Design inquiry/question- proper Earth and chassis ground in a floating power supply

[Supersonic Amplification]

Greetings, fellow enthusiasts.

So I am working on constructing a benchtop prototyping system so I can get to work on designing a new order. For the time being, I am left "PowerTransformerLess"- my beefy 700VA with 6.3v and 5v windings met an unfortunate end recently (don't ever use old filter caps- even if they check out just fine... Duh! Face palm) - and I cannot wind another one as I am out of suffiecient core materials. And I wouldn't if I could buy the same thing only slightly inferior (current wise) for 100 bucks. Simply put, I'm left with an alternative method:

I have a 45v - 0v - 45v  (90v across both) high current transformer salvaged from a SS P.A. amp- and have a voltage TRIPLER circuit already set up-  it yields about 380v without load, and sufficient current capability for up to 4 beam tetrodes- (about 750 mA)

 I am concerned about the safety of having the secondary voltage "floating". I will post a schematic of the circuit in question shortly.

My question is- how should I reference the secondary and the tripler to earth and chassis? Theoretically I could simply Earth one side of the secondary (the secondary CT is floating in the current configuration for the full 90 volts)- but I am unsure of the consequences that may arise...

This device will need to be UL listed after the prototype is built- so extra EXTRA end user safety is imperative.

Any comments or tips would be graciously accepted and appreciated!!

Thanks in advance!!

Tommy P.
Lead Engineer | Supersonic Amplification

[tubeswell]

... I will post a schematic of the circuit in question shortly...

Please do

[Supersonic Amplification]

Forum says my picture is too large. My cameras lowest quality is still larger than 800 kB. Can't find a way to easily compress it, you know how smart phones are… but it's a standard voltage tripler circuit. Commonly found in the electronics textbooks. All diodes are 1n4007 and Capacitors are 8, 8, and 16 µF at 450 working volts. The center tap is floating on the secondary and the secondary is not currently grounded. My question is how to properly ground the secondary to earth without causing electrocution. Lol

[HotBluePlates]

Forum says my picture is too large. My cameras lowest quality is still larger than 800 kB. Can't find a way to easily compress it, you know how smart phones are…

Use your computer.

Got a Windows machine? You can resize pictures in MS-Paint or in MS Picture Manager.

[kagliostro]

Host the image (Free) at Imgur and post here the link using the image option you see under the Bolt button when you post

http://imgur.com/

Franco

[eleventeen]

1: I wouldn't be designing stuff using voltage triplers UNLESS the desired product used tiny, tiny current, talking about 5 mils, 10 mils. That would rule out tube amps right away.


2: It is a bit tricky to derive bias voltage for output tubes from doublers and triplers and my experiences suggest that this is not a good way to go, because B+ and bias interact and component values affect output voltages. Me? I wouldn't go that way.


3: How many hours are you going to put into this thing, and what is the value of your time versus the $100 you are reluctant to spend? You can't go find a dead something (not a tabletop radio) at a thrift store or your local e-recycling joint? You can't place an ad to buy dead tube-type TV sets on Craigslist?


4: And where are you going to get your 6.3 volts if your voltage tripler works perfectly? Isn't that a tranny you are going to have to buy and while it should not be anywhere near $100, IMO you are engaging in false economy. 


5: Trust me, I started messing around with this stuff back in the 60's and a tube socket was 25 cents and a pot was 50 cents and a 12AX7 was $1.28 and guess what? That was more money than I wanted to spend back then and it was a lot of money for a kid. And it very likley cost me more time to earn $1.28 for a 12AX7 than it does $15 for a 12AX7 today. But when I contemplate building an amp and there's almost $20 in tube sockets, it tweaks my brain.


You can only scrounge so deep!


 

[HotBluePlates]

... This device will need to be UL listed after the prototype is built ...

This sounds like a consumer product, so ...

... my beefy 700VA with 6.3v and 5v windings met an unfortunate end recently ... and I cannot wind another one as I am out of sufficient core materials. ... Simply put, I'm left with an alternative method ...

... why are you going down the lash-up path (salvaged PT and voltage-tripler)?

Separately, The chassis should be bonded to the ground wire of the power cord feeding the primary side of the power transformer, as a way to trip a panel circuit breaker when there's a short to chassis. However, the entire circuit inside (from PT secondary and after) can be floated off the chassis, and indeed that's how you'd implement a ground-lift to break hum loops. Lots of UL, CE and ETL certified products are built this way, including double-insulated devices like power tools.

... 380v without load, and sufficient current capability for up to 4 beam tetrodes- (about 750 mA) ...

380v * 0.75A = 285 watts. Are you designing/building a bass amp?

[Supersonic Amplification]

Thanks for the replies guys- simply put, I'm at the moment broke. I can't afford a PT or core materials right now- @HotBluePlates, I wouldn't elect to use such a supply in the end model unless it did indeed function well, reduce cost, and was safe. It simply occured to me that this may work for reducing tranny size as well in the user model. But for prototyping on my desk for right now, I hope that this will work- but I could very well be wrong! eleventeen made some good points above with regard to current. I thing this tranny is rated for 90 volts at 8 amps- so I figured it may just work. But, again, I'm nineteen, what do I know?  (Just kidding) (kinda) I am very open to correction and input. What I don't want is a nasty shock if I go to touch the guitar strings or chassis when testing. Lol. It could technically wait, but I told the customer I was cooking something up. The sooner I have a working prototype, the better. Ya know? But I don't want to rush things, for sure.

[PRR]

Floating winding is non-issue. Especially since it can't float to infinity, but is effectively "tethered" by the doubler/tippler affair.

You are broke but plan on UL certification? That does not add up. UL wants large wheelbarrows of cash. There are other test labs who will do it for small wheelbarrows of cash. The cheapest will be hundreds of times more than a "right" power transformer. Note that if you significantly change the PT (run out of 45-0-45 SS amps), UL will expect a re-test.

[eleventeen]

A UL certification is about a $15K affair. To start. That's for a little 1 RU thingy (like I manufactured for a while) where the 120 VAC hits a transformer and past that, there's nothing over 12 or 15 volts. That was 20 years ago.


I hope you understand and it sounds like you do, I am not trying to discourage you from anything as far as trying ideas. I can tell you, if it was 1936 and you had to save up for every resistor and cap in something you wanted to build, that would be one thing. THAT I would discourage you from getting into in the 21st century.