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 Post subject: Need Power Supply& testingTW-11 Tube Tester
PostPosted: Nov Sat 14, 2020 10:33 am 
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Joined: Jan Sat 23, 2010 3:08 am
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Location: The Great Pacific Northwest
Hi, what is best way to test power supply on this unit. I was going from common black to filament selector switch reading all the AC settings. This seems right am I missing something would it be better to test continuity of voltage tap. Right now power supply gets so hot wax coming out yiker shut it down quick. This was edited for a little more clarity,included schematic and hopefully better punctuation. : ) Thanks in advance.


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Last edited by frogpond on Nov Sun 15, 2020 3:52 am, edited 1 time in total.
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 Post subject: Re: Need Power Supply& testingTW-11 Tube Tester
PostPosted: Nov Sat 14, 2020 12:50 pm 
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Would be nice to see a schematic. I am seeing things possibly done in the wrong order. Long before parts were replaced some basic rudimentary testing should have been done to establish if the transformer was good and advice sought if you were not sure as to how to proceed.

Capacitors rather than resistors are the common failures and I see no reference to any filter capacitors or if they were changed? If it has them on the Power Supply and they are old & unused for who knows when, they can present as a short circuit and cause considerable damage to rectifiers & transformers. This is reading like that scenario.

Stop now! Post a schematic and confirm exactly what you replaced, rather than what you should have replaced & done first. You may now have to unload the transformer to establish its integrity.

Marc


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 Post subject: Re: Need Power Supply& testingTW-11 Tube Tester
PostPosted: Nov Sat 14, 2020 10:21 pm 
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Hi Marc, thank you for responding, I apologize for being vague.
Here is the schematic. I noticed testing a 24A tube it wasn't heating. I've had this unit for awhile, since 2014. I remember it working, but getting hot. I'm working from a isolation transformer to be safe and I've worked on radios in the past. I changed the 120 ohm resister, it read 128 ohms,changed .01mf capacitor to .02mf,I tested the 5k ohm resister it reads 5500 ohms. I was going to replace but it looks beefier than my 1/2 w resistor not sure about that so left it would that 1/2 w resister work?. Here is a picture of all components replaced their all around the short/ quality switch. As I stated, I was taking AC readings off black com and all the leads running into filament selection switch.


Last edited by frogpond on Nov Sat 14, 2020 11:57 pm, edited 2 times in total.

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 Post subject: Re: Need Power Supply& testingTW-11 Tube Tester
PostPosted: Nov Sat 14, 2020 11:33 pm 
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Last edited by Barry H Bennett on Nov Sun 15, 2020 4:51 am, edited 1 time in total.

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 Post subject: Re: Need Power Supply& testingTW-11 Tube Tester
PostPosted: Nov Sun 15, 2020 12:55 am 
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That is not what I personally would call a transformer, more of a tapped ballast. I would prefer to see the proper value cap and it be a line cap.

I normally use 1watt resistors to get the voltage rating 5K & 1K I would only replace with high watt (like 5) if that is what was there.

I have marked what wires I would consider disconnecting to test if the Ballast has got issues and would insulation test it. Some of that stuff is not "continuous rated", i.e. not designed to run all day or be in the test position for more than a few secs.

It would be advisable to check the condition of the wiring as cut through shorts & shorts caused by deterioration and switch breakages are not uncommon. A short is more the probability here if it had the same fault before it was touched.

Marc


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 Post subject: Re: Need Power Supply& testingTW-11 Tube Tester
PostPosted: Nov Sun 15, 2020 1:17 am 
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Joined: Jan Tue 10, 2012 8:39 am
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Be wary. There is no isolation. The top cap, for instance, can be hot with 120V in some settings, depending on orientation of the power line plug.

Looks like they saved a few cents by making the 25 and 35 Volt heater voltages the same.


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 Post subject: Re: Need Power Supply& testingTW-11 Tube Tester
PostPosted: Nov Sun 15, 2020 2:16 am 
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Thank you all for your input, I will make all the changes you recommend and see what happens. Point taken with hot voltage and much appreciated. Regards, Paul


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 Post subject: Re: Need Power Supply& testingTW-11 Tube Tester
PostPosted: Nov Sun 15, 2020 3:16 am 
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Yeh! Forgot to mention possible "live frame" or floating. That which I call a glorified ballast, falls into the same category as, no transformer, and auto transformers where no protection is on offer. That is also why I suggested line cap. One wold like to think that the fly lead was well insulated, or not installed whilst the machine was alive.

A thought: Here we have regulations that require double pole switches on utility (mains) sockets on motor homes & a few other things where wiring can get reverse phased (power cables) Where plug scan be reversed: converting to this type of switch on the work bench may be a safety option?

Do be aware that some European radios have this sort of ballast. It may look like a transformer, that does not mean it is: Beware.

Marc


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