Radio Transmitter High Voltage Transformer Repair/Replacement
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- เผยแพร่เมื่อ 8 ก.ย. 2024
- UPDATE: 11/26/2022 Power Transformer Replacement
It happened again and this time I gave up on using the transformer that I "floated" and replaced it with another large transformer. 3700 VAC into a SS bridge (Goodby beautiful MV rectifiers...). The original transformer arced again and I suppose went from secondary to case to primary. Time to recycle 50 pounds of copper and steel. Plate current "kick" is not present and it seems to be working perfectly with approximately 1400 watts PEP output.
UPDATE: 11/23/2022 Power Supply Modification
There were comments made about the plate current meter making a huge jump upscale to the right when plate voltage was removed. I agree that is a serious concern. I build an outboard box (no more room in the amplifier cabinet) where I mounted a 120K, 200 watt bleeder resistor and a 0.16 uF 8 KV capacitor connecting the capacitor across the 8H choke and the resistor to ground. This completely stabilized the amplifier with no more "kick" in plate current and the 4KV bleeds off in 20 seconds. I am not certain why this worked so well but it did solve the problem. I can only assume there must have been a momentary parasitic instability in the amplifier as high voltage was removed. Bias had to be raised more negative to about -110 volts to set the plate resting current at 50 mA. Furthermore, the orange spot in the plate of the tube went away without modulation and power output increased about 200 watts.
ORIGINAL MESSAGE:
I had a high voltage secondary winding short to the case in a high power RF amplifier power supply. The transformer was intended for a much lower voltage power supply, in the 750 to 800 volt range but I ran the output of 1800 VAC into a voltage doubler to 4000 volts. This 4KV is seen by the secondary winding and it finally shorted thru a dried and cracked insulator. Since I do not have or know where to get another transformer like I need, I did all I could to remove the short and then tested for any leakage between primary and secondary windings of the transformer to the case, which turned out OK but then insulated the metal case of the transformer so it would "float" above ground before reinstalling it in the amplifier.
Dave, you are right. Any voltage with three or more figures in it scares the bejesus out of me and I have to visit the bathroom before powering it up, but that's the way it's supposed to be. If you ain't scared you haven't figured the risks, and there's only one way that ends..
Very cool! I know exactly how you feel turning something like that on for the first time. I had a HV transformer sitting around for a while and just sold it not too long ago. It was 2kv @ 200ma . It was out of a 1kw transmitter.
I am regularly astounded by the parts you pull out of your inventory. You ever have a garage sale I'm flying down from Toronto!
Howdy! Heck I would go ahead and just pot it again in resin, those mica stands and a paint can or something similar:)
really cool! I have a x-ray unit power supply I will be tearing down soon. They are most definitely fun!
Do you know its voltage and current?
@@ElPasoTubeAmps It's a GE Dental X-ray power supply, don't know offhand the transformer output because I think it's using a multiplier after the xformer though not certain yet. Final output voltage has to reach 170KV to generate x-rays of equal eV. The current is little but serious voltage, wouldn't want that to go wrong. Will be peaking inside in the coming weeks or so and find out.
@@fjs1111 I have a nice collection of radioactive minerals that I collected several years back and the instruments to measure them. They were sold on Ebay at that time until the Fear Mongers terrified everyone with the word "radioactive". I am amazed we are still allowed sharp pencils - I know a lady a bit older than me that as a child had her right eye poked out by her sister and a pencil - accidentally... I assume you have some instruments to measure gamma. Sounds like fun... I always thought of mounting a microwave oven magnetron at the focus of a parabolic dish and seeing if I could bounce RF off the moon. Haven't done that yet. Maybe shoot down satellites with it also - just kidding... I did recently build a radio telescope and can easily detect the free resonate hydrogen in the galactic cloud around 1.21 GHz. I have also, with my grandson, made measurements at Trinity Site in New Mexico (and posted) where the first plutonium bomb was exploded (it was plutonium not uranium) and the site is still about 10x times more radioactive than areas away from there. Probably not very dangerous as long as you don't live there for years... Stay safe with that 170 KV... that would make you glow like a neon bulb. 🙂
You can try to find AC motor winding insulation testers, I have one of those with a hand crank and the dial goes up to 500Meg but it's not at all accurate up there. it measures at around 40V.
but I think a better way would be to use a capacitor leakage tester, with that you can often test at up to 600VDC, put it on the electrolytic setting because that's less sensitive (there would be some dielectric leakage anyway)
We could actually see initial capacitance leakage/charge between the secondary and case and between secondary and primary at 900 volts DC on a scale of 120 uA. It settled in at, for all realistic purposes, zero leakage. In any case it worked... maybe for a more sensitive measurement, a 20 uA meter movement could be used instead of the Triplett meter?
"Floating" components like transformers and chokes have always worked for me. I have wanted one of the hand crank meggers but the price on Ebay is way too much.
Electrolytic capacitors do leak, for sure, but as long as we don't exceed their voltage rating, they seem to be pretty stable for years. Running good quality electrolytic capacitors well below their maximum ratings seems to make them last decades and perform like new. Thanks for your comments and thoughts.
@@ElPasoTubeAmps you sure you don’t have one? I remember a video you did a little while ago with an old meter that put quite a high voltage you were charging up cap with it explaining how voltage increase’s even after discharging it! That was basically one. although it’s out put voltage was lower then the output of this transformer! The motor shop I worked at they used fluke meggers for like a quick basic test, “even if it test good it can still be bad” then the motors stator/rotor, or field frame an armature was pressure washed very well there can’t be any grease, or carbon dust, or even left over soap left inside. They were then baked for several hours at least 8 but some required longer. And then tested again, but with a Hi-Pot tester( still a megger, but can apply a very high voltage dc, and ac) I kinda knew how it worked it was made to test multiple types of devices motors, and transformer.
@@tucker934 It was actually this incidence that prompted me to get the megger. I have measured the short-circuit current on the megger and it is 1 mA which will keep if from being deadly but I am concerned about putting 5KV across small transformers. I don't know for sure if the HV could puncture the insulation but I assume it could and end up destroying an otherwise good component.
I remember the video charging up the caps. Pretty scarry... even though it can only pump 1 mA out, over time it can put a deadly charge on capacitors just as if they were connected to a high current supply.
Thanks for your comments. Stay safe.
@@ElPasoTubeAmps they wouldn’t use the max setting on the fluke megger, I asked one of the “mechanics” he stated with that device they will use it at a lower out put if the motor wasn’t a relatively high voltage, and they would like convert it, I think it’s for every one thousand volts, you need at least 1Meg of insulation resistance. I’m still relatively young, and new to the high voltage stuff. And yes that large cap you hit with that tester if I recall correctly it was around 5,000-6,000 volts, and it was very large capacitance! Very happy with the information I’ve gathered about capacitors! With the pieces of mica your using for extra insulation, there was a video on TH-cam that I’d watched it’s still up but quite challenging to find, this gentleman demonstrates how the change is stored in the dielectric it’s self, now I did believe it at that time I seen this, but much later when working at that motor shop, I was bead blasting (glass beads) some ceramic insulators that Inside of a plastic bucket, I thought I’d grounded it correctly to prevent the charge, I only grounded the outer portion that was already at ground silly me. After blasting I grabbed the outer most part of the bucket sat it on a table, and proceeded to remove one of the ceramic insulator’s from the bucket, there was still some blasting media inside the bucket but not much. In the process of reaching my hand in there just enough, there was a slight purple hue, then like multiple arcs coming from the insulators, and the blasting media. The only conductor that was on it was the metal handle on the out side. The shock I got, and arc I seen came from within the bucket from the glass beads, and insulators! I wonder if it’s possible to create like an unknowingly capacitor, by add extra insulation!
When I tried the transformer sitting on the floor, even at the lowest voltage taps, I was getting over 5000 volts and arcs. From my experience, most things below 3KV are not too hard to deal with as concerns arcing. At 4000 volts, it is a little more serious and layout and spacing becomes a bit more concerning. At 5000 volts, things are certainly different again and get pretty scary to me. A lot of thought needs to be put into a device running 5KV. I know people run 6000 volts on some 4-1000A amplifiers - I am not sure I want to be in the same room.... what is it about the sizzle of HV that we can love. Stay safe...
I worked at LADWP for a while in substations and receiving stations... our voltages are 4160 3ph. 210Kv 3ph, and the DC intertie is + and _ 500 KvDC to ground (1MEG VDC).
THAT has some sizzle!! Especially when the humidity is high! zzzzzzZZzzZZZzzzzz
@@pomonabill220 I have never worked around truly high voltage like you have. I was a computer geek and then manager. The highest voltage I ever dealt with was 208, 3-phase and we actually were not supposed to touch it but sometimes I had to do what it took to get going. I sometimes go shooting in the New Mexico desert under the very high tension lines straight from the power plant in El Paso that feeds the city of Las Cruces, NM. I don't know the voltage but they are sizzling and crackling all the time when under them. I kind of like but it also can make me nervous. I would assume it is something like 345 KV ??
@@ElPasoTubeAmps Well anything over 50V can be nasty and/or lethal!
@@pomonabill220 I believe I have read that any voltage that can drive as little as 80 mA thru our heart, usually from arm to arm, can cause fibrillation of the heart and do us in...
Why does the plate current spike when you release the key?
Beautiful setup of course!
I never noticed that before. Funny what I see in my own videos. I see it at 20 minutes into the video. I do have a 0.02uF capacitor across the meter. Maybe I need a larger one?
On the amplifier that sits on top of the 833A amp, I put regular 1N4007 diodes back-to-back across my meters just in case high voltage gets to the meter so it won't smoke it. The diodes, one facing one way and the other one facing the opposite direction, ensures the voltage across the meter can never exceed 0.7 volts. After watching this video, I noticed the glitch so I monitored the RF output signal on a scope and I see a very tiny glitch that I assume is the spike in plate current but it is very small compared to the RF envelope.
Maybe it is a power supply choke issue. When we charge a iron core choke by putting a battery across it, not much seems to happen as the magnetic field quickly builds up in the core of the choke but... when we take that battery voltage off, a truly huge voltage spike will occur across the choke from the collapsing magnetic field (with opposite polarity...) I have (carefully) measured a power supply choke (say, 10H) with only a 1.5 volt battery across it and get a 300 volt spike. There are warnings on GR inductance meters concerning the spike from the collapsing field of chokes being measured. At the moment I am thinking it might be something like this and if so, it surely is a multi-thousand volt spike possibly what caused the failure in the first place. I need to figure it out and fix whatever is causing it. Sorry for the babbling here... just thinking...
@@ElPasoTubeAmps could there be a delay in the relay keying and unkeying, causing this problem? 🤔 Would some type of sequencer circuit help? 🤔
@@ElPasoTubeAmps Yes. I cringed when that georgous meter pinned HARD!
I know what you mean about HUGE spikes from the collapsing magnetic field from any inductor... inductive kickback. The spike can be hundreds of volts for a few microseconds. But that can kill alot of things!
Even 0.7 volts across that meter is pretty big, but that is a common way to protect sensitive meter movements.
Just thinking here.... a couple of schottky diodes with 0.3 V drop back to back? Lower forward voltage drop, even though 0.3 volts is still high for an ammeter.
Would that offer a little more protection?
You are not babbling at all! I like reading what you have to say! I would be interested to see what you find and what you did to protect that beauty!
Stay safe!
@@ElPasoTubeAmps I would imagine if the spike is beefy enough, a cap might have to be pretty large to damp the spike out (or down to lower levels).
Probably difficult to measure the spike while in operation as that meter is on the plate B+ at 4Kv, correct?
A quick and dirty voltage divider would work... while STAYING SAFE or course. You are always very careful though! I wouldn't want to have to peal you off the wall! hehe
@@MM0IMC I see what you are saying, but depending on where he is measuring the current and where the meter is in the circuit, whenever the B+ is switched off, there is some inductance that is creating the huge spike.
I would be interested to see where the meter is myself.
Oh!!!! And cat fur conducts electricity!!! You prolly already know but not sure if others know that or not
High voltage rock n roll!!!!! Lol....my al82 runs 3.7kv......touch that plate cap and your day will go sideways!!!! It's not like holding a spark plug wire....it's dc AND has more than enough current to modify humans!!!
You can try a microwave transformer which are often 2100 volts.
I have a few microwave oven power transformers. One is quite large and I have taken the shunts out of some of them as suggested by some people to, if I understand it correctly, limit the current the transformer can draw thru the primary. I have not built with them yet but they surely are pretty powerful and no doubt deadly.
@@ElPasoTubeAmps I often used a ballast on the primary to limit the current.
These transformers are very strong and can deliver 3 amps for a short time.
According to TH-camr bigclivedotcom there have been 30 fatal incidents in the US with these transformers by people who did not know the danger they were facing
th-cam.com/video/FBeSKL9zVro/w-d-xo.html
@@20kilovolt That is very sad but does not surprise me.
𝚙𝚛𝚘𝚖𝚘𝚜𝚖 😀