Making Due with out an Amperage Meter?

[ElectronTubesRule]

Ok I want to figure out what type of current rating I have from my transformer's. I was thinking I could simply keep adding in resistors as a load until I see the voltage out put fluctuate then multiply that figure by .707 to figure out what I have as an RMS or CCS current for that voltage output. WIll this work to get me in the ball park so I know what I have to work with?????


Not going to lie I have not touched a circuit since 1993 when I gave up an electronic apprenticeship to pursue college in non-Electronic major!

I picked up an ARRL Guide Book and ELectronics for Dummies as refresher's....LOL

Also has anyone used a reformer or built one to reform old electrolytic caps??? I have read about them long time ago but never used on or done it.

Oh I bought some un-none high voltage transformer's. All I know is that they used to be used to run larger sweep tube amps that typically had 2 driver's and 4-6 final tube's. They are strictly high voltage transformer's with no taps at all for the low voltage stuff.......I will test them this weekend if I have the time.I bought 2 of them and will probably by 2 more. I am hoping that 2 of them will give me 2000-2500 volts and .600-.800 amps when used in some combo of series or paralleled. Depending on what I find I might use 3-4 of them to build a high voltage test supply so I can build an RF Deck separate of any power deck. This would allow me to build/play around with many different project's at a lower total cost. Only ordering a power transformer once I had the design of the RF deck sorted out. So if I go that route I will probably use 4 of them so I know I will have at least 4000 VOlts at 1 to 2 amp CCS to play with.

I need to find Orr's book.

 

[Kamikaze]

Some older Orr radio handbooks are available for free download.

The Radio Handbook 15th edition | Free eBooks Download - EBOOKEE!

Reforming capacitors can be done with any HV supply hooked to a variac. Ramp up to working voltage slowly and watch current. Any heating means the ramp is too fast.

Caps that have been turned on in a circuit after extended non-use may be damaged.

Caps used in voltage multipliers are not good candidates for re-forming.

Variac-ing entire pieces of equipment with the hope of re-forming caps causes more damage than just powering them up.

Be wary when trying to series up high voltage secondary windings. The working voltage of the windings can be exceeded and the xfmr will zorch.

 

[wavrider]

Power Transformer Capabilities

For what it is worth here is a link for amperage per weight for transformers.

 

[linearone]

if the cap works good, dont mess with it. If its leaking or you hear noise just replace it.

 

[ElectronTubesRule]

Well I have some 450V caps but the original design used 500V Electrolytic caps. I do not have any 100V or even 50V caps to put in series. I was hoping to reform new 450V caps with a surge rating of 500V to work properly at 500V's. The original circuit used 10mfd 500V caps. I have 100mfd 450V caps on hand. I already am grossly exceeding the 80% rule ont he capatence side of things. So I would prefer not to have to buy more 450V caps at a lower rating and need to put in 100V cap in series to bring the entire thing up to 500V. I can I was just looking for another solution. I hateing buying more cap's for something like this because if you have nothing else to order at the time the shipping kills you!!! I will just have to wait longer to get the unit on the air.

The problem is that the Corneil(sp) Dublier Paper Cans are huge and they have fuzzy paper blister's on the end caps. So even though the unit powers up fine and work's it is only a matter of time before these two 500V 10mfd caps go bad. They are int he main power section just before the voltage rectifier card so kind of important caps to have functioning properly! I do not think it would take out the tubes if one of them died since their are caps after them and a boat load of diodes but I prefer not to risk it!

Thanks for the link and the advice. At this point I remember just enough to be dangerous....LOL

 

[wavrider]

Many parts suppliers still cary the 500v caps, sort of expensive though.

If the circuit is not frequency sensitive go with a higher MF cap and call it done.

Electrolytic have progressed so much in the last couple decades that now they are very small yet function as good as if not better than the old huge paper caps of yesteryear.

HD Electrolytic Filter Capacitors at RF Parts Company

30UF 500V Little extra filtering never hurt anything.

good luck on the project

 

[ElectronTubesRule]

Thanks for the info. I have seen some 500V caps and they where pricey so when the Electronic shop told me they where not made any more I had questions. I also woundered if they where NOS caps.



So can anyone point me to the reason why series wired transformers can run away? Is it an inductance issue???? I know I could do it with isolation transformers but I can not imagine what something with enough current handling would cost so I am not considering that at all.

I am though considering that you are 100% correct though. So would it be better to wire then parallel for max current capacity then use a voltage multiplier to get to the voltage I want???? Would it be best to build multiple voltage boards or multiple units?

 

[Captain Kilowatt]

Be wary when trying to series up high voltage secondary windings. The working voltage of the windings can be exceeded and the xfmr will zorch.

True. Some guys have insulated the transformer from the chassis and that solves the problem of a case to ground short from happening if the insulation breakdown voltage is exceeded. That also may present a safety issue however by connecting the transformer case to ground thru a small low current fuse (one amp is great) it will serve an an indicator if the transformer has flashed over. I had to do that one time to a modulation transformer in a broadcast transmitter to prove or disprove that the transformer was breaking down under some conditions of modulation.

So can anyone point me to the reason why series wired transformers can run away? Is it an inductance issue???? I know I could do it with isolation transformers but I can not imagine what something with enough current handling would cost so I am not considering that at all.

They don't run away. The insulation breaks down due to the higher voltage applied to them.

 

[wavrider]

True. Some guys have insulated the transformer from the chassis and that solves the problem of a case to ground short from happening if the insulation breakdown voltage is exceeded. That also may present a safety issue however by connecting the transformer case to ground thru a small low current fuse (one amp is great) it will serve an an indicator if the transformer has flashed over. I had to do that one time to a modulation transformer in a broadcast transmitter to prove or disprove that the transformer was breaking down under some conditions of modulation.
.

CK I have been reading about that same type of isolation using microwave oven transformers as PS, Having to isolate the TR from ground due to the way the TR is constructed.

 

[Captain Kilowatt]

CK I have been reading about that same type of isolation using microwave oven transformers as PS, Having to isolate the TR from ground due to the way the TR is constructed.

The microwave oven transformer has one side of the AC line connected to the case which is a different sort of thing but essentially is an example of a turn shorted to the case when two are used in series. An alternate is to use two microwave oven transformers in series with the cases grounded and use a conventional full wave rectifier instead of a bridge rectifier.


http://www.kronjaeger.com/hv/hv/src/mot/index.html

 

[ElectronTubesRule]

MOT transformer's are designed kind of like HV Neon Tube Transformers. That is to say that they take the center tap most of us would use for power supply and they ground it to the case. They do this to limit how much current the transformer can attempt to put it in a dead short type of situation. It acts to limit current flow past the design limits of the MOT. In a Microwave they run the power output to a decent sized cap then dump it right into the magnatron with no current limiting and other then a diode burried in the cap nothing we would call rectification either very dirty design. To keep the magnatron from drawing more current then they want and burning out the MOT they take the center tap and run it to the transformer case then ground the case to the chasis.

So the above is why we need two of them preferable after their magnetic shunt has been removed in series so you can use cheaper full wave rectifier circuit design.

For th record is you want to have 6.3 volt for filliment after you dock out the shunts their is enough space to take insulated wire and wind two transformer's for 6.3 volts. Usually a 1 turn for 1 volt ratio applies so you can make 7 turns and end up with about 6.6-6.8 volts. You can also do 4 wraps then wire the two filiments winding in series. Not at all hard to get the 7.3-7.8 volts down to 6.3 once you pass it through your rectifer board. A simple resistor could be inserted if you did not want a complicated voltage regulator circuit to get you to 6.3 in an almost idiot proof and bullet proof manner. The diamter of the wire is what controls current so you could use some very large wire since you only need to get 4 turns on each of the 2 MOT's.

I currently have two very nice HV transformer's to use for my project but I also have two MOT's that I will eventually use in a project. I think though that it goes with out saying that if you are going to use MOT's expect to spend more on your caps and diodes to ensure insanely stable, clean,stiff power supply to your rig. The huge sum of money you are saving on the transformer more then offset's the increase in capacitor and diode cost.

For the record anyone that wants to use matching transformer's to make wiring more stable for series work should consider ebay. I have seen brand new MOT's for $11 each and $17 to ship them. That would allow you to use identical transformer's so draw and output when wired in series would be close to identical. I think you will find almost all MOT's will be 2100V under load and about 2500 with no load. The difference from one to the next will be based on the output power of the Magnatron in the unit which will make the current output from one MOT to the next differ if they are from different power output microwaves.

I know I left something out but I think I got most of it.

 

[wavrider]

CK thanks for the link good reading.

ETR, ( Electron Tubes Rule) thanks for the explanation, I have access to a lot of MOT to play with, no cost and have enough spare parts in the junk drawer to build a few GG triode tube amps, 3-500Z, 572B's and the filament tr to light them up. The MOT would be a cheap B+ supply.

 

[ElectronTubesRule]

I understand. My Mom and Dad moved a few years back and with out asking me they sold all of my old "junk to them" or pitched.

For instance I used to race imports in High School and did a lot of Four Wheeling. They sold multiple engines I had race preped and totally rebuilt for $200 sold manual transmissions for $200 and pitched all my electronic parts. So my life time of toys and parts are now at ZERO and I am starting over again! I used to save Transformers when ever I came across them not so much because I planed on doing this but I know how expensive they can be and when you need one nothing else will do!

The Boy Racer in me almost cried when I heard what they had done! Back then I was aprenticing to become an Electronic Repair Tech and maybe go to college for something inthat field! So I had access to all kinds of close to free goodies that you just do not get if you are not in the right place at the right time!

So I envy your parts inventory! Do have fun....It will take me a while but I am enjoying the process.