4ra31 tube radio to work, I inadvertently replaced C12, the cap I have circled in schematic, with a non-polarized cap. It actually ran for a bit like this, but I ended up blowing the filament in the rectifying tube shown right beside of it. Was this perhaps why, or could I actually get away with this substitution?

https://imgur.com/a/6m2vUp8
Having seen quite a few valve radios in the old days, this schematic is a bit strange. The complete HV current flows through one half of the rectifier heater! Logically, it will mean that if there is any additional HV current (due to leaky capacitors or over driven tubes....), that section of the filament is likely to burn off.
I would suggest checking the filter capacitors C11A and C11B for leakage.
C12 is normally unpolarised and should not affect unless it is leaky.
 

Ylli

Jun 19, 2018
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Having seen quite a few valve radios in the old days, this schematic is a bit strange. The complete HV current flows through one half of the rectifier heater! Logically, it will mean that if there is any additional HV current (due to leaky capacitors or over driven tubes....), that section of the filament is likely to burn off.
I would suggest checking the filter capacitors C11A and C11B for leakage.
To say nothing about the turn on surge - surprised that filament section doesn't vaporize. Normally the whole filament is in the series string and a panel lamp is tied to between 4 & 6.
 

ramussons

Jun 10, 2014
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To say nothing about the turn on surge - surprised that filament section doesn't vaporize. Normally the whole filament is in the series string and a panel lamp is tied to between 4 & 6.
Equipment using vacuum tubes as rectifiers do not have a "surge" in the true sense since the heaters take time to warm up, which in turn limit the onrush current.
 

Ylli

Jun 19, 2018
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Equipment using vacuum tubes as rectifiers do not have a "surge" in the true sense since the heaters take time to warm up, which in turn limit the onrush current.
Good point, but I would still bet there is a bit of a surge as the rectifier filament starts to warm up and that 35W4 starts to conduct. But perhaps that is a 'feature' that reduces 'turn on' time.
 

DickFreed

Aug 6, 2021
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Having seen quite a few valve radios in the old days, this schematic is a bit strange. The complete HV current flows through one half of the rectifier heater! Logically, it will mean that if there is any additional HV current (due to leaky capacitors or over driven tubes....), that section of the filament is likely to burn off.
I would suggest checking the filter capacitors C11A and C11B for leakage.
C12 is normally unpolarised and should not affect unless it is leaky.

Thanks. I had already replaced those caps. Not sure how to check for leakage. I’ll have to look it up.
 

BFM

Jan 22, 2022
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Amongst the 3 other mistakes I’ve already made in trying to get an RCA Victor 4ra31 tube radio to work, I inadvertently replaced C12, the cap I have circled in schematic, with a non-polarized cap. It actually ran for a bit like this, but I ended up blowing the filament in the rectifying tube shown right beside of it. Was this perhaps why, or could I actually get away with this substitution?
https://imgur.com/a/6m2vUp8

I know this is an old post. If you are still trying to get this going, here is some advice. From what I can see of your schematic, you are working on an old AM radio. They were known as the "All American Five" as they have 5 tubes. Many companies made radios like these. They are extremely dangerous to work on as one of the two power cord wires is connected to the chassis. They used non-polarized plugs back then. If the plug is inserted into the wall outlet one way, the chassis will be at neutral. The other way and it will be live with 120VAC. If you touch the chassis when it's live, you could be electrocuted (death from electricity). You should always have an isolation transformer when working on equipment like this when it is powered on.

About the caps. Electrolytic caps on a schematic will show a "+" sign, (that is how you tell if it's an electrolytic) which designates where the positive end is attached to, like C118 is. Electrolytics usually have a higher capacitance rating, such as 1uf and higher. In a radio like that it is best to change all the electrolytics as they are only good for about 15 years or so. The non-polars will be any other cap in the radio. Many will be tubular and have a wax coating on them. Some may not have wax but have a plastic looking body. All of these tubular looking caps including the electrolytics are known as paper caps. They have paper inside instead of aluminium, foil or any of the other newer materials used today. They are dangerous to leave in as they are worn out and leaking DC through them.

A caps' number one function is to block DC from passing through it. DC passing through them causes hums, over voltages on tubes, and shorts. Also, the tubes as well as the resistors will need to be tested. You can test most resistors right in the radio with an ohm meter. Bad or out of tolerance resistors will cause many problems. They can be a little out of tolerance in tube devices, as the values don't need to be as critical as they need to be in solid state circuitry. New caps should not be leaking DC through them unless they are faulty, which is not likely or unless they were installed backwards.
 
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DickFreed

Aug 6, 2021
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Thanks for the clear explanation. I tested the tube and have replaced all capacitors. I will have to check the resistors as you say. I have an isolation transformer, but I believe it was falsely advertised as I have continuity from ground of the “isolated” side to the ground plug of my plug.
 

BFM

Jan 22, 2022
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Most are like that due to electrical codes. They can't have ungrounded sockets. When using one to just isolate the mains from your equipment for normal operation, as some do to cut down on interference from the mains, that's fine and that's how it should be. But for repairs and troubleshooting, you should open it up and disconnect the ground wire going to the output socket. The wire from the input and the output are usually connected together at the same point. Leave the input ground wire connected for protection, as the case is metal. If the device being tested has a two prong plug, then it's not a problem if the output socket is grounded. IF it's a three prong then it will be grounded of course and that is not good. You can use an adapter that the three prong can plug into, and the other end will have just two prongs. They used to be pretty common back when appliances started coming out with three prong plugs, and many houses still had only two prong sockets. Be careful about connecting coax, ground clips from test equipment and other wires that go to ground to the unit being tested as they will ground it, and you could get a shock. There are very good videos a fellow has on electronics and repair of many different radios and other equipment. He goes through the whole troubleshooting process, repair, alignments and explains everything. With my 52 years in the electronics industry, I even learn a few things from him sometimes. He's at https://www.youtube.com/user/MrCarlsonsLab/videos and for $2 a month you can join him on Patreon where he has about 136 videos teaching electronics and repair. Good luck. I'm sure you will get it going.
 
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Martaine2005

May 12, 2015
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I agree with @BFM.
Mr Carlsons Lab is a great channel.
You could also add a switch on the unit for floating and grounded.
upload_2022-1-23_20-46-42.jpeg
 

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