ON a mains connected unit, if you never make a mistake, there is no problem. How perfect are you? If your probe slips, the ball of fire can be 6" diameter. If you touch two things with two hands, the current across your heart can be 20 amps and cause severe burning besides the stopping the rhythm section of your heart.
On a transformer connected unit, the ball of fire might just burn the tip off your meter, and nothing will burn if you have electricity crossing your body. My probe slipped enough times I had to replace the 5 ohm collector resistor of my most recent amp 6 times. I hope you are perfect, but don't plan on it.
You can put a plug and socket and fuse on the isolation transfomer and keep it entirely separate from your record player, or you can install one plus the fuse inside the chassis with the hot and neutral going where the old one did. In 1950, there was no separation of hot and neutral, and houses from that era have the plugs wired sort of randomly anyway, if not updated. Today the neutral is the big flat blade.
The selenium rectifier in my dynaco ST70 built 1961 was bad by 1970. They were amazing for 1961, but not very long lived. Silicon diodes were $20 in 1961, $.07 now. Get the rectifier and resistor on the same order as the isolation transformer. A 500 VA one could be big enough, read the watts on your dataplate if the device has one and get something bigger. .
The selenium rectifier has a mount, the 1n4007 won't. Plus on the selenium rectifier is the not line end of the 1n4007. I buy solder terminal strips from tubesandmore.com or triodeelectronics.com to put soldered components on old devices with a screw to the chassis. You'll have two devices, the 1n4007 and the 200 ohm 1w resistor, so buy a 3 terminal or more one. I use elastic stop nut screws so they don't come loose and float around later.
On a transformer connected unit, the ball of fire might just burn the tip off your meter, and nothing will burn if you have electricity crossing your body. My probe slipped enough times I had to replace the 5 ohm collector resistor of my most recent amp 6 times. I hope you are perfect, but don't plan on it.
You can put a plug and socket and fuse on the isolation transfomer and keep it entirely separate from your record player, or you can install one plus the fuse inside the chassis with the hot and neutral going where the old one did. In 1950, there was no separation of hot and neutral, and houses from that era have the plugs wired sort of randomly anyway, if not updated. Today the neutral is the big flat blade.
The selenium rectifier in my dynaco ST70 built 1961 was bad by 1970. They were amazing for 1961, but not very long lived. Silicon diodes were $20 in 1961, $.07 now. Get the rectifier and resistor on the same order as the isolation transformer. A 500 VA one could be big enough, read the watts on your dataplate if the device has one and get something bigger. .
The selenium rectifier has a mount, the 1n4007 won't. Plus on the selenium rectifier is the not line end of the 1n4007. I buy solder terminal strips from tubesandmore.com or triodeelectronics.com to put soldered components on old devices with a screw to the chassis. You'll have two devices, the 1n4007 and the 200 ohm 1w resistor, so buy a 3 terminal or more one. I use elastic stop nut screws so they don't come loose and float around later.
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Well I now feel like my head is going to properly explode haha, but better that I do things right the first time with awesome advice like yours indianajoe. Did you like the picture of my book?lol
Also like I said, I'm not a noob to electronics, but am ver much a noob when it comes to, how,what,and where to buy,use and connect them in "this" said application. Any advice on where to buy this isolation transformer and what "one" to buy and how to install it, or make it separate if need be would be really appreciated 🙂
I'd use eBay and Google. My first inclination would be to check Antek- they'll call it a power transformer, but the main thing is to have the ability to connect it for 10V:120V.
That is 120 VAC to 120 VAC. Antek is cheap, mounting parts must be bought on the same order, I haven't figured out how to do it.
See this 72-6670 - TENMA - ISOLATION TRANSFORMER | Newark comes in a box with cord, fuse outlet. If you know what wattage you device uses, you may be able to get away with something cheaper. That one is 450 watts, enough to do my ST70 for example.
I learned to wire from a Sears Roebuck pamphlet in 1962. but a lot has changed since them.
See this 72-6670 - TENMA - ISOLATION TRANSFORMER | Newark comes in a box with cord, fuse outlet. If you know what wattage you device uses, you may be able to get away with something cheaper. That one is 450 watts, enough to do my ST70 for example.
I learned to wire from a Sears Roebuck pamphlet in 1962. but a lot has changed since them.
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so in theory, if i never probe or touch the internal amp when the device is on and "hot" as in plugged in to the wall, then should never have a problem correct? And I should also put a new power cable on it with the correct polarity? or will that make no difference? And seen as i got this thing for free, im not looking to drop $64 bucks just for a pre-built isolation transformer. Now if there is one I could purchase for around $20 and install it myself, that would be more reasonable for what I am looking to spend on this record player. Obviously safety is of great importance to me, but my question is, "is a isolation transformer necessary if I am not going to be probing around while it is plugged in or on? And since this is a single tube amp, Im going to take a guess and say it probably not higher then 450amps, probably much lower, would that be a good guess?
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The problem is that there are inevitably metal parts that an innocent user can touch and.... ZAP! There's a reason that direct mains powering for a device like this is illegal and against Forum rules- it's basic user safety.
A 500W isolation transformer is total overkill- this is a small record player! 100W is more than enough.
A 500W isolation transformer is total overkill- this is a small record player! 100W is more than enough.
Thanks 🙂 Well I would be intrested in perhaps where I can find a small iso trans that will fit in this thing, and how I would go about wiring it?? Thanks a bunch for your help SY! I really appreciate all the advice and patience you have given me as a new member 😀 Could you perhaps post some liks in this thread of where I would be able to get a small low profile iso? Its one of these Google Image Result for http://images1.showmethead.com/nlarge/vintage_decca_record_player_model_dps_8_for_20_20516345.jpg so its going to need to be maby 2 or 3 inches tall at most, the only difference with my model is its almost exactly like this except its a 3 speed and has a grill where the speaker holes are on in the one in the picture link.
Try calling it a "power transformer" in your search- same thing, just that the term "isolation transformer" describes how you're using it and implies that primary and secondary have the same voltage.
The $62 device I suggested is a tool, which would not be installed in the record player and which might be useful for later projects. It has a steel box, a plug, receptacle, and fuse, as is appropriate for a tool. You need to learn now to use search tables on vendor websites. For example, you want one 120 vAC coil, you want one 120 vac out, probably center tap but not required, you want a certain minimum number of volt amps (watt surrogates) based on what wattage the label says, or what fuse your device has, or what size wire the power cord is (See National Electrical Code for safe current of three wires in a conduit). I'm not going to do the search for you. You may have a maximum dimension requirement. I've looked at antiqueradiosupply (tubesandmore.com) and triodeelectronics.com, both cater to antique radio hobbiests, that have this trouble all the time, and neither had anything. I found one possible solution at newark.com , a supplier I use in NC. Other suppliers people like are mouser.com in TX, and digitech.com, I don't know where their warehouse is. Some people love E-bay, I find their software locks up my computer and their last minute bidding is hidious. But enjoy yourself, it is your money. Antique radio repair sites may be more help in specifics, there are a lot of no transformer 7 tube AM radios out there produced in the fifties.
I'd like to re-iterate, toroidal transformers are state of the art, but unless you are great with a router and have a supply of dry maple logs, I haven't figured out the safe way to mount the **** things. Obviously a piece of heat formed plastic is the right thing, but such things to not come up on the "you might also want to buy" box of the websites I try selling torriodal transfomers. Including Antekinc.com. Toroids also are not 98% flux shielded like E-core transformers with copper or steel wrappers, so I don't know how people deal with the hum emitting from them, either. A grounded steel box just for the transformer is the brute force solution that comes to mind.
I'd like to re-iterate, toroidal transformers are state of the art, but unless you are great with a router and have a supply of dry maple logs, I haven't figured out the safe way to mount the **** things. Obviously a piece of heat formed plastic is the right thing, but such things to not come up on the "you might also want to buy" box of the websites I try selling torriodal transfomers. Including Antekinc.com. Toroids also are not 98% flux shielded like E-core transformers with copper or steel wrappers, so I don't know how people deal with the hum emitting from them, either. A grounded steel box just for the transformer is the brute force solution that comes to mind.
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Wow thanks indianajoe, that's a lot of great info! You rock for taking the time to type that all out for me 😀 Well If I have a transformer left over from say a computer power supply, how can I test It on a multimeter appropriately, to see what its putting out, or if testing it is even possible??? Also I havea smaller low profile one left over from an analog video enhancer box by Realistic, it has 2 leads soldered to it on one side, not sure if that is enough?
Multimeter test is only good for condemning a transformer because one winding or another is grounded to the frame- at 2 vdc. You can figure out which windings are connected to what with a multimeter. You could connect a transformer winding to a light bulb box or variac to see what comes out of the other leads, AC. But the variac or light bulb doesn't isolate the transformer from main AC feed, for that you need an isolation transformer. Or make **** sure you know which lead is the neutral lead. No mistakes. You touch the hot side even through a winding you thought was the secondary, you get lit up. you guess wrong on the input vs the output, you get 600 vac out instead of 24 vac.
Many transformers don't have enough windings to resist 120 VAC. Switcher computer power supplies, the transformers are not designed to resist 60 hz, they operate at 1200 hz or higher. These will light up the light bulb, probably. I'm leaning into junk transformer testing this week, makes me very nervous. I need 24 VAC @ 20 ma, which is tiny. I have a couple of 24 VAC at 1 amp transformers, they are bigger than the spare space I have to put it in. I have this old terminal PWB from the 60 hz transformer days. Three little transformers on it. You can tell vaguely what winding a transformer is by the dc rating on the caps running off of it, but at this age, the e-caps are likely to explode when powered up. Or, if you take the caps out out to be safe, you forget what the voltage rating was.
Many transformers don't have enough windings to resist 120 VAC. Switcher computer power supplies, the transformers are not designed to resist 60 hz, they operate at 1200 hz or higher. These will light up the light bulb, probably. I'm leaning into junk transformer testing this week, makes me very nervous. I need 24 VAC @ 20 ma, which is tiny. I have a couple of 24 VAC at 1 amp transformers, they are bigger than the spare space I have to put it in. I have this old terminal PWB from the 60 hz transformer days. Three little transformers on it. You can tell vaguely what winding a transformer is by the dc rating on the caps running off of it, but at this age, the e-caps are likely to explode when powered up. Or, if you take the caps out out to be safe, you forget what the voltage rating was.
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HOLY CRAPOLA!! I have alot to learn 😀 I just found this really cool and informative on how transformers work Understanding How Transformers Work I would preferably like one that was small enough to fit inside this tiny bugger of a suitcase turntable, but it seems that may prove difficult to find 😛
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