# Isolation transformers......



## Electraglide (Jan 24, 2010)

I need some isolation transformers for a few projects I have when it gets too cold to work on the bike this winter. They have to be smaller than 1.25 x 1.25 inches and they have to be inexpensive. All I need is the brand and the number. If they look like they're from the late 40's or early 50's so much the better. I'm not particularly interested in buying them off line and the Source/RadioShack in town no longer carries much dyi stuff.
My projects for this winter include turning a few old tube amp record players into small tube amps and getting two old "farm" radios working. The radios are 90 volt DC on the B side....anyone know where I can get a couple of EverReady 45v rechargeable radio batteries?


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## jb welder (Sep 14, 2010)

What exactly are you isolating? From the size, it sounds like they are not for handling power?
Or if they are, what kind of wattage do you require?


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## Church-Audio (Sep 27, 2014)

These transformers are rated in Volt amps the calculation into amps is.
I (a) = S (va) / V (v) 
The current in amps is equal to the apparent power in S volt amps. Divide the volt amps into V volts. So if we take 1000 volt amps and divide it by 120 = 8.33
So for example you don't really need more than say 2 1/2 amps for working on most radio circuits right? 
So thats 300vA divided by 120v = 2.5 A 
So you need a 300vA transformer.

I just want to say I know nothing about radio circuits!! but I do find them interesting good luck Check these links out.

http://www.jameco.com/1/1/1999-itr300-300va-isolation-transformer-input-120vac-60hz.html

Might want to build this simple circuit to eliminate the battery altogether. 

http://www.antiqueradio.org/bsupply.htm


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## Electraglide (Jan 24, 2010)

jb welder said:


> What exactly are you isolating? From the size, it sounds like they are not for handling power?
> Or if they are, what kind of wattage do you require?


Let's see, the amp from a 1959 RCA model K471 record player.... .38 amps. Not too sure of what the tube(s) are. Another is an older 1947 or so RCA model 45E record player (only -pays 45's)..... .40 amps. 1-12av6, 1-50c5, 1-35w4. The third is an RCA model HF195 record player.....not too sure of the amps. Tubes are 1-12ax7, 2-35c5, 1-35w4. The last is an old Viking record player from the same era...... .30 amps, 2-50eh5 tubes. There seems to be two little amps in this one, one per speaker. These are basically based on the old 'A' style radio amps that everyone recommends adding an isolation transformer to. Very similar to my Symphonic model MA1 amp. We're probably talking under 1.5 watts. I put down a physical size because depending what I use to build these amps I am limited in space. The HF195 might be kept as a working record player, not too sure yet.


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## Church-Audio (Sep 27, 2014)

I have a new in a box Hammond 169qs isolation transformer $50 shipped to Alberta. Its 348mA secondary. And its small. VERY Small. Bought it for a customer that never ended up using it.
I take paypal. And will ship with tracking and insurance. The transformer cost me $50 + shipping.


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## jb welder (Sep 14, 2010)

Smaller than 1.25 x 1.25 inch ?


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## jb welder (Sep 14, 2010)

The smallest here are cheap, but I think they are still too big for your spec. :
http://www.triadmagnetics.com/catalog_template.php?productCategoryId=65


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## Church-Audio (Sep 27, 2014)

The one I have his 2 inches bell to bell. X 2.63 tall x 2.19 wide.


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## Electraglide (Jan 24, 2010)

Amprepair said:


> These transformers are rated in Volt amps the calculation into amps is.
> I (a) = S (va) / V (v)
> The current in amps is equal to the apparent power in S volt amps. Divide the volt amps into V volts. So if we take 1000 volt amps and divide it by 120 = 8.33
> So for example you don't really need more than say 2 1/2 amps for working on most radio circuits right?
> ...


When I got the Stromberg Carlson radio I got 2 battery eliminators with it. One from the 40's I think and one from 1950/1952. Just figure it would be kinda interesting to have the batteries. The one eliminator is rated at [email protected] on the B circuit and [email protected] on the A circuit. Most of the old table radios I have are rated at under .5 amps. The record players are rated at about the same so I'm not too sure what using a 2.5 amp output transformer would do but I'd probably be smelling Bakelite. 
As far as the amplifier part of old .....before you were born... radio circuits go, almost all tube amps from before about 1965 are based on them. The radio part of the circuits is a bit more interesting. Get yourself an old tube radio or record player and check things out. Then build yourself a Crystal radio. Just be careful when you get the Cat's Whisker, the cats don't always appreciate that.
and I checked the link for the transformer.....too big, too much amp output and cost too much. But thanks anyway.


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## Church-Audio (Sep 27, 2014)

Just because a transformer can Supply 2.5 amps does not mean your going to fry anything  If you need .5 amps or 500 mA than you need at least an amp to be safe of total current capacity. I have built a crystal radio when I was a kid it was fun!! i have no desire to get into radios  I have a collection of vintage tube radios here nothing too exciting. But I do remember playing with tube portable record players when I was a kid I would open them up add speakers lol get shocked ect lol.


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## Guitar101 (Jan 19, 2011)

All of you guys blow me away with knowledge you have acquired with this stuff. I'm impressed.


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## Church-Audio (Sep 27, 2014)

And I am quite sure there are things you know that I don't know or others dont know. Nothing better than sharing knowledge. I dont like people that keep shit to themselves like its some secret club.


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## dcole (Oct 8, 2008)

If you can find it, I would think the cheapest source of isolation transformers would be from re-modeled older homes. I had a 20VA iso-transformer for my razor only plug in the bathroom. Maybe stuff like this arrives at the Re-Store or you could put feelers out on your local used sites.


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## jb welder (Sep 14, 2010)

Electraglide said:


> I need some isolation transformers for a few projects I have when it gets too cold to work on the bike this winter. They have to be smaller than 1.25 x 1.25 inches and they have to be inexpensive. All I need is the brand and the number.


Due to your size constraints, I don't think you will have any luck. On that triadmagnetics link I posted earlier, their smallest unit is only 15VA, but is still (physically) larger than what you need. (http://www.triadmagnetics.com/catalog_template.php?productCategoryId=65)
Perhaps a better solution would be a larger outboard unit. Then you can plug any of your non isolated units into it, as long as it has a high enough VA rating.


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## Lincoln (Jun 2, 2008)

Newark/Element 44 stocks a Triad N51X for $19.95 It's 35VA, close to the 38VA you mentioned. 300ma only thing is the size. It's over 2" square.

http://canada.newark.com/triad-magnetics/n-51x/transformer-115v-35va/dp/78K8611

http://www.farnell.com/datasheets/1820789.pdf


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