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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 3:18 pm 
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pixellany wrote:
My comment applied to the 410....which is linked above

Here is where the Tamura 3FD-410 is used successfully to power radios.


http://solorb.com/elect/hamcirc/farmradiops1/index.html


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 4:43 pm 
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See the specs in 2 different places on the data sheet.

Each secondary is rated at 5 volts, 600mA....That's 3 VA

Later they show the total VA rating of 6VA, but that only applies if the two sides are effectively used in parallel. Wired as an isolation transformer, it's actually only good for 3VA!

Maybe this is OK for specific low-power battery radios, but definitely NOT good as a general-purpose iso transformer.

Even the Triad is marginal.......but: Why do you need anything in addition to what you already have?

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 5:17 pm 
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In an attempt to follow this thread, it appears the O.P. is pursuing two avenues, a power supply for a farm radio and a general purpose isolation transformer. Since it is possible to re-purpose a transformer this is an economical approach but all, operating parameters must be considered. Replies are to the point saying this is what you need xx-va, xx-volts ,etc. This works when the information about a transformer is known, for an unknown re-purposed transformer, it is a an educated guess based on what the device was intended to do in its past life. There are also budget considerations weighted against the "fun factor". Making something for purpose from junk...

I know what I would choose but the engine of my decisions is my wallet, safety first, the fun factor is a distant second place.

To the O.P. choose a transformer for the farm radio that does the job based on the current it can handle and volts needed. As for the isolation transformer the choice has to be weighed not only by the current but by any safety factor as a bench tool to service line power hot chassis receivers one is essentially placing there life on the correct choice.

YMMV

Chas

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 5:24 pm 
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Ozo wrote:
......... I have a 400 VA Isolation Transformer for everything else I might work on.

You only need one isolation transformer......for the device under test.

400VA should handle most radios...and even TV sets.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 6:00 pm 
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pixellany wrote:
You only need one isolation transformer..

If two is needed I swap out the variac for spare that's normally a door stop...


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 6:06 pm 
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pixellany wrote:
Ozo wrote:
......... I have a 400 VA Isolation Transformer for everything else I might work on.

You only need one isolation transformer......for the device under test.

400VA should handle most radios...and even TV sets.

I know that but as Chas remarked I want to build a small one with a home brew box for fun. This is a brand new hobby to me and more about fun than work. I do have a half dozen radios to refurbish so that will be a little work but I am sure there will be a little fun too. Still, the 50 VA Iso Xfmr will handle powering those on my bench. Beyond that it is hard to say what is going to happen.


Last edited by Ozo on Nov Fri 25, 2016 11:06 pm, edited 1 time in total.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 10:46 pm 
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I've mentioned this in the past, but since it's been a while, I'll bring it up again.

A source of cheap 20VA isolation transformers are the old razor outlets that you may find in your very own bathroom. If you have one, you can pull it out and replace it with a GFI outlet, and use the transformer for your radio projects. Better yet, visit your local surplus building material store (eg., Habitat for Humanity ReStore, etc.), look through the reclaimed electrical junk and pick up several of these transformers for next to nothing. Great little transformers with built in thermal protection that can supply enough power for the B supply of most tube hobby projects.


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 11:20 pm 
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Clever!

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Sat 26, 2016 6:09 pm 
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BobWeaver wrote:
I've mentioned this in the past, but since it's been a while, I'll bring it up again.

A source of cheap 20VA isolation transformers are the old razor outlets that you may find in your very own bathroom. If you have one, you can pull it out and replace it with a GFI outlet, and use the transformer for your radio projects. Better yet, visit your local surplus building material store (eg., Habitat for Humanity ReStore, etc.), look through the reclaimed electrical junk and pick up several of these transformers for next to nothing. Great little transformers with built in thermal protection that can supply enough power for the B supply of most tube hobby projects.

That's what I been using as well for years on my projects.

I acquired a box full of NOS razor outlets that were left over from a motel rebuild, I just tear one off the outlet plate as needed.


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Sat 26, 2016 9:25 pm 
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Ummm----time out. Almost any set I have worked in the last few years needed more than 20VA.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Sat 26, 2016 9:54 pm 
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Right. I'm not talking about using them for powering existing AC/DC radios. I just use them for the B supply in my own tube projects.


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Sat 26, 2016 10:13 pm 
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Rich, W3HWJ wrote:
If you intend to work on AA5 radios, you would need something like 50VA.

The tube heater string takes 0.15 A x 120 V = 18 watts. Probably another 5 watts max for B+ voltages. You might get away with 25VA, but why push it?

Rich
My next radio refurb is a Philco 46-421 which is 30 watts so the 50VA transformer should handle that. I am now looking at the rest of my old radios coming up for refurb to see what those power requirement are.
EDIT: The Philco 48-482 AM/FM I want to refurbish is 80 watts power consumption so the 50 VA transformer is too small for that , I will use the larger 400VA transformer I mentioned above.
Just to be clear, I am not working on any radios with power applied.


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Sun 27, 2016 6:08 pm 
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Location: aston, pa, usa
A source of cheap 20VA isolation transformers are the old razor outlets that you may find in your very own bathroom. If you have one, you can pull it out and replace it with a GFI outlet, and use the transformer for your radio projects. Better yet, visit your local surplus building material store (eg., Habitat for Humanity ReStore, etc.), look through the reclaimed electrical junk and pick up several of these transformers for next to nothing. Great little transformers with built in thermal protection that can supply enough power for the B supply of most tube hobby projects.Right. I'm not talking about using them for powering existing AC/DC radios. I just use them for the B supply in my own tube projects.


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Now we're a homebrewin'

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Sun 27, 2016 8:00 pm 
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bill hamre wrote:
A source of cheap 20VA isolation transformers are the old razor outlets that you may find in your very own bathroom. If you have one, you can pull it out and replace it with a GFI outlet, and use the transformer for your radio projects. Better yet, visit your local surplus building material store (eg., Habitat for Humanity ReStore, etc.), look through the reclaimed electrical junk and pick up several of these transformers for next to nothing. Great little transformers with built in thermal protection that can supply enough power for the B supply of most tube hobby projects.Right. I'm not talking about using them for powering existing AC/DC radios. I just use them for the B supply in my own tube projects
---------------------------------------------------------------------------------------------------------------------------
Now we're a homebrewin'



Bob Weaver just mentioned the same thing above. I am the OP and appreciate any input to my thread but do not have any tube projects. This thread is about a new guy building a Homebrewed (sorta) fifty VA isolation transformer for fun. :)


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Sun 27, 2016 9:02 pm 
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:idea: Gonna put a Dim Bulb tester on this enclosure. :idea: I will use a Variac, followed by the isolation transformer/Dim Bulb tester the first time I power up a radio (50 watt or less). This enclosure will keep the bulb from floating around on the bench. Just got a cheap plastic socket from Asia for 73 cents (after shipping) but will upgrade to porcelain from Goodwill later if I spot one.
http://www.ebay.com/itm/231587094656?_t ... EBIDX%3AIT


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Sun 27, 2016 10:15 pm 
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This thread is about a new guy building a Homebrewed (sorta) fifty VA isolation transformer for fun.
--------------------------------------------------------------------------------------------------------------------
Sorry, I didn't know it was off topic. Thanks for pointing that out.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Sun 27, 2016 10:45 pm 
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Ozo wrote:
:idea: Gonna put a Dim Bulb tester on this enclosure. :idea: I will use a Variac, followed by the isolation transformer/Dim Bulb tester the first time I power up a radio (50 watt or less). This enclosure will keep the bulb from floating around on the bench. Just got a cheap plastic socket from Asia for 73 cents (after shipping) but will upgrade to porcelain from Goodwill later if I spot one.
http://www.ebay.com/itm/231587094656?_t ... EBIDX%3AIT

No need for a dim-bulb if you have a Variac. (an an ammeter....)

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Sun 27, 2016 11:03 pm 
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pixellany wrote:
Ozo wrote:
:idea: Gonna put a Dim Bulb tester on this enclosure. :idea: I will use a Variac, followed by the isolation transformer/Dim Bulb tester the first time I power up a radio (50 watt or less). This enclosure will keep the bulb from floating around on the bench. Just got a cheap plastic socket from Asia for 73 cents (after shipping) but will upgrade to porcelain from Goodwill later if I spot one.
http://www.ebay.com/itm/231587094656?_t ... EBIDX%3AIT

No need for a dim-bulb if you have a Variac. (an an ammeter....)


You are right. I have a clamp on multimeter and can watch that for any indication of a short circuit in the power cord, failed electrolytic capacitors in the power supply, or other serious problems like shorted transformers not obvious to the naked eye. I will need the ammeter in series to monitor the DC current when I power the farm radio. I think I will still install the dim bulb - just for fun.


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Mon 28, 2016 2:53 am 
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Ozo wrote:
I will have to change fuses if I am working on a radio with a higher current requirement. Am I approaching this correctly?
You don't need a fuse if the Dim Bulb is in circuit. (Change bulbs)


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Mon 28, 2016 1:55 pm 
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If I power up a 50 watt radio with a 50 watt bulb in the circuit the 300 mA fuse will not blow? Would the 50 watt bulb still be the one to use?


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