Series cap exploded and kills other

[Ed_Chambley]

Question.  I put in series 2, 100uf/475v caps and 100k 3 watt resistors.  I know they were wired correctly.  The lamp limiter was dim.  In checking initial voltage 563vdc unloaded at the first set, choke to second series the same and voltage basically the same.  The cap held for about 3 or 4 minutes as I was wanting to get some initial readings.

Suddenly one of the caps exploded on the first node and of course the series one went as well.  I am trying to determine if I simply had a bad cap.  I moved the b+ to the choke feeding the second node of series caps and they are working fine.  Illinois caps.

Just checking to see if I need to limit the inrush in some way.  I have done this quite a few times but never had the problem.

[SILVERGUN]

Suddenly one of the caps exploded on the first node and of course the series one went as well.

Happy 4th of July Ed 

Illinois makes some nice firecrackers 

I don't have any words of wisdom for you other than, I have been using a Variac to slowly feed the caps at initial power up before I connect any other part of the circuit.....I like to see my power supply is alive and kicking before I move on....just a thought

Hope you had your safety glasses on 

[Ed_Chambley]

Suddenly one of the caps exploded on the first node and of course the series one went as well.

Happy 4th of July Ed 

Illinois makes some nice firecrackers 

I don't have any words of wisdom for you other than, I have been using a Variac to slowly feed the caps at initial power up before I connect any other part of the circuit.....I like to see my power supply is alive and kicking before I move on....just a thought

Hope you had your safety glasses on 

I had my glasses on, but it wasn't that bad.  It let go on the end and just spewed oil.  I did use a variac.  Always do.  In working on old radios, I have to reform caps all the time.  This is different and I am thinking I just had a bad part. 

I am wondering if I need to place a resistor across the DC switch.  This is why I am asking.  Funny thing is I was finished with what I wanted to check and felt confident the power supply was solid, then bam.

I have had amps I have repaired with a 470k resistor across the switch and the guy told me someone had put it there to slow the inrush.  I have never used one.  I just did the same thing to an old Sunn amp a few weeks ago and all went well.  This is why I thinking is was just a bad part.

Wouldn't be a bad idea to slow the inrush.  My problem now is I need a couple more caps, but thought I would ask about the inrush as well.

That was funny as hell, Happy fourth to you and I hope all your fireworks are intentional.

[eleventeen]

Funny post, Silver!!

I think you just had a bad part. Not much more to add to that assumption.

[stratele52]

If wiring are good and no reverse cap polarity, chance the  cap is defective . I don't use Illinois cap , they are low quality . But if the amp is a budget amp , why not.

I use always ( most of the time )  Safety Google when I work in a amp. You see why.....

[jojokeo]

In working on old radios, I have to reform caps all the time. 

I have had amps I have repaired with a 470k resistor across the switch and the guy told me someone had put it there to slow the inrush.  I have never used one.

Ed, I always use a 220k/1w or 2w resistor on my Standby switches and it doesn't cause any negative issue but has several positives.

I have a tube radio issue that I thought I'd run by you. After it turns on for a minute or two, the volume drops by about half and stays that way. I know it's not tubes so I was thinking the original filter cap would be the next logical replacement? But the radio is actually pretty quiet, any other suggestions?

[Ed_Chambley]

In working on old radios, I have to reform caps all the time. 

I have had amps I have repaired with a 470k resistor across the switch and the guy told me someone had put it there to slow the inrush.  I have never used one.

Ed, I always use a 220k/1w or 2w resistor on my Standby switches and it doesn't cause any negative issue but has several positives.

I have a tube radio issue that I thought I'd run by you. After it turns on for a minute or two, the volume drops by about half and stays that way. I know it's not tubes so I was thinking the original filter cap would be the next logical replacement? But the radio is actually pretty quiet, any other suggestions?

JOE, you know the deal.  How old is the radio?  Pre 60's I assume.  How often do you turn it on?  Does it have a rectifier tube?  If not, you should have replaced the selimun (sp?) with diodes.  Check voltages at turn on and see if they drop when volume drops.  If not, the field coil speaker check for rub.  Since most of us do not have field coil speakers just laying around to check.  If you decrease the volume know after the drop does it still work or is there a dead space where the pot makes no volume change until start getting to lower resistance on the pot.

How long after on does it start to lose volume?  After the temp is up?

To reform a cap can on an old radio, remove it and put it can side down in hot water for about 30 minutes.  Place a resistor 100k, 2 watt between the rectifier and first cap.  When you flip it on measure across the resistor and you should get 30 to 40 volts.  Leave it this way and check every hour until the voltage drops to less than 6 volts.
Your cap is now reformed and you did not even need a variac.  These are the 2 most common problems with radio beyond tubes.

Radio? Year?  How many total tubes?  For instance is it a 9 tube 1937 zeneth giant.

[jojokeo]

It's a "new" radio maybe from the 70's? Running one of those circuits made for 110volts or so w/out a mains transformer w/ a 35w4 rectifier and 50c4 output tube... and has two yes that's right TWO 4" dual speakers!!!  It's a GE from the day. I replaced all tubes and it still performs the same. A couple tubes that were suspect on my tester but the whole set cost like $12 or so, no big deal. I'd replace the two filter caps if I thought they'd make a difference but the radio is quiet on strong stations so the caps aren't the issue. When my finger gets close to the ferrite(?) tuning bar the sound/volume comes in much better. I don't know if this is related but I suspect not. Something gets a bit warm or whatever and the volume drops by about half. I can turn up the radio afterwards but it's just a little something that bugs me right now. Something is amiss and thought I'd throw it out there. The circuit looks to be very basic but there's no schematic inside.

[Ed_Chambley]

It's a "new" radio maybe from the 70's? Running one of those circuits made for 110volts or so w/out a mains transformer w/ a 35w4 rectifier and 50c4 output tube... and has two yes that's right TWO 4" dual speakers!!!  It's a GE from the day. I replaced all tubes and it still performs the same. A couple tubes that were suspect on my tester but the whole set cost like $12 or so, no big deal. I'd replace the two filter caps if I thought they'd make a difference but the radio is quiet on strong stations so the caps aren't the issue. When my finger gets close to the ferrite(?) tuning bar the sound/volume comes in much better. I don't know if this is related but I suspect not. Something gets a bit warm or whatever and the volume drops by about half. I can turn up the radio afterwards but it's just a little something that bugs me right now. Something is amiss and thought I'd throw it out there. The circuit looks to be very basic but there's no schematic inside.

Your hand is simply an antenna.  I assume you do not have an exterior AM Antenna, but wait this thing will do FM as well.  I forgot.  It sounds like a grounding problem is your voltage is cut in half.  Now, you will have to find the part that is causing it.  Check to see if the small chassis gives you any AC or DC reading to eliminate shorting.  No schematic, just follow the path of current taking readings.  First tho, make absolutely sure you are connected to an external antenna and are dialed into a strong station.  Radios get warm.  Is there any part other than tubes you cannot put you hand on and keep it there.  No hot parts, adjust the tuner.  Usually a flathead screwdriver slot on top of a rectangular post.

It is a little new for me, but the again it is just a radio and most of the time nowdays it is simply a weak transmission is you have no obvious part failure.  For example, my most sought after 12 tube Zeneth gets so hot that the top was checking when I got it.  I put in a heat shield.  Normal.  The little ones, like a bakelite silvertone I got a while back has the antenna made to the inside back.  Upon inspecting it I could see it was broken in a couple of places limiting reception.  I hooked it to an antenna and it worked very well.  AM only.  Repaired the internal antenna.  No volume drop until the station changes broadcast direction.

[jojokeo]

Thanks for the help Ed. What are the "tall" square aluminum things that are about the size of a tube but look like shielding, have a small pyramid shape, with a small hole on top? Their dimension is appx. 1 1/2" H x 3/4" W x 3/4" D

Maybe the pics will help show what a basic / simple radio this is?

[PRR]

http://www.wa2ise.com/

[Jack1962]

Illinois used to make some good caps back in the day , these you find today are use at your own risk.

[Ed_Chambley]

Thanks for the help Ed. What are the "tall" square aluminum things that are about the size of a tube but look like shielding, have a small pyramid shape, with a small hole on top? Their dimension is appx. 1 1/2" H x 3/4" W x 3/4" D

Maybe the pics will help show what a basic / simple radio this is?

If you are talking about the things with trimmers in top, they are transformers for the tube.  The trimmer adjust the tubes bias.  I cannot find a schematic based on the Model number.  Probably gonna need to find it.  I will look some as well.

[Ed_Chambley]

http://www.wa2ise.com/

Cool Site.  Thanks.

[jojokeo]

Ed, as I sit reading SG's recent exploits w/ the radio on the desk next to me, the vol goes up and down intermittently all of a sudden a few times. It usually starts out "normal" loudness and goes down and stays there. But now a few fluctuations. I'll have to open up the back and poke around I suppose? BTW, are those "transformers" supposed to be able to be wiggled as if a bit loose or is the aluminum housing just a shield for the internal tranny? I don't know anything about these.

[SILVERGUN]

Ed, as I sit reading SG's recent exploits w/ the radio on the desk next to me, the vol goes up and down intermittently all of a sudden a few times. It usually starts out "normal" loudness and goes down and stays there. But now a few fluctuations. I'll have to open up the back and poke around I suppose? BTW, are those "transformers" supposed to be able to be wiggled as if a bit loose or is the aluminum housing just a shield for the internal tranny? I don't know anything about these.

While your in there, why don't you install a PPICF 
Guaranteed to make it "better"
 

[Ed_Chambley]

Ed, as I sit reading SG's recent exploits w/ the radio on the desk next to me, the vol goes up and down intermittently all of a sudden a few times. It usually starts out "normal" loudness and goes down and stays there. But now a few fluctuations. I'll have to open up the back and poke around I suppose? BTW, are those "transformers" supposed to be able to be wiggled as if a bit loose or is the aluminum housing just a shield for the internal tranny? I don't know anything about these.

It is a shield.  When powered down carefully remove one and trace it.  You will know exactly what it does when you see it.  I feel confident.  It seems that you know it is acting differently than it was so something is wrong. Yes it is normal for the to wiggle, if you wiggle them.  If they are wiggling by themselves quit listening to Black Sabbath.  According to the tube, usually it directs the plate voltage through a trimmer back to the screen, that is if we are speaking about the same part.  How many tubes and are there 2 or 3 of the aluminum shields and does only 1 of the have a trimmer inside accessible from the top?  BTW, radio voltages are normally MUCH less than guitar amps. I have never seen much over 100 volts until the power section.

Jim Jenkins was the man's name who taught me about radio and TV. He did not call everything by the correct name.  They may not be called transformers, but they are coils just the same.  That is what he called them, so I call them the same. Just keep in mind you have a receiver and output as well.  Evidently you have become curious as that radio does not have a lot of value, but I get it.  I have a Channel Master (American company, but outsourced to Japan for a lot of assembly) 6534 I found in the North Carolina mountains.  When I found it it was worth maybe $10.  I gave $2 for it.  I did restore if, not my usual thing but it liked like it came from the jetsons.  We have a Mid century modern 50's room in our house, so I wanted it for the room.  It has become worth much more.  The reason I mention this one is it was having a similar problem.  It was simply a resistor.

As a matter of fact, all my radios have increased in value by more than 100% in the last 10 years.  There is a new demand for Cathedrals and the price is rising and I only have 1.

http://www.radiomuseum.org/r/channel_6534.html

There is a photo of the radio and a schematic. I am a member of the Radio Museum.  It could be very similar to the GE you have since the Japanese normally aren't innovators.  If you don't mind breaking some eggs, pull it apart and follow the path of the signal.  So many things can cause what you are describing, you will need to find where it fluctuates.  If you want to have a laugh, compare this schematic to an old 30's AM job and you will see why I look for the older radios.

[jojokeo]

  Good one SG! It's almost a toy circuit running on wall voltage like a bunch of Harmony's and others from the era.

I think I offered about $7 bucks and the guy accepted from an estate sale. The set of tubes were more. But it has my curiosity peaked. My very first amp I rebuilt was a similar wall voltage amp. It's what go me into wanting to learn about tube amp circuits in the first place even though I had a few Fenders and Marshalls when younger. Back then I didn't know anything about tube electronics.

[PRR]

> The trimmer adjust the tubes bias.

IF coil *tuning*.

All those coils need to be set the same, usually 445KHz? But do NOT tinker them! Old trimmers break. Trimming them needs experience and test gear (or lots of experience). They don't "go out" enough to matter.

Yes, the aluminum can is often loose. Not a problem.

Your problem is any wax cap, e-cap, other cap, or half-cent resistor.

It runs on 105V because that's CHEEP. No PT. The first "home loudspeaker radio" used a 400V tube to get a Whole Watt of output. Several generations of higher-current tubes allowed most-of-a-Watt with B+ derived withOUT a power transformer. And really, most AM fare in the home, you don't want a whole Watt. This is what everybody had 1950s-1960, and into the 1930s for folks without need for an impressive cabinet.

You don't need a right-model schematic. There's really only one way to do it. Different generations have different tube types, and different UL safety details. The power bottle may or may not have a cathode cap. The $12 model has a tone control. Some rigs run B+ _through_ the OT for a bit of hun nulling. Nothing major.

[Willabe]

If they are wiggling by themselves quit listening to Black Sabbath.

"Fairies wear boots and you gotta believe me. I saw it, I saw it, with my own two eyes."

 

When I was in high school, a sophomore, we went to see Black Sabbath at the old Chgo. Amphitheatre, by the old stock yards on the near south side, very bad neighbor hood, which was back then called the getto. It was bulldozed many years ago. We had what they called "box seats" which where just above the main floor and had little knee high walls around them about arm chair arm rest height with 4 seats in each. I think it held 20K to maybe 30K for a concert, saw Trower there that same year, great show. Well from what I remember any way.    

Where as the old Chgo. Stadium, which was also bulldozed, could hold up to 40K+? That's where the Bulls and Black Hawks play and where the Ringling Bros. and Barnum & Bailey Circus would give their shows when they came to town.

Anyway, were at the Sabbath show, sitting in the lower level box seats, so the bands playin, Ozzie's flashin the peace sign with both hands, wearin a tan fringed buck skin shirt, WOW! Way cool for a 16 year old, garage band guitar player who's smokin that funny stuff.

Next thing we know the Wonderful BS fans (yes I said "BS fans") above in the higher balconies started to light up cherry bombs and M80's and throw them down to where the other fans were sitting below.  

And like the Kool aid Man says, OH Yeah NOW we're having big fun!!!!!          Probable a few dozen went off during the course of the show and I'm ready to pee my pants the whole time as were my buddies.

After about 4, 5, 6 (?) went off in the Amphitheatre one went off in the box next to us, and as a good Chgo. boy who fooled with 4 of July fireworks you KNEW it was an M80, you could tell by the power of the blast being sooooo close, it was only about 15/20 minutes in and I feared for my life for the rest of the show. I kid you not!      

I've been to well over 100 big/er concert (10K+) shows from when I was 15 to say 24(?), let alone many smaller shows under 4K, 2K, 1K, .5K, and count less bars and have NEVER been afraid before or since for a reason like that!           

Now maybe you don't believe me?     Hmmm, because I didn't see fairies wearing boots? Ozzie must have had the "good stuff"?

        Now back to our regularly scheduled program.          
            


                       Brad        


(BTW, Series cap exploded and kills other, hey kinda fits, huh?)
 

          

[Ed_Chambley]

You don't need a right-model schematic. There's really only one way to do it

True, unless you get bit by the radio bug.  In buying Giant Consoles (I try to get only Zeneth) you may find (will find) a nice cabinet with a different chassis in it, or even converted to an amp.  Remembering that Radio was the form of home entertainment and the units were a considerable investment Pre WW2, they were repaired by anyone.  Lots of time by the owners.  My Grandfather told me about having to go outside and pour water over the battery so it would work again and live swapping of tubes to find one that worked from the boxes of tubes he and other neighbors had.  Yes, I am a Hillbilly.  Point being is they will be butchered.  Probably doesn't apply to a 60's mantle or table top, but I do have a bakelite silvertone someone gave me that they got at an Antique store.  A gift.  Someone had changed it dramatically.  I needed the schematic to put it back and come to find out the chassis had been changed.  Not uncommon.

These things were the central point of the home and usually considered by the woman of the home to be one of her prized decorations and you know what that means.  If the radio quits, the cabinet says, doilies and all.  The man of the house was expected to fix it.  Since rural areas are the only place you can get a good deal anymore it is imperative to have a schematic IF you intend for it to have value.  You can always do what some do on ebay and sell it as not working after you have gutted it for the necessary parts to restore one of value.  Someone will buy it.

There is really only one way to do it, but loads of variations of the one way.  It is very easy to repair radio, but I have never fooled with an old car radio and have wondered how a 6 volt car ran run a tube radio.

Strange how this topic has changed.

[sluckey]

have wondered how a 6 volt car ran run a tube radio.

They had an electro/mechanical vibrator with a bimetal set of contacts. 6V current was passed thru that bimetal strip and the contacts would open. Then as the bimetal strip cooled, the contacts would close again and the next cycle would begin. This action chopped the 6VDC into an ugly non symmetrical square wave at a frequency that you could often hear. The square wave fed a transformer to step up the square wave to be rectified for B+. Filaments were run straight from the battery. The vibrator was a very common failure item.

[PRR]

> unless you get bit by the radio bug.

Yup. However I thought the tube line-up here was a 35 then a 50C5 or equiv? That's the mature 5-tube "AC/DC" plan. Certainly 95% of all tube radios were this ilk. Yes, 90+% of those ended in the trash, a lower percent for the "nicer" high-price radios which were kept in hopes of eventual fix.
__________________________________________________

> current was passed thru that bimetal strip

Correct except for that bit. It's an iron clapper and an electromagnet that turns itself off. If you are old enough to remember alarm bells and buzzers (before piezo beepers), like that. With extra contacts.

The electromagnetic method gives hundreds of Hz. That bimetal thermal plan is more like a car turn signal, around 1 Hz. A 200Hz transformer is much smaller than a 1Hz transformer.

And, FWIW, VW ran radios with one power output transistor, all the tubes ran raw 6V on plates.

[sluckey]

The electromagnetic method gives hundreds of Hz. That bimetal thermal plan is more like a car turn signal, around 1 Hz. A 200Hz transformer is much smaller than a 1Hz transformer.

My memory on some of that old stuff I haven't worked on for 45 years is lacking. And I must be piecing together memories that don't belong together.    I was sure that I had seen the bimetal strip in one of those plugin cans, but you're right, it couldn't have been in that vibrator. Maybe I'm confusing with the old choppers on electric fence boxes. They had a similar plugin can that usually chopped about once every one or two seconds.

[PRR]

> electric fence boxes. They had a similar plugin can that usually chopped about once every one or two seconds.

AH! Yes, that makes perfect sense. You don't need steady high-volt, you do want long battery life. A ZAP every second or so will probably startle a cow or pig (or Corgi!) before they get through.

Electric fences were unknown where I was young. Here they are common, but of course today they are all transistorized, and I haven't had cause to open one up.