My new project

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Re: My new project

Post by frank1956 on Sun Nov 30, 2014 11:18 am

75,
Thanks.
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Re: My new project

Post by Dr. Radio on Sun Nov 30, 2014 12:12 pm

So Frank, are you NOT using an isolation transformer to power your radio?

That is quite dangerous with an AC/DC radio.

Halfway thru this page: http://www.tuberadioforum.com/t1915p45-step-by-step-restoration-ge-t-106c-let-s-go-for-it


If you weren't using any isolation, that is where the additional capacitor on the ground lead of the signal generator would come into play so there isn't a direct high voltage short between the radio B- and the signal generator cable ground.

The ground cap is meant to protect the equipment, but you should be using an isolation transformer which protects the human working on the radio!

Please clarify how you are set-up and exactly how things were connected.
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Re: My new project

Post by Bill Cahill on Sun Nov 30, 2014 5:50 pm

Along with probably damaging a resistor, you likely burned out the filament on one of the tubes. Probably the rectifier.
Replace those damaged parts, and, the radio should come back to life.

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Re: My new project

Post by frank1956 on Sun Nov 30, 2014 7:36 pm

Dr. Radio wrote:So Frank, are you NOT using an isolation transformer to power your radio?

That is quite dangerous with an AC/DC radio.

Halfway thru this page: http://www.tuberadioforum.com/t1915p45-step-by-step-restoration-ge-t-106c-let-s-go-for-it


If you weren't using any isolation, that is where the additional capacitor on the ground lead of the signal generator would come into play so there isn't a direct high voltage short between the radio B- and the signal generator cable ground.

The ground cap is meant to protect the equipment, but you should be using an isolation transformer which protects the human working on the radio!

Please clarify how you are set-up and exactly how things were connected.

Dr. Radio,
I connected a .1 @ 630 volt cap from the HOT lead of the signal generator to another alligator clip via the #1 pin of the 12BA6 tube and then connected the ground to the #2 pin (B-). Again the alligator clips made contact and cause the sparks and smoke.

Frank
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Re: My new project

Post by Dr. Radio on Sun Nov 30, 2014 9:22 pm

Frank,

I understand that, but you still didn't answer my question. Are you just plugging the radio directly into the wall outlet? Or are you using an isolation transformer to power the radio?

The reason I'm asking is, 1) this is an important safety concern 2) this will assess what really happened.

You shouldn't have had such a violent spark even if pins 1 and 2 were shorted on the 12BA6 tube. Now, having an un-isolated radio set-up being connected to signal generator, then I can see issues.

Let us know. Also, in the mean time, you can test the tubes. No lighting, means open heater(s). The 35W4 for example, acts like a fuse when there is a heavy B+ draw/short. I could see that possibly going poof. Any of the tubes could have open heaters at this point.

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Re: My new project

Post by frank1956 on Sun Nov 30, 2014 10:50 pm

Dr. Radio,
To answer your question yes I have been just plugging the radio into my wall outlet at home.The old plug on the radio was changed out to a modern polarized plug.

I am not sure what you mean by having an un-isolated radio set-up being connected to a signal generator, I have used the setup I explained early, by connect a .1 capacitor @ 630 volts to HOT lead of the signal generator to do all my alignments.

Frank
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Re: My new project

Post by frank1956 on Mon Dec 01, 2014 9:43 am

Dr. Radio wrote:Frank,

I understand that, but you still didn't answer my question. Are you just plugging the radio directly into the wall outlet? Or are you using an isolation transformer to power the radio?

The reason I'm asking is, 1) this is an important safety concern 2) this will assess what really happened.

You shouldn't have had such a violent spark even if pins 1 and 2 were shorted on the 12BA6 tube. Now, having an un-isolated radio set-up being connected to signal generator, then I can see issues.

Let us know. Also, in the mean time, you can test the tubes. No lighting, means open heater(s). The 35W4 for example, acts like a fuse when there is a heavy B+ draw/short. I could see that possibly going poof. Any of the tubes could have open heaters at this point.


Dr.Radio,
I replaced all the tubes with tested working tubes and still no life??

Frank
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My new project

Post by Bill Cahill on Mon Dec 01, 2014 12:07 pm

You may have burned out the isolation resistor on the 35W4.

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Re: My new project

Post by frank1956 on Mon Dec 01, 2014 1:53 pm

Thanks Bill. Since I only see one resistor on the 35W4 I assume it is the 1200 ohms resistor you are talking about?

Frank
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Re: My new project

Post by Dr. Radio on Mon Dec 01, 2014 9:56 pm

Frank,

A "dead" radio is easiest to troubleshoot. Get out the ohm meter and see where the circuit is broken. No tube lighting means there is an open in the heater circuit. All the tubes' heaters are in series like Xmas lights.

Now, before you go forward, you need to get an isolation transformer. Equipment damage is one thing, in which you just may have found out, but the bigger issue is your health and well being. Simply plugging in your radio into the wall outlet is one of the most dangerous things you can do. An AC/DC set is a transformerless design. One side of the power line is coupled to the chassis and one side is directly connected into circuitry. It doesn't matter you put a new plug on it. When you connect other equipment to it, you risk a high voltage short. The capacitor on the "hot" or high side of the generator provides no protection when the low or ground side of your generator may very well be going to "opposite" 120 volt circuit connection on the wall outlet. Old schematics indicated putting a cap in series with the low side so as when it is connected to the chassis or B-, you don't have a direct short, but you still have current flow. Capacitors pass AC. There is simply no substitution for an isolation transformer and no substitution for safety.

If you want to continue with this radio or other AC/DC radios, you need that isolation transformer.


That's why I made a point to mention this in page 4 of this thread and did quite a write up on the link I provided in my restoration thread.

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Re: My new project

Post by frank1956 on Tue Dec 02, 2014 10:28 am

Dr. Radio,
Thanks for the safety tip. I may or may not have what I need, what is the difference between an isolation transformer and a variable voltage control??

But on a side note will this isolation transformer do the job
http://www.ebay.com/itm/271609192623?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
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Re: My new project

Post by 75X11 on Tue Dec 02, 2014 5:06 pm

That looks like a good one. Pretty nice price too.
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Re: My new project

Post by Guest on Tue Dec 02, 2014 7:30 pm

The variable transformer you got from me, allows you to slowly power up a radio without damage to it. An isolation transformer will protect you from electrocution should you become grounded. I use both together.

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Re: My new project

Post by Dr. Radio on Tue Dec 02, 2014 8:43 pm

Frank,

A variac affords not protection against electrocution due to the way it is wired.

http://www.tuberadioforum.com/t1915-step-by-step-restoration-ge-t-106c-let-s-go-for-it



The listing you provided looks like a good unit, but pricey. Be creative on your searching in eBay. Use the terms TRIAD and STANCOR with the word ISOLATION to broaden your search...

Here's one that would work for AC/DC radios:

http://www.ebay.com/itm/STANCOR-ISOLATION-TRANSFORMER-MODEL-GIS-100-NEW-/291114440853?pt=BI_Circuit_Breakers_Transformers&hash=item43c7c5d895


Just make sure the one you buy is meant to plug into 120 volts AC input and provides 120 volts AC output. (or in the olden days, listed as 115 volts) Some "step down", looking for 220 volts input.

Here's a good link on how to determine ratings:

http://www.antiqueradios.com/forums/viewtopic.php?t=130205
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Re: My new project

Post by frank1956 on Wed Dec 03, 2014 11:13 am

Just purchased my isolation transformer, should be here by next Tuesday.

Dr. Radio,
Have checked most of the resistors and they all are within or meet standards, there are two or three my digital or analog meter will not read, not sure why. Just for curious sake I changed out the .05 & .02 cap's also the 1200 ohm resistor per the schematic item # 12-21-28 with negative results.

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Re: My new project

Post by 75X11 on Wed Dec 03, 2014 1:37 pm

They may not be readable if they are open. Check your parts list and post what they should be for the benefit of all who follow this thread.
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Re: My new project

Post by frank1956 on Wed Dec 03, 2014 4:13 pm

All,
Went out and got me and all purpose meter that should serve my purpose from here on out. I re-took all my resistor reading and they are as follows. I have listed the schematics parts list first, followed by my reading.

1 22,000 = 21.2
2 Changed out two 100 ohm resistors for two 150 ohm resistors= 167.6 and 157.8
3 6,800 = 7.46 K
4 3.3 M = 3.7 M
5 47,000 = 47.0 K
6 1,200 = 1.18 K
7 10 M = 10 M
8 220,000 = 21 K
9 470,000 = 574 K

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Re: My new project

Post by Wildcat445 on Wed Dec 03, 2014 7:47 pm

I'd replace them all, except #5 and #7. #1 is iffy. I like 1% metal film resistors. I'll shut up now. Good luck.

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Re: My new project

Post by frank1956 on Wed Dec 03, 2014 8:17 pm

WC,
Why would you replace them all? Are they that far out of tolerance??

Frank
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Re: My new project

Post by Wildcat445 on Wed Dec 03, 2014 9:26 pm

Yep.  I don't buy the 20% tolerance.  #3, #4 & #9 especially are out.  Tolerance is not so critical in an AA5, but if you get into a Magnavox stereo, those reading would be enough to really mess things up.  If you adopt good practices in small radios, you will not have problems when you graduate to large consoles or even TV.  The only resistors I buy are 1% tolerance metal film resistors.  They are not that much more expensive.  Somebody may come on here and say that I am all wet.  That's fine.  Do it whichever way you think best.  I'm just telling you how I would do it.  If resistors have drifted as much as most of those have, what will they do when they get hot after running for awhile?  I personally feel that old, drifted composite resistors are as unreliable in a circuit as old, leaky capacitors.  I don't take anything for granted, even with new components, so I measure them before I put them in a circuit.  

Get on a TV repair website or look one up on YouTube. Find out how seriously TV guys take resistors. Some of those guys are seriously picky when it comes to resistors and how their operation affects a circuit. Horizonatal, vertical and some chroma circuits have critical resistors. In a Magnavox stereo amplifier, particularly dual-frequency models, that much difference in the grid resistors can take out other components, including transformers, and at the very least, give you are pretty sick amplifier. Just my two cents. Sorry to hijack your thread. Good luck.

WC


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Re: My new project

Post by 75X11 on Thu Dec 04, 2014 12:15 am

Frank, WC's advice is good. I got one of these for a couple of wattage ranges and put them in compartment boxes from big lots and have been using them in my projects. If money is tight, this could be a way to go. They are not metal film, though.

http://www.ebay.com/itm/365-PC-Carbon-Film-Resistor-Kit-1-2-Watt-Elenco-RK-365-/121484836072?pt=LH_DefaultDomain_0&hash=item1c490f7ce8
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Re: My new project

Post by frank1956 on Thu Dec 04, 2014 11:26 am

I use metal film @ 2%.

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Re: My new project

Post by frank1956 on Thu Dec 04, 2014 12:36 pm

Now that I am going through this radio with a fine tooth comb, I have notice some schematic discrepancies or at least I think they are. First one I notice is the schematic only calls for 2 100 ohm resistors (#8 and #16 which I changed out to 150 ohm per Dr. Radio), but I find 3 in the radio . I have attached a pic of what the bottom of the radio looked like before I started the restoration. The resistor in question is circled. It is brown-black-brown which if I do resistor color code should be 100 ohms??? If it is not correct can someone point me in the right direction, I have tried to trace the schematic out, but if the parts list is wrong maybe the schematic is????


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Re: My new project

Post by frank1956 on Thu Dec 04, 2014 1:07 pm

All.
I have taken the schematic and have traced all the known resistors in the radio (3 times). Per the schematic there are 10 resistors in the radio, I have 11. affraid  The one is question is the one on the previous post which I find no were on the schematic, maybe I overlooked it eye's are not what they used to be.
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Re: My new project

Post by Dr. Radio on Thu Dec 04, 2014 8:31 pm

Frank,

I'm on my mobile, so I can't answer all your questions by analyzing everything till I get to the laptop, but have some important points to make.

First off, I never said change BOTH 100 ohm resistors to 150 ohms. The only "150 change" is the one connected to the 50B5. Leave the 100 ohm in the oscillator 12BE6 alone. If the resistor is way off, then replace it with a new 100 ohm resistor.

Speaking of resistors, I must disagree with some statements made.

For a simple AC/DC AM radio, there is absolutely no need for precision 1 and 2 percent resistors. The 20% rule is fine in most circumstances. Things like televisions sync circuits and audio networks in a Magnavox where frequencies are critical, then yes, it's a different story. It's pretty obvious what resistors are way "off" in your measurements. Those need change out. 5 and 10 percent carbon resistors are just fine.

More thoughts on resistors...years ago there was an excellent discussion on ARF about resistor types. I need to look into the validity of this, but one poster said "no" to metal film resistors in certain applications. Since it's a thin "film" inside for the resistance element, these make a poor choice due to their inability to handle high peak/in rush currents. Power supply circuits would be a prime suspect to avoid. Now to be honest, I've used them, you'll be fine in your little Crosley, but something to think about (reading this Wildcat?) Smile

Another point is going with those super tight tolerances. 1 and 2 percent are great, but don't belong in "general" vintage circuits as the designers NEVER envisioned using that tight of tolerances. You can actually end up boosting voltages in circuits throwing off operation and causing premature failures. Again, for your simple Crosley, it's more of spending money you don't need to rather then you causing some catastrophic event in your radio.

Speaking of catastrophic events...have you checked the terminals on the IF transformer for proper coil resistance on each coil? That would be a bummer if one or both coils got "burned up" in the mishap.
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