Emerson EC 425 went dead

9/10/2007 8:34:40 AMRon

I am a newbie at this so if the answer is obvious, I apologize. I recapped an Emerson EC 425 (schematic is on Nostalgia Air as EC) The person before me had replaced the electrolytics, there are two, the schematic calls for both of them to be 20 mf at 150 volts. The person before had replaced them with a 30 mf at 150v and a 30 mf at 450v. I assumed that he had used what he had so when I recapped the rest of the radio I replaced the electrolytics with 22 mf at 160v. When I turned on the radio it played well. I noticed that the volume control was touchy, it would cut in an out, but other than that it was picking up stations very well. After about 7 minutes, it went dead. Where should I begin my search for the problem? Was I incorrect in replacing the electrolytics according to the schematic? Thanks.

9/10/2007 10:39:54 AMBill J.

Ron,
Generally you can replace caps with a voltage rating equal to or higher than that specified - but you don't want to use a lower rating. Also swapping a 30MFD for a 20MFD usually isn't critical either.So, the previous repairer's fixes were probably okay. But, in searching for your problem now, start with simple first. First off, thoroughly check any repairs you have recently made and make sure they are wired properly compared to the schematic. Is it getting power? Is the power switch okay? Are the tubes lighting up? Even if they are, make sure and test them with a tube tester - you could still have a bad tube. You could also have a problem with your volume control. Test it with a meter to make sure it isn't open or intermittent. Test the obvious first (one thing at a time) before getting in deeper - many time it will save you a lot of time and misery.

9/10/2007 10:42:56 AMBill J.

:Ron,
:Generally you can replace caps with a voltage rating equal to or higher than that specified - but you don't want to use a lower rating. Also swapping a 30MFD for a 20MFD usually isn't critical either.So, the previous repairer's fixes were probably okay. But, in searching for your problem now, start with simple first. First off, thoroughly check any repairs you have recently made and make sure they are wired properly compared to the schematic. Is it getting power? Is the power switch okay? Are the tubes lighting up? Even if they are, make sure and test them with a tube tester - you could still have a bad tube. You could also have a problem with your volume control. Test it with a meter to make sure it isn't open or intermittent. Test the obvious first (one thing at a time) before getting in deeper - many time it will save you a lot of time and misery.

PS- make sure you have the polarity correct in caps you replaced.....

9/10/2007 11:36:43 AMron

::Ron,
::Generally you can replace caps with a voltage rating equal to or higher than that specified - but you don't want to use a lower rating. Also swapping a 30MFD for a 20MFD usually isn't critical either.So, the previous repairer's fixes were probably okay. But, in searching for your problem now, start with simple first. First off, thoroughly check any repairs you have recently made and make sure they are wired properly compared to the schematic. Is it getting power? Is the power switch okay? Are the tubes lighting up? Even if they are, make sure and test them with a tube tester - you could still have a bad tube. You could also have a problem with your volume control. Test it with a meter to make sure it isn't open or intermittent. Test the obvious first (one thing at a time) before getting in deeper - many time it will save you a lot of time and misery.
:
:PS- make sure you have the polarity correct in caps you replaced.....

9/10/2007 11:40:48 AMRon

When the radio went dead all the tubes went dark as well. I did check the on/off switch and it checked out ok. I will check the polarity of the electroylitics, but since it worked for a short time I was assumint that I got that correct (the last time that I switched the polarity I saw I wonderful display of smoke and the radio did not come on, since then I have tried to be careful :) ) Sounds like I should recheck the tubes, could they go out that fast on me? I replaced the 12sq7, but the rest checked out ok. Thanks for the help.

9/10/2007 12:52:12 PMBill J.

Per the schematic, your tube is an AC-DC set and tube filaments are in series - therefore if one filament burns out, the series circuit is broken and none of the other tubes will light up either. Retest your tubes with a good tube tester to check filaments and test for shorts, etc and check with a meter to make sure you are getting line voltage beyond the switch. I suspect you have a bad tube.

9/10/2007 2:07:08 PMRon

:Per the schematic, your tube is an AC-DC set and tube filaments are in series - therefore if one filament burns out, the series circuit is broken and none of the other tubes will light up either. Retest your tubes with a good tube tester to check filaments and test for shorts, etc and check with a meter to make sure you are getting line voltage beyond the switch. I suspect you have a bad tube.

Thanks, I will make some test tonight. Thanks again for the help

9/10/2007 2:15:08 PMLewis Linson

::Per the schematic, your tube is an AC-DC set and tube filaments are in series - therefore if one filament burns out, the series circuit is broken and none of the other tubes will light up either. Retest your tubes with a good tube tester to check filaments and test for shorts, etc and check with a meter to make sure you are getting line voltage beyond the switch. I suspect you have a bad tube.
:
:Thanks, I will make some test tonight. Thanks again for the help

An intermittent tube filament is not usual, but not unheard of either. I expect that is what you have. Either change tubes one at a time, or live dangerously and check for full line Voltage between filament pins when the string is open. Watch your fingers, 115-120 Volts going through filaments is still 115-120 Volts, and will bite!
Lewis

9/10/2007 7:14:51 PMThomas Dermody

Again, be sure that you connected the electrolytics properly. A backwards connected electrolytic can sometimes operate for a while, and then short out.

You say that you tested all of your tubes (since they are dark, a simple filament test is all you really need to do, since they seem to work well when they do light). You say that other than the 12SQ7, which I assume you replaced, they all checked out fine. Here's a problem that is often overlooked, though: The 35Z5 has a tapped filament. Often tube testers will connect pins 2 and 3 together, and the section of filament between those pins will go unchecked, and you will not notice if it is burned out. If your radio has a pilot lamp, this would be obviois, because the pilot lamp would get really bright, or would burn out. If the pilot lamp is burned out, you would never notice this. However, when the 35Z5 filament was good, it would have been stressed by the absence of a pilot lamp, which could have caused the failure. With the typical arrangement, B current also flows through the small section of the 35Z5 filament. A bad electrolytic (possibly caused by reverse polarity) could have blown the 35Z5.

Whatever the case may be, check the 35Z5 for filament continuity between pins 2 and 7, to be sure that both the sections between 2 and 3, and 3 and 7, are good. Also, if the radio uses a pilot lamp (#40 or #47, available at Radio Shack and any good hardware store), be sure to replace the pilot lamp. Finally, be absolutely sure that the electrolytics are installed properly.

Also, recently my very small Sentinel AC/DC set went out while it was running. It was due to a 12BA6 failure. The filament failed while the set was running. This is an uncommon thing (they usually fail at turn-on), but it does happen.

THomas

9/10/2007 7:50:29 PMRon

:Again, be sure that you connected the electrolytics properly. A backwards connected electrolytic can sometimes operate for a while, and then short out.
:
:You say that you tested all of your tubes (since they are dark, a simple filament test is all you really need to do, since they seem to work well when they do light). You say that other than the 12SQ7, which I assume you replaced, they all checked out fine. Here's a problem that is often overlooked, though: The 35Z5 has a tapped filament. Often tube testers will connect pins 2 and 3 together, and the section of filament between those pins will go unchecked, and you will not notice if it is burned out. If your radio has a pilot lamp, this would be obviois, because the pilot lamp would get really bright, or would burn out. If the pilot lamp is burned out, you would never notice this. However, when the 35Z5 filament was good, it would have been stressed by the absence of a pilot lamp, which could have caused the failure. With the typical arrangement, B current also flows through the small section of the 35Z5 filament. A bad electrolytic (possibly caused by reverse polarity) could have blown the 35Z5.
:
:Whatever the case may be, check the 35Z5 for filament continuity between pins 2 and 7, to be sure that both the sections between 2 and 3, and 3 and 7, are good. Also, if the radio uses a pilot lamp (#40 or #47, available at Radio Shack and any good hardware store), be sure to replace the pilot lamp. Finally, be absolutely sure that the electrolytics are installed properly.
:
:Also, recently my very small Sentinel AC/DC set went out while it was running. It was due to a 12BA6 failure. The filament failed while the set was running. This is an uncommon thing (they usually fail at turn-on), but it does happen.
:
:THomas

This is very helpful. When I first turned the set on I thought the pilot light was awfully bright, but just attributed to the fact that I had just put a new one in and I think it burned out. I will check the continuity as you suggest and double check the electrolytics. Thanks,

9/10/2007 8:48:23 PMRon

::Again, be sure that you connected the electrolytics properly. A backwards connected electrolytic can sometimes operate for a while, and then short out.
::
::You say that you tested all of your tubes (since they are dark, a simple filament test is all you really need to do, since they seem to work well when they do light). You say that other than the 12SQ7, which I assume you replaced, they all checked out fine. Here's a problem that is often overlooked, though: The 35Z5 has a tapped filament. Often tube testers will connect pins 2 and 3 together, and the section of filament between those pins will go unchecked, and you will not notice if it is burned out. If your radio has a pilot lamp, this would be obviois, because the pilot lamp would get really bright, or would burn out. If the pilot lamp is burned out, you would never notice this. However, when the 35Z5 filament was good, it would have been stressed by the absence of a pilot lamp, which could have caused the failure. With the typical arrangement, B current also flows through the small section of the 35Z5 filament. A bad electrolytic (possibly caused by reverse polarity) could have blown the 35Z5.
::
::Whatever the case may be, check the 35Z5 for filament continuity between pins 2 and 7, to be sure that both the sections between 2 and 3, and 3 and 7, are good. Also, if the radio uses a pilot lamp (#40 or #47, available at Radio Shack and any good hardware store), be sure to replace the pilot lamp. Finally, be absolutely sure that the electrolytics are installed properly.
::
::Also, recently my very small Sentinel AC/DC set went out while it was running. It was due to a 12BA6 failure. The filament failed while the set was running. This is an uncommon thing (they usually fail at turn-on), but it does happen.
::
::THomas
:
:This is very helpful. When I first turned the set on I thought the pilot light was awfully bright, but just attributed to the fact that I had just put a new one in and I think it burned out. I will check the continuity as you suggest and double check the electrolytics. Thanks,

Well, you nailed that one. I tested the 35z5 again and it tested fine. I then did the continuity test as you suggested and was open between 2 & 7 and 3 & 7. Interestingly enough a while ago when I ordered some tubes I went ahead and ordered a 35z5 to have on hand, it did the same thing. I then pulled a 35z5 out of another radio that I have yet to tackle and it's continuity tested as it should. I put it in the radio with a new pilot light and it lite right up and started picking up stations. I still have a problem with the volume control, it is loose and if you wiggle it the sound will clear up or produce a hum. Do I have to replace it or is there a way to clean them.
Thanks again for the help I am not sure how long this one would have taken me to figure out, if ever!

9/10/2007 10:11:00 PMLewis Linson

:::Also, recently my very small Sentinel AC/DC set went out while it was running. It was due to a 12BA6 failure. The filament failed while the set was running. This is an uncommon thing (they usually fail at turn-on), but it does happen.
:::
:::THomas

Commercial broadcasting stations have tubes that fail at turn-on, too. Do you know what it is like to sign off at midnight and have a 5:30 AM call for a &^%* tube filament that was working just fine five and a half hours ago when you turned it off and went home and to bed?

Lewis

PS About my house insurance...My company cut a check for the amount of storm damage that was not caused by the tree, and a few thousand for emergency repairs, which is supposed to be reimbursed by my neighbor's insurance company, and I return what I didn't have to spend to my insurance company, which I have done. The other insurance company is saying that accepting the check from my insurance company is saying that the damages have been covered, and they are through with us, while I sit here with a tarp covering half of my roof, while the insurance companies fight it out, relaying messages through me. I don't want anything I don't deserve, but dammit I want what is mine!
Oh, well, tomorrow is another day, and Georgia has a Great insurance commissioner's office.

Lewis

9/11/2007 12:23:10 PMThomas Dermody

Insurance companies suck. They are leaches.

Regarding the volume control, disassemble it and apply a thin layer of di-electric grease to the carbon track. If the track is worn heavily in certain places, move the wiper (if you can do this) so that it contacts a fresh area of carbon. The typical kind of potentiometer that's still used to this day has a configuration that allows this. Some early controls cannot be adjusted in this way. Make sure that when you adjust the wiper, it contacts the carbon on a rounded portion. If any sharp edges of the wiper contact the carbon, the carbon will be damaged.

Thomas

9/11/2007 4:18:52 PMRon

:Insurance companies suck. They are leaches.
:
:Regarding the volume control, disassemble it and apply a thin layer of di-electric grease to the carbon track. If the track is worn heavily in certain places, move the wiper (if you can do this) so that it contacts a fresh area of carbon. The typical kind of potentiometer that's still used to this day has a configuration that allows this. Some early controls cannot be adjusted in this way. Make sure that when you adjust the wiper, it contacts the carbon on a rounded portion. If any sharp edges of the wiper contact the carbon, the carbon will be damaged.
:
:Thomas

Thanks I will give it a try. Ron