My new project

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Re: My new project

Post by Dr. Radio on Sun Dec 14, 2014 12:07 pm

frank1956 wrote:
                                                                                                                                                                                I took  my analog  meter an shorted it out by touching  the two probes together . I set it to 10X and proceeded  with the first test the needle  did move but not to zero  but rather to 10 on the meter scale. Since you stated a short was zero and I did not get that I  wanted to see where  I stood before moving  on to the next phase .

Frank

Good Morning Frank,

Good question.

Analog meters have a "zero adjust" wheel or knob to set the movement of the needle to "zero" on the scale when you short the test probes together. This is to compensate for battery strength, resistance in the test probes themselves and the circuitry in the meter.

You need to "zero" adjust each time you set the meter to a different resistance scale (X1 X10, X100 etc) and each time you turn the meter on from rest.

Once you set it, leave it alone for the period of time you are running your tests.

FYI, leaving the knob in one of the resistance scales when you are not using the meter can prematurely run down the batteries.
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Re: My new project

Post by Dr. Radio on Sun Dec 14, 2014 12:09 pm

So.....short the probes together, adjust the meter so it reads zero ohms and proceed with the tests.
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Re: My new project

Post by 75X11 on Sun Dec 14, 2014 1:19 pm

Yes.
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Re: My new project

Post by frank1956 on Sun Dec 14, 2014 1:29 pm

Dr Radio ,
Good Afternoon. I believe  you  misinterpret  my post . Idid zero  out my meter before conducting  the first test. My reading on the meter scale was 10 when I did the first test and not zero which if I understand correctly means a short. My question is since it did not go all the way across the scale to zero , but did move  to 10 with the meter set to 10X  do I stop or proceeded with the next phase ?

Frank
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Re: My new project

Post by Dr. Radio on Sun Dec 14, 2014 2:07 pm

Oh. I see.

Frank, if the first indicated "10", this means 10 X 10 or 100 ohms across the switch contacts. This is very high resistance where it should only be a few ohms AT MOST.

This tells me the switch portion has gone bad. The tiny contacts didn't fare so well with a direct short when the radio was turned on.

What you need to do at this point is solder in a jumper wire across the switch lugs, effectively shorting across the switch. The radio will be "permanently" on for the time being.

Once you're done "jumping" the switch, proceed with the tests.

If you still don't have zero ohms in the first test with the jury rigged switch, then there are other issues. If it is okay, proceed with the other steps until you have a question or run into more trouble. Smile
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Re: My new project

Post by frank1956 on Sun Dec 14, 2014 3:29 pm

This jumper wire will go between where the power cord goes (B+) and the B- go on the volume control ?

If this ls the case I will at some point have to get a new volume control switch ?

Frank
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Re: My new project

Post by Dr. Radio on Sun Dec 14, 2014 4:20 pm

The "B+ " is totally different then the incoming power cord.

But I think you have the idea. There are (2) lugs on the BACK of the volume control. These are your switch connections. Solder a piece of wire between these so the switch is always on. Do it right there at the switch. Don't connect anything to B+ or the three lugs that represent the volume control lugs on the switch.

One step at a time, don't worry about what parts you may or may not need.
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Re: My new project

Post by frank1956 on Sun Dec 14, 2014 6:38 pm

Dr Radio ,
Here is my progress .

(1) Jumper wire done I have achieved zero ohms .
(2) Went to step 2 . Checked pin's 3 & 4 of each tube . Started with  12AT6 and ending with 35W4 Needle moved on each tube . Only one pegged to zero ohms and that was pin 4 12AT6 . Don't sound good since zero ohms is a short correct ?

Frank
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Re: My new project

Post by Bill Cahill on Mon Dec 15, 2014 11:20 am

No.

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Re: My new project

Post by Dr. Radio on Mon Dec 15, 2014 9:18 pm

frank1956 wrote:Dr Radio ,
Here is my progress .

(1) Jumper wire done I have achieved zero ohms .
(2) Went to step 2 . Checked pin's 3 & 4 of each tube . Started with  12AT6 and ending with 35W4 Needle moved on each tube . Only one pegged to zero ohms and that was pin 4 12AT6 . Don't sound good since zero ohms is a short correct ?

Frank

Frank,

There's an easy way to tell whether or not there is a direct short across the 12AT6 heater connections at the tube socket OR you are simply reading the low resistance thru the actual heater inside the tube.....

What do you think that is?

(Yes, I'm quizzing you to help hone your troubleshooting skills and circuit logic). Smile

Let us know what you think, then one of us will reveal the answer.

I'm serious, not being a smart@$$.
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Re: My new project

Post by frank1956 on Tue Dec 16, 2014 10:38 am

Dr Radio ,

It would be the low resistance across the tube . The way I got this was to pull the tube and take the reading across pin's 3 & 4 which showed zero ohms .

I also took the same reading across pin's 3 & 4 on the tube sockets minus the tube and got a reading on pin 3 and not pin 4 .

So which means there is no short in the radio , but rather the tube  ?

Frank
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Re: My new project

Post by jerryhawthorne on Tue Dec 16, 2014 2:19 pm

Frank, could you please expand on the quote? If you measured from pin 3 to pin 4 how you determined you got a reading on 3 and not 4?
"I also took the same reading across pin's 3 & 4 on the tube sockets minus the tube and got a reading on pin 3 and not pin 4 ."
Were you measuring from socket pin to B-? ie: Pin 4 to B- and then pin 3 to B-? With the tube out that would make sense.
Jerry

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Re: My new project

Post by Bill Cahill on Tue Dec 16, 2014 2:37 pm

All we are trying to determine is whether, or, not, a tube is burned out. Put all the tubes back in their sockets, and, leave them in while you check across pins 3, and, 4 of each tube socket. Do not remove any of the tubes for this test. Your needle on your analog meter should show a swing, and, resistance for all tubes. If the meter doesn't move for one of the tubes that tube is burned out, and, has to be replaced....

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Re: My new project

Post by frank1956 on Tue Dec 16, 2014 4:37 pm

Dr. Radio wrote:
frank1956 wrote:Dr Radio ,
Here is my progress .

(1) Jumper wire done I have achieved zero ohms .
(2) Went to step 2 . Checked pin's 3 & 4 of each tube . Started with  12AT6 and ending with 35W4 Needle moved on each tube . Only one pegged to zero ohms and that was pin 4 12AT6 . Don't sound good since zero ohms is a short correct ?

Frank

Frank,

There's an easy way to tell whether or not there is a direct short across the 12AT6 heater connections at the tube socket OR you are simply reading the low resistance thru the actual heater inside the tube.....

What do you think that is?

(Yes, I'm quizzing you to help hone your troubleshooting skills and circuit logic). Smile

Let us know what you think, then one of us will reveal the answer.

I'm serious, not being a smart@$$.





Jerry ,Bill,

Was answering Dr Radio question .
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Re: My new project

Post by frank1956 on Tue Dec 16, 2014 4:46 pm

Everyone have a Merry Christmas aan a Happy New Year. Will be out of pocket for a couple of weeks starting Thursday until the 1st of the year . Very limitd internet access .

Jerry to answer your question when I was reading across pin's 3 & 4 on the tube sockets minus the tube i was reading the pin and B-. Hope that makes sense .


Frank
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Re: My new project

Post by Bill Cahill on Tue Dec 16, 2014 11:10 pm

No it doesn't. That's not what I wanted you to do.....

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Re: My new project

Post by Wildcat445 on Tue Dec 16, 2014 11:13 pm

Merry Christmas from The Valley Of The Sun, Frank!

WC

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Re: My new project

Post by frank1956 on Fri Dec 19, 2014 10:25 am

Dr Radio ,

So is my answer correct ?

Or did I miss the whole point ?

Bill ,
The test you are asking about was done several threads back .

Frank
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Re: My new project

Post by Bill Cahill on Fri Dec 19, 2014 11:55 am

Please explain. I only remember you doing the test with the tubes out of their sockets. And, there is some doubt, yet, of the condition of your meter.
Put your ohm meter leads together. the needle should show swing, and, a dead short.
If not, your meter is in doubt.

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Re: My new project

Post by frank1956 on Fri Dec 19, 2014 1:44 pm

Bill ,

Please read page 14 middle ways down , this was done with tubes in the tube sockets and with the radio on. Meter was zero out each time . Meter works fine .

Analog meter was used for this test . I was responding to Dr Radio question right below that .

Frank
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Re: My new project

Post by Dr. Radio on Fri Dec 19, 2014 9:36 pm

Hi Frank, Happy Holidays to you and yours. Not sure if you'll read this, but to summarize.....


First off Bill, we have determined his meter and his use of the meter are correct.

With the utmost respect to the others, I must say the method I provided Frank to follow does a much more thorough job of testing the series string heater circuit. Just testing 3 and 4 (at the tube socket connections), doesn't tell us a whole lot--specifically, that methodology would not have caught the bad on/off switch so quickly. Another real life scenario is there could be a solder "tail" or excess wire, mis-wire etc. that causes a short between #3 and #4 terminal lugs. That would "test" great, but in reality prevent the radio from working.

That's why I quizzed Frank. Yes, Frank, by removing the tube and the "short" going away, this automatically indicates the wiring and tube socket are not at fault.

Frank, if you follow my method, there is NO reason to go back and check both pin 3 and pin 4 on each socket. With each move of the test probe to each pin 4, you would see a problem with the previous pin 3 if there was one. A break in a previous connection would become obvious is this is just a simple series circuit.

Now, is the tube truly "at fault"? Is it truly reading ZERO ohms, a dead short? That is the question at hand

A typical 12AT6 should read about 10 ohms "cold". Meaning, you pick a 12AT6 tube out of a pile of tubes and touch your meter probes to pin 3 and 4 (with the tube laying on the table), you should see roughly 10 ohms or so with the meter on the X1 position. On the X10 position, it should swing almost to ZERO, or a short, but not quite. All depends on the meter. If the tube causes the meter needle to PEG ZERO (or dead short) on X1, then the tube has an issue.

By far the simple method, is to pop another 12AT6 tube into the radio and see if the results are the same.

To be honest, you're getting pretty darn close to firing up this radio based on what you're reporting. Please don't though until any questions on the basics of the heater power supply are cleared up. There are also some power safety thing to review as well.

Not sure if you'll be reading this on your Holiday Break, but again, Happy Holidays to You and Yours and everyone here on TRF

Smile
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Re: My new project

Post by Bill Cahill on Fri Dec 19, 2014 10:28 pm

I'm bowing out. Apparently, my help isn't doing much good. Good luck.

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Re: My new project

Post by jerryhawthorne on Fri Dec 19, 2014 11:18 pm

Bill, I'm with you, Doc is doing a great job with a lot of patience. Frank is learning. If this ever, well when the radio is up and running it is time to open a bottle and celebrate! I'm back to just watching! Something like this just needs a single mentor as we all have different ways of approaching problems and it gets confusing to the poor Frank. Happy holidays to all from our condo in So. Ca.
Jerry

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Re: My new project

Post by frank1956 on Sun Dec 28, 2014 7:41 pm

Hope everyone had a Merry Christmas. I should be back on board with this project by next Monday the 5th of January 2015, ready to get back in the saddle.

Wishing everyone a Happy 2015 New Year.

Frank
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Re: My new project

Post by Dr. Radio on Mon Dec 29, 2014 11:14 pm

Happy New Year Frank.

Be patient, about the time you're back, I've got some training/certification things going on at work, so I might not be able to respond too quickly (as usual Smile ), but there is always plent of help here.
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Re: My new project

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