cap's change

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cap's change

Post by bennie hall on Tue Jul 23, 2013 3:28 pm

Hi as some one told me the other day i need to go back and study more on tube radios and stopfor now. ma- bey he was right i was going along great changing cap's after each change i would turn the radio on and i would have great sound then i changed one and noise with a little sound.so i tried all the other caps i had left and even used jumpers on the old cap but no help.LOST FOR NOW. Bennie

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Re: cap's change

Post by Wildcat445 on Tue Jul 23, 2013 7:00 pm

What are you doing, Bennie? Are you still working on the Arvin? It would be easier to help you and to follow your project more closely if you would only post one thread about this project. Multiple threads cause me, at least, to have to do WAAAAYYYY too much thinking and reading to be able to post an intellingent suggestion or response. Do not feel bad about getting stuck. You are learing a little each day. That's how we all did it and the only way you can do it. We are happy to help. The comment about your needing a tad more instruction on radio repair is a reflection on a fact you likely already knew. There was no disrespect intended, I'm sure. Hang in there, Bennie. There are good texts available on radio repair. I will send you a PM with some suggestions.

There are a couple of prevailing practices on changing capacitors. One method, and the one I use, is commonly referred to as "shotgunning." Replacing all the capacitors at one time, many times without even trying the radio to see if it worked before the caps were changed. The reason I do it this way is that if you are trying to fix a radio with old, leaky caps, you may chase your tail trying to find a problem that new caps would have fixed. I find it better to have to diagnose and repair a fault after the caps are known good.

The other practice is to change caps one at a time and note if you introduced a new fault. I find this method far too labor intensive for my taste. I am not recommending either method. You need to use the method that suits you best and one that you can follow and feel good about. In my opinion, neither method is right or wrong. Just a different way of accomplihsing the same task. Fixing the radio. Good luck, Bennie. You will get there. Trust me. Never give up or let 'em see you sweat!

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WC




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Re: cap's change

Post by bennie hall on Tue Jul 23, 2013 10:20 pm

Thanks WC i am just new at this and i know it.but i am not sweating just frustrated at my lack of knowledge but i'll get there.and to clear up so post i have made no i am not working on the Arvin all i did with it was change the power cord and it was dead.so i started on my radiola 61-5 i ordered new cap's.and started replacing them one at a time.each time trying the radio and it went great for about 5 cap's and then a lot of humming with just a little music in the background.so i tried the old cap with test clips no good then.i tried all my cap's and no change.so now you know the (PAUL HARVEY)rest of the story.thanks for looking over my shoulder.Bennie

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Re: cap's change

Post by Wildcat445 on Wed Jul 24, 2013 7:01 pm

I would like to help you develop a disciplined diagnostic procedure to use when you work on a radio. Failure to develop such a procedure will only increase your chances of failure and guarantee certain frustration. Each person has his own procedure for checking out, troubleshooting and repairing a radio. Whatever works for you is the correct way. You will develop your method with time. So, for sake of trying to help you get a handle on radio repair, I will share my basic procedure with you. Another point that should be mentioned here is that we are always glad to offer whatever assistance we can to help you. It is common courtesy to not only acknowledge those suggestions, but to actually try them and then get back with the results. When someone tries to help and his suggestions are ignored, future suggestions sometimes come less frequently.

The first thing I do when I get a radio home is to put it out on the deck of my shop, remove the chassis and blow the chassis and cabinet out, GENTLY, with compressed air. This removes not only the dust and dirt, but also removes any critters, alive or dead, that may have taken up residence in there. Then I pull up and print out the service information for the radio. This will give me a parts list with component values, voltage and resistance measurements, alignment instructions, and a schematic, the road map of a radio electronically. I look the schematic over and note any circuit design that I may not be familiar with, tube complement, etc. Then I pull a set of spare tubes to have on the bench should they be needed.

Next, I place the chassis on my service bench and secure it so that I can make repairs and tests without the chassis falling or being unstable. On small AA5 chassis, I merely clamp the edge of the metal chassis to my bench with Vise Grips. Larger chassis are put on my "rotisserie" that allows me to turn the chassis in different ways in order to more conveniently work on it. I check the power cord visually and with my ohmmeter. Then I turn my attention to the primary of the power transformer and the power switch. If those components check out, I pull the rectifier and plug the chassis into my isolation transformer/Vairac/dum bulb tester and slowly power up the transformer. I start at about 60 volts for about 2 minutes then increase in 10 volt increments for two minutes each until I reach full line voltage. At each step, I look for the bulb in the dim bulb tester to indicate a short, for smoke, listen for frying or noise, and see if the other tube filaments and the dial bulbs light. My reasoning for checking the power transformer first is that if this transformer is dead, no amount of other work on this radio will make it play with a dead power transformer! If all is well, I remove power and perform resistance checks on all the antenna coils, oscillator coils, IF transformers, interstage coupling transformer, output transformer, field coil and speaker voice coil. I clean all the contols and resistance check the tuning capacitor to make sure it does not have a short. I test all the tubes on the tube checker. If everything checks out okay this far, I figure that my odds of having a working radio when I am done are in my favor.

Next, I replace all the aging components known to fail. I replace the filter capacitors, paper coupling capacitors, check resistors, and I personally replace any that are more than 10% out of spec. I replace the dial bulbs, any wiring necessary, the power cord unless it is extremely nice. I shotgun my caps, since I find that easier for me. Either way is fine, whatever you are most comfortable with. I use a highlighter to mark on the schematic as each component is checked or replaced. I make notes on the back of the schematic of anything I see that may need further attention. This helps me eliminate errors caused by faulty memory. I also have a service library of 3x5 cards with each radio, the model number and manufacturer, tube complement, number of bands and what I did to make the set work on this card. I can then reference this card, should the radio fail at a future time, and I want to know what was done. After I get everything done, I recheck my work, and clean up anything that is not done as well as I can do it.

I should have a working radio. Again, I plug the set into my iso/variac/dim bulb tester and ramp up the voltage slowly. In increments much like when I did on initial testing, only this time with the rectifier in place. I put three meters on the chassis to monitor voltages. A VTVM measuring B+ at the rectifier cathode, a VTVM measuring B+ at the input filter capacitor, a VTVM measuring B+ at the plate of the output tube. Call me paranoid, this covers my butt if I have done something wrong. By bench power source is fused, the iso/variac is fused, and I usually install a fuse in every set with a power transformer. Again, I look for the magic smoke, or anything that appears amiss. By the time I reach full line voltage, and nothing has smoked, I should be hearing a working radio. It may need the alignment touched up and a few little odds and ends mopped up, but this should give me positive results.

Let's assume for a second that the radio still does not work. Now I would reference the schematic and start making voltage measurements to determine where the fault lies. I isolate the radio, stage by stage. I usually start at the speaker and work toward the antenna. I place my finger or the tip of my plugged-in soldering iron on the center terminal of the volume control. A loud buzz indicates that the power supply and the audio stages are working. I would then troubleshoot the front end of the set from the volume control to the antenna. No buzz would indicate a problem with the audio section or the power supply. This scenario is unlikely, since I just performed all these tests, either before or during the restoration.

Hopefully, this brief overview will give you some idea of how to work on a radio, successfully, and minimize chasing your tail and getting frustrated. Frustration is not sin. Just back away for a bit, collect your thoughts and then forge ahead. I am sure others will chime in with other good ideas that will help you. Hang in there, and good luck.

Regrds

WC




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Re: cap's change

Post by Resistance is Futile on Wed Jul 24, 2013 10:53 pm

bennie hall wrote:Thanks WC i am just new at this and i know it.but i am not sweating just frustrated at my lack of knowledge but i'll get there.and to clear up so post i have made no i am not working on the Arvin all i did with it was change the power cord and it was dead.so i started on my radiola 61-5 i ordered new cap's.and started replacing them one at a time.each time trying the radio and it went great for about 5 cap's and then a lot of humming with just a little music in the background.so i tried the old cap with test clips no good then.i tried all my cap's and no change.so now you know the (PAUL HARVEY)rest of the story.thanks for looking over my shoulder.Bennie  


You could have a bad cap!
The 5th cap is suspect, you can always get the polarity backward and may need reversal I could be wrong, or,or,or it may be connected to the wrong point. Since you get weak music it sounds like the right direction to go in. Also if you have inherently disconnect a grid wire connection, whilst puttering with the wiring you could have a loud hum. Or if the caps are all good then you may have a tube that couldn't handle to corrected voltage and has shorted out the cathode to heater in one of the tubes.

Another issue may be wiring that is to close to the heater power to filaments probably the volume control or if not then grid wires. (sometimes components get replaced and wires are not dressed correctly to original layout. Hope this helps.

You really need to get a book on radio troubleshooting methods and read it cover to cover, Then if you don't understand a books comments on an issue, ask us for clarification. We do have some good troubleshooters, but you must be systematic in your repairs as was stated.
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vacation

Post by bennie hall on Fri Jul 26, 2013 1:34 pm

Hi guys thank's for all your help on my first try with old radios.going to take a few days off and go to the beach with family and cool my head.so i'll talk at you later.Bennie

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Re: cap's change

Post by 75X11 on Fri Jul 26, 2013 4:35 pm

That's maintaining your most important tool! All of us take a break regularly. Sometimes you can solve some of the problems in your mind before going back to the workbench.
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