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Can I use a 120V Variac to get 220V?
I want to reform the electrolytics in an amp I'm bringing back to life.
It runs high power, 220 volts ac only. Can I use my 110 volt variac in conjunction with a 110V to 220V step-up transformer to power up the amp? Obviously I'd not go key-down, but I do want to ultimately get to the full B+ on the tubes. How would I wire-up the variac / transformer, assuming it's possible? Thanks in advance for the help, guys. 73, Jeff W8KZW |
Can I use a 120V Variac to get 220V?
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Can I use a 120V Variac to get 220V?
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Can I use a 120V Variac to get 220V?
Hi Jeff, Wire the output of the variac to the primary of the transformer, and the secondary to the 220V power input of the Amp. You may want to remove the tube(s) or disable the filaments to reduce the burden on the step up transformer. If the power transformer in the amp has a 110v tap, connect it up and then just use the variac. Be careful when you are doing this, there are all sorts of lethal voltages present. Good luck. Gary N4AST Thanks, Gary, but the devil is in the details. The 220 out from the step-up transformer is from one end of the secondary coil to the other. The amp is essentially asking for two 110 V lines, working against a common "ground". So, somehow I must go from this: 0 -----220----- 0 to this: 0 0 0 and therein lies my confusion. Here are the connectors labeled: 0 0 A B to this: 0 0 C D 0 E .... all I need to do is to connect the dots! |
Can I use a 120V Variac to get 220V?
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Can I use a 120V Variac to get 220V?
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Can I use a 120V Variac to get 220V?
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Can I use a 120V Variac to get 220V?
John, N9JG wrote:
Your advice is elegant in its simplicity. And OPTIMISTIC in it's generality. While one might imagine situations where this technique is useful, it would be better to define a strategy that takes into consideration the exact configuration of the PS in your unspecified amplifier. If your caps don't need reforming, any technique will work. If they do, you're gonna have some current flow. It's not hard to imagine a scenario whereby you have 25W or more dissipated in your caps. I don't call this safe. A 100W light bulb will keep you from blowing up the rectifiers while you're blowing up the caps. Assuming you have solid-state rectifiers, go back to the variac and transformer. Depending on the value of the high voltage, There may be issues if you just turn off the tube filaments. The series lamp can still be helpful, but isn't the whole story. It's always helpful to disclose the parameters of the situation when asking for advice. Otherwise, you'll get 10 different solutions based on 10 different assumptions, none of which will be correct. mike "Andrew VK3BFA" wrote in message oups.com... wrote: I want to reform the electrolytics in an amp I'm bringing back to life. It runs high power, 220 volts ac only. Can I use my 110 volt variac in conjunction with a 110V to 220V step-up transformer to power up the amp? Obviously I'd not go key-down, but I do want to ultimately get to the full B+ on the tubes. How would I wire-up the variac / transformer, assuming it's possible? Thanks in advance for the help, guys. 73, Jeff W8KZW Its relatively simple and easy. Connect a 100w light globe in series with the ac power input - this will limit current to a safe level. Run for 10 hrs or so, will give caps a chance to reform....start with the tubes in so the filament current draw limits cap voltage, then later remove tubes to get virtually full voltage across caps.... Andrew VK3BFA. |
Can I use a 120V Variac to get 220V?
mike wrote:
John, N9JG wrote: Your advice is elegant in its simplicity. And OPTIMISTIC in it's generality. While one might imagine situations where this technique is useful, it would be better to define a strategy that takes into consideration the exact configuration of the PS in your unspecified amplifier. Gee, that sounds like the opening page of a PowerPoint presentation - your not a manager by proffession, are you? And if you have an engineering degree, and want to engage in endless metaphysical speculation, thats a very good idea.....whatever it was.....amongst the verbiage.... If your caps don't need reforming, any technique will work. If they do, you're gonna have some current flow. It's not hard to imagine a scenario whereby you have 25W or more dissipated in your caps. I don't call this safe. A 100W light bulb will keep you from blowing up the rectifiers while you're blowing up the caps. Rubbish. Where do you get this 25w figure from, and across how many capacitors in a (typical) series string - oh, and lets ignore idling current through transformer and bleeeder resistors, and filamnet current drain, and blowers, and dial lamps, and.....which would further reduce available volts across the caps.... And whats this "imagine a scenario" stuff - I thought you were trying to be precise and were chiding me for my lack of hard data.... Assuming you have solid-state rectifiers, go back to the variac and transformer. Depending on the value of the high voltage, There may be issues if you just turn off the tube filaments. The series lamp can still be helpful, but isn't the whole story. So, what voltage do you set the variac too? - how do you work it out? It's always helpful to disclose the parameters of the situation when asking for advice. Otherwise, you'll get 10 different solutions based on 10 different assumptions, none of which will be correct. mike True. There are probably 10 different ways of puting out a fire, but the easiest is dumping a bucket of water on it. Honestly, this is ridiculous - most modern (ie, last 40 years) caps are fine, will survive horrendous abuse, and unless you have the manufacturers data sheets for these capacitors, (and the power transformer, and the rectifiers) how are you going to set these parameters anyway? - this is a linear amplifier, not the space shuttle. Why do people insist on making things sooooo complicated, almost theoretical physics level - it isnt. Dont let irelevant theory get in the way of practical electronics. The intial switch on of ANYTHING that hasnt been powered up for years is going to be the time it dies - at least the bulb will stop it bursting into flames, the variac method will jsut slowly ramp up volts until something blows catasphropically (I know, used to do this, got sick of replacing fuses in the variac.) As well, you have the added complication of multiple, lashed together transformers which MUST all be correctly phased and able to take the load current . a recipe for confusion at least. And no, I cant spell. Spend too much time with soldering irons rather than physics journals. Andrew VK3BFA. "Andrew VK3BFA" wrote in message oups.com... wrote: I want to reform the electrolytics in an amp I'm bringing back to life. It runs high power, 220 volts ac only. Can I use my 110 volt variac in conjunction with a 110V to 220V step-up transformer to power up the amp? Obviously I'd not go key-down, but I do want to ultimately get to the full B+ on the tubes. How would I wire-up the variac / transformer, assuming it's possible? Thanks in advance for the help, guys. 73, Jeff W8KZW Its relatively simple and easy. Connect a 100w light globe in series with the ac power input - this will limit current to a safe level. Run for 10 hrs or so, will give caps a chance to reform....start with the tubes in so the filament current draw limits cap voltage, then later remove tubes to get virtually full voltage across caps.... Andrew VK3BFA. |
Can I use a 120V Variac to get 220V?
Andrew VK3BFA wrote: mike wrote: John, N9JG wrote: Your advice is elegant in its simplicity. And OPTIMISTIC in it's generality. While one might imagine situations where this technique is useful, it would be better to define a strategy that takes into consideration the exact configuration of the PS in your unspecified amplifier. Gee, that sounds like the opening page of a PowerPoint presentation - your not a manager by proffession, are you? And if you have an engineering degree, and want to engage in endless metaphysical speculation, thats a very good idea.....whatever it was.....amongst the verbiage.... If your caps don't need reforming, any technique will work. If they do, you're gonna have some current flow. It's not hard to imagine a scenario whereby you have 25W or more dissipated in your caps. I don't call this safe. A 100W light bulb will keep you from blowing up the rectifiers while you're blowing up the caps. Rubbish. Where do you get this 25w figure from, and across how many capacitors in a (typical) series string - oh, and lets ignore idling current through transformer and bleeeder resistors, and filamnet current drain, and blowers, and dial lamps, and.....which would further reduce available volts across the caps.... And whats this "imagine a scenario" stuff - I thought you were trying to be precise and were chiding me for my lack of hard data.... Assuming you have solid-state rectifiers, go back to the variac and transformer. Depending on the value of the high voltage, There may be issues if you just turn off the tube filaments. The series lamp can still be helpful, but isn't the whole story. So, what voltage do you set the variac too? - how do you work it out? It's always helpful to disclose the parameters of the situation when asking for advice. Otherwise, you'll get 10 different solutions based on 10 different assumptions, none of which will be correct. mike True. There are probably 10 different ways of puting out a fire, but the easiest is dumping a bucket of water on it. Honestly, this is ridiculous - most modern (ie, last 40 years) caps are fine, will survive horrendous abuse, and unless you have the manufacturers data sheets for these capacitors, (and the power transformer, and the rectifiers) how are you going to set these parameters anyway? - this is a linear amplifier, not the space shuttle. Why do people insist on making things sooooo complicated, almost theoretical physics level - it isnt. Dont let irelevant theory get in the way of practical electronics. The intial switch on of ANYTHING that hasnt been powered up for years is going to be the time it dies - at least the bulb will stop it bursting into flames, the variac method will jsut slowly ramp up volts until something blows catasphropically (I know, used to do this, got sick of replacing fuses in the variac.) As well, you have the added complication of multiple, lashed together transformers which MUST all be correctly phased and able to take the load current . a recipe for confusion at least. And no, I cant spell. Spend too much time with soldering irons rather than physics journals. Andrew VK3BFA. All he was asking was how to hook up a variac. Seemed simple enough. Gary N4AST |
Can I use a 120V Variac to get 220V?
On Sun, 20 Aug 2006 08:11:33 GMT, mike wrote:
John, N9JG wrote: Your advice is elegant in its simplicity. And OPTIMISTIC in it's generality. While one might imagine situations where this technique is useful, it would be better to define a strategy that takes into consideration the exact configuration of the PS in your unspecified amplifier. If your caps don't need reforming, any technique will work. If they do, you're gonna have some current flow. It's not hard to imagine a scenario whereby you have 25W or more dissipated in your caps. I don't call this safe. A 100W light bulb will keep you from blowing up the rectifiers while you're blowing up the caps. I had this happen with a 3 week old amp. One of the low voltage caps blew. It sounded like a shotgun being fired in my basement. The "can" hit the top of the 8877 amp and flattened out like a 38 wadcutter hitting something solid. It doesn't have to be a boat anchor to have a cap blow. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com |
Can I use a 120V Variac to get 220V?
Thanks for the (mostly helpful) replies, guys.
Applying each one of the two ends of the 220V coil of the transformer to the 220V legs of the amplifier plug made sense. I guess I was mostly wrestling with how to handle the gounded / grounding lug of the amplifier plug. Gary said to just leave it floating, but wouldn't grounding it be safer? |
Can I use a 120V Variac to get 220V?
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Can I use a 120V Variac to get 220V?
j All he was asking was how to hook up a variac. Seemed simple enough. Gary N4AST True. But why lose the chance for an argument? - my issue was with the over complication of a simple task....and if someone needs to ask questions on how to set up a variac and a transformer, then the keep it simple approach (ie, the light bulb) has much to recomend it. Andrew VK3BFA. |
Can I use a 120V Variac to get 220V?
Andrew VK3BFA wrote:
tirade 1 deleted Rubbish. Where do you get this 25w figure from, tirade 2 deleted Well, you could do the math...it's easy. I was too lazy to do the nonlinear math for the lamp. But an experienced (good) engineer knows how to quickly make approximations to weed out BAD ideas. That skill is uncommon. You'd think it's obvious. And the GOOD engineers do it instinctively. But the other 99% just don't get it. They'll head down the dead-end road 'till they reach the end then bang their head on the barricade. A (good) engineering manager shines a light on those dead-end barricades. See, there are situations where a light bulb can fix a problem. When the problem is largely unspecified, a (good) consultant requests specificity. It's easy to ASSUME that it doesn't have tube rectifiers, but we don't really know. When the consequences can be BAD, and the problem is unspecified, a (good) consultant recommends a conservative approach. And when the original poster merely requested clarification on a conservative approach, it's low risk. Proposing a higher risk option is ill advised. A (good) teacher tries to understand the implications of the question and keep the student out of harm's way. I'm gonna pull some numbers outa my ass, 'cause that's where I keep my common sense. That way, I get a new supply every day. The series light bulb likely works 99.99% of the time. But doing nothing probably works 99.98% of the time. If your estimates are different, state them. How many times have you turned on your amp? How many times has it blowed up because you didn't reform the caps? At the risk of repeating myself...IF your caps NEED reforming, it's wise to bring them up slowly with a variac. Adding the series light bulb will make it even safer, but only if appropriately sized and you're paying attention...there's that pesky specificity again. If you're really interested in reforming caps, take them out and use a variable power supply with a BIG resistor separately for each one. Do it very slowly...but nobody really asked that... Ya see, if you've got series caps...more pesky specificity... a leaky one can cause the good one to fail. But nobody aked that either. And maybe they've got equalizing bleeders that can mitigate the problem...assuming one's not open and making the situation worse...but nobody asked that either. An interesting question might be, "how do you refurbish an amp that hasn't been turned on in a while?" But nobody asked that... Shooting from the hip, firing off the one true, onesizefitsall, solution when you don't know the particulars and are not accountable for the result is... well...it's the "internet way"! mike |
Can I use a 120V Variac to get 220V?
mike wrote:
Andrew VK3BFA wrote: tirade 1 deleted Rubbish. Where do you get this 25w figure from, tirade 2 deleted Well, you could do the math...it's easy. Shooting from the hip, firing off the one true, onesizefitsall, solution when you don't know the particulars and are not accountable for the result is... well...it's the "internet way"! mike RANT ON................................................ .................................. I am NOT disputing your theory - its correct as far as it goes, youve left out lots of other factors that, ideally, should be considered in this case, But its irrelevant to the original question. And in real life I would ignore it as being too anal retentive. If the original poster needed to ask how to hook up two transformers, then your quasi mathematical analysis would be totally innapropriate to the job specifications. Did you think of this at all? It is covered in most 1st year engineering course...(RTFM) My method, with the light bulb, might be crude, (it is crude, so?) but it will work. And have proved that it works, more times than I can remember. Linear and switching power supplies. A simple question - using the light bulb method, whats the WORSE that can happen? If the amp is horribly faulty (and lets not even bother about doing insulation tests on the (old) transformer, that would make it even more complicated) then the light bulb will light to full brilliance. Even an engineer could see that theres something wrong, and then fault find it. (After doing the math, of course) The variac method - again, the same simple question - whats the WORSE thing that could go wrong. And I will answer that, not from theory, but from practice. The voltage is slowly ramped up until something fails abruptly and catastrophically. With no current limiting beyond a mains fuse in the variac (You did check its rating, didnt you?) the electros will disintigrate like shotgun cartridges generating lots of additional work. (no harm was done to the person, being a trained engineer they had safety goggles on...didnt they?) (The above assumes its a linear supply - if its SMPS, then the switching devices sacrifice themselves in a vain attempot to save the fuse) I have spent my entire working life in this field - working as a technician fixing up the design problems of engineers. Stuff that any competent technician would know NOT to do, from practical experience. In my working life, I have met approx 5 competent engineers. The rest were theoretical bull**** artists who soon moved into management purely on the strength of having a degree - they were as hopeless at that as they were at engineering, but there they had less chance to do actual damage. Are you a "working" engineer - do you own a soldering iron? - lots of theory, plenty of if/but/maybe/ because/planning, but no real appreciation of what the problem is - firing up an old amplifier. Thats all - its not a design exercise, theres no cahce of a Nobel Prize in this one, the project doesnt need to be managed, no consultants needed to give a "proffessional " opinon, no SPICE models needed - just how to power up an amplifier with minimal damage. RANT OFF............................................... ................................................ woo........ TIRADE ON................................................ .............................................. And I am heartily sick of "armchair experts" making life bloody complicated when someone asks a legitimate question that is best answered without a theoretical textbook analysis - I have seen far too many people at radio clubs made to feel inadequate because some smartarse engineer has given a long winded incomprehensible, irrelevant answer to a simple question. These people leave, and dont bother to come to any more meetings, or ask any more questions. One of the best teachers I ever had was an engineer - a very rare person, a brilliant teacher and a competent engineer. He woked out where the question was coming from, ie the level the student was capable of understanding - he then started from basic principles, with great patience, and took the student forward until they could understand the rocket science behind the question. And if you want to see a good textbook using this method, grab a copy of 'The Art of Engineering" by Horowitz(sp) and Hill. read it - you might learn something from it about communication skill. If you cant help, dont hinder. Andrew VK3BFA. I |
Can I use a 120V Variac to get 220V?
And if you want to see a good textbook using this method, grab a copy of 'The Art of Engineering" by Horowitz(sp) and Hill. read it - you might learn something from it about communication skill. If you cant help, dont hinder. Andrew VK3BFA. Hi Andrew, don't you mean "grab a copy of 'The Art of Electronics' by Paul Horowitz and Winfield Hill"? As far as I can tell H & H never wrote 'The Art of Engineering'. You made some halfway good points in the age old "me Technician you Engineer" argument, but you lost credibility when you recommended a book that doesn't exsist. Attention to detail, Engineers do, Technicians don't :-). If you can't help, don't hinder. This had nothing to do with the orginal question-sorry. Gary N4AST |
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