I have an old tube Magnavox record console. It has the line cord directly connected to the chassis and circuit. (No mains transformer.) It seems hard to find a 1:1 transformer. The ones I'm finding are designed for benchtop use with a built-in socket and fuse. I just need a simple transformer. Is there any reason that I can't just wire two of these back to back? It would only be $22. Is there a flaw in my thinking here?
120/240V 56VA ISOLATION/UP-DOWN TRANSFORMER | All Electronics Corp.
120/240V 56VA ISOLATION/UP-DOWN TRANSFORMER | All Electronics Corp.
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I'll try to get a pic up a little later. This was actually fairly common "back in the day." I was reminded of this by someone who posted a similar amp over at AudioKarma. Note also, the chassis would only be hot if the plug was inserted the wrong way. But since this unit predated polarized plugs, that was a possibility.
I picked up a "Tripp lite" isolation transformer for $5 at a pawn shop. It's rated 3A and built more like it could do 15... Pretty large and heavy. Secondary has two std double AC outlets with film caps right across the AC output secondary plus MOVs in parallel with those. I think you can get one of your own to do this job. Mine looks exactly like this one -
TRIPP-LITE ISOLATOR IS400 Isolation Transformer 3.4A 400 Watt Hospital Grade | eBay
They arent cheap, unfortunately. If you can measure the AC power your little amp takes while running (using something like a "watts up" power meter) that would help you size the VA to come up with something a lot more reasonable in cost. You're headed in the right direction.
TRIPP-LITE ISOLATOR IS400 Isolation Transformer 3.4A 400 Watt Hospital Grade | eBay
They arent cheap, unfortunately. If you can measure the AC power your little amp takes while running (using something like a "watts up" power meter) that would help you size the VA to come up with something a lot more reasonable in cost. You're headed in the right direction.
Who made up that schematic?
Because it's an electrical disaster waiting to happen.
Whoever drew that has no knowledge or experience with fundamental electricity or electrical codes.
I just googled it.
Here's a better circuit with the central secondary connected to neutral.
Except that won't work for me,
the mains in my house don't have neutral, I have two live phases of 135v to earth that give together 233v,
here's a thread about it.
Here's a better circuit with the central secondary connected to neutral.
Except that won't work for me,
the mains in my house don't have neutral, I have two live phases of 135v to earth that give together 233v,
here's a thread about it.
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My valve amp test PSU is built exactly like that, using two back to back 230/245:110V isolation transformers.
If you figure 80% efficiency per transformer, or something reasonable, and de rate to say 60% VA rating or less.
Caveat: This is me saying it without doing the beermat maths.
Nice info. Thanks all. I had almost forgotten about this post.
I'll try to get that info this weekend. The console is "buried" in storage.
Btw, it's one of these. (Internet pic.) Oddly, it isn't stereo. Just two different cabs. Phono in one cab, (no tuner). Record storage in the other.
I'll try to get that info this weekend. The console is "buried" in storage.
Btw, it's one of these. (Internet pic.) Oddly, it isn't stereo. Just two different cabs. Phono in one cab, (no tuner). Record storage in the other.
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Re: Artie....
Those Magnavox units were the cheap offerings with optional stereo conversion capability for the record changer.
The ones using a "hot chassis" were made with any one of these chassis...(ink-stamped # on the chassis)
94-xx
99-xx
189-xx
194-xx
80-xx
They only put out about 3 watts to the speakers.
And being "hot", you have to plug the AC cord in the right way to prevent feeling "the tingle" when touching anything metal in the console. (a 0.047 cap is connected to the chassis)
Those Magnavox units were the cheap offerings with optional stereo conversion capability for the record changer.
The ones using a "hot chassis" were made with any one of these chassis...(ink-stamped # on the chassis)
94-xx
99-xx
189-xx
194-xx
80-xx
They only put out about 3 watts to the speakers.
And being "hot", you have to plug the AC cord in the right way to prevent feeling "the tingle" when touching anything metal in the console. (a 0.047 cap is connected to the chassis)
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