One last comment on the MV rectifiers I forgot to mention. Besides not generating "hash", MV (Hg) rectifiers do not generate X-rays either. X-ray tubes run at voltage levels of 60 and 70KV just for small dental x-ray machines and at low current - like 8 or 10mA or so with pulses as short as 1 mS. I do believe mercury vapour lamps, as we see on the poles of our streets at night, do have a reasonable amount of UV output but... they are made from a (mercury arc) inside the lamp (current controlled by a series ballast) and run at very high temperatures (800 C, 1472 F) that are necessary for UV generation. The MV rectifiers as seen in this video do not run that hot simply because the voltage drop across them is so low - in the 15 volt range - multiply that voltage drop at even 500 mA and we get 7.5 watts of heat plus the filament heat and they actually run cooler than a 5U4 rectifier which can be at 450 degrees F. That doesn't mean you should touch MV rectifiers as they will be hot but not hot enough for the generation of UV light even though they are a high-purple colour. What temperature produces UV light? Medium-pressure UV lamps typically operate at a quartz tube surface temperature of approximately 900°C. The infrared delivered to a surface is primarily a function of the surface area of the bulb and follows the Stefan-Boltzmann Law.Sep 6, 2017
I sure was hoping that someone was going to make a great comment like this lol. I wouldn’t change the title, it’s great click-bait. One last thing, high voltage and high people Do Not Play well together!
Finally......... Someone who can give a definitive answer about mv valves. Over the past month I have been assembling a new amp I designed using Kt170 output valves. For fun I chose to go with a pair of NOS Amperex 866ax mv valves. All the tfmrs are shrouded and the ac part of the power supply is in a metal enclosure within the main chassis. I went ahead with the build in spite of all the "Don't do it" warnings. Mv holds a fascination for me. Thank you for this video... It puts all the fears to rest for me. I'm a week away from first power up and then into the tweaking if required.... Will let you know how it goes.
If my video has put to rest all this hysteria about "hash" and "x-rays" coming from Hg (MV) rectifiers, then it was time well spent on my part. I am sure you are going to love the look of those beautiful MV rectifiers. Please do let us know how your amplifier turns out. That is what this RU-vid community is all about. Stay safe...
Well since my last comment I am pleased to say that the new amp is up and running well after a bit of tweaking with the power supply. I did originally have a 10h choke as first load but it really made the choke buzz loudly. I ended up putting a 4uf film cap right on the high voltage pin of the rectifiers. 630v solen did the trick. After the choke it is 500vdc which is perfect for the rest of my design. Won't go into specifics. I can say that unless you put you ear right on the speaker there is no audible hum at all. Can I send you a photo somehow? The mv tubes really light up but I'm not sure if it's normal or not. Your experience will help here. Regards, Trev.
@@ElPasoTubeAmps Forgot to mention that I have a 4 minute warm up delay relay for the mv tubes. When the relay closes it grounds the centre tap of the heater circuit thru a thermistor so the surge into the first cap is controlled.
@@NZkiwibandit Hi Trev, In low voltage tubes like the 83, the blue is there but not too bright. In my KW RF amplifier the 866A are nice and bright so I think your case is normal. As for noise out of an amplifier, I have found that anything better than about -75 dB S/N is perfectly quiet out of very efficient speakers. Many amplifiers state -90 dB and it may be true but it isn't necessary for a very quiet amplifier. My RU-vid direct email is theaudioshop@sbcglobal.net if you want to send pictures.
@@NZkiwibandit I need to put in a delay-relay circuit in my Heathkit 807 amplifier since I put in the 83 rectifier. It pops a little on warm up and I figure (but I am not sure) it is the MV rectifier. Stay safe...
You indirectly mentioned that Hg vapor rectifiers are quite efficient. Besides the potential toxicity only the long warm up time seems to deter would-be users.
I installed a 811 on my HH Scott 222c but I have to slowly bring up the ac with a variac but it sounds great I made a adapter for it it does flicker when volume is increased
There is that warm-up issue with MV rectifiers and all of my equipment that use these rectifiers have a switch to enable/disable HV to give the rectifiers a couple of minutes to warm up. As some people state correctly, if the Hg rectifiers have not been in an upright position and initially given maybe 30 minutes to get-in-shape - that part is necessary for some just out of the box and storage - but after they have gone thru that initial settling-in period, it only takes 2-3 minutes for the filaments to warm up once the Hg is properly conditioned to apply HV. Three minutes is all Collins transmitters give the rectifiers to warm up and then apply over 6KV AC across the two rectifiers for 3KV DC output from a choke input filter. I apply 1800 VAC from a 1A transformer across the 866A that you saw modulating with just a couple minutes of warm up time - they are in a voltage doubler and with the capacitors, end up at 4KV. I forgot to mention that no one recommends Hg rectifiers be used into a capacitor input filter but with a voltage-doubler, there is no way to prevent it as that is the way a doubler is built but mine have been operating for years with that initial surge current to charge the capacitors. Honestly, I am a bit surprised it has not damaged my rectifiers over the years but it seems they are tougher than we think - thanks for your comments. Stay safe...
I love the look of the Hg rectifiers as well. People put blue LED's under their tubes to simulate the effect but to me that just looks trashy. There's nothing like the look of the real ones in action.
I have a few mercury vapour rectifiers which I've thought of using in an amp PSU, problem is there's not too many of them about in the UK at least at reasonable prices, meaning if in the future they need changing and there's non to be had the PSU design is redundant. There is a bit of hysteria too because they have mercury in them, so, great valves but only for specialist/occasional use.
I understand that and do not build with tubes I only have one or two of and are hard to find. On the other hand, if you build with the MV rectifiers you can always go to solid state diodes and keep the equipment running. Fear, confusion and misinformation rules the Internet about things like mercury and asbestos - if you even look at either, everyone will die... I like some of the statements I read today - one was: "we don't have rules here - we are trying to solve problems", and the other was: "we don't look for problems, we look for solutions". I know that is old-school thinking and will surely be burned-at-the-stake today in modern media but it is kind of how I look at things. I do plenty of (perfectly legal) things that people just don't get but it is OK... Lastly, MV (Hg) rectifiers are, as you say, speciality items only for a few.
@@ElPasoTubeAmps Completely agree: we used to play with mercury at school when I was a kid back in the late 70's and I have several big mercury tilt switches near my bench on the wall. One last thing, I've found the MVR's I have tested don't glow much, maybe because they aren't running at a high enough current or voltage. As audio amps only run at 2-300mV tops this another reason I' haven't used them. Great video BTW, have missed your amp builds this year.
There is a video on youtube that shows a 1Kw audio am that uses (I think) 6 Hg rectifiers playing organ music at full output, and those tubes just "dance"! Of course the whole amp uses tubes with a huge output transformer! here is the video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-G7qMVYf85sM.html YEAH BABY!
I have watched that video a few times and never thought of using it as a perfect demonstration of how MV rectifiers are perfectly fine for audio - thank you - I am sure others will enjoy it also.
I came here for the free mercury vape hash....seriously though, I've always wanted to build an amp with 872s in it. They look absolutely gorgeous when operating. BTW, what was that "spark" at about 7:50 near the MV tubes? Thanks!!
That flash is "normal" on that amplifier as it does it most every time. I assume it it the surge current drawn to charge the capacitors in the voltage doubler arrangement. Apparently, I lucked-out and the capacitors are not too large to damage the tube but high enough to cause that extra flash when the HV is turned on. Some people turn the HV on and leave it on and bias the tube off/on but I turn on and off the HV each time I transmit and stop transmitting. I use a solid-state relay in that particular amplifier in the HV transformer primary so I don't hear that loud clank of a mechanical relay. The unfortunate thing about SS relays is if a HV short occurs, it almost always shorts the SS relay from huge over current thru the primary. The relay is rated a 60A.
Great Video, I love the color of the Hg Vapor Rectifiers! You speak about "Hash", what exactly is meant with "Hash" ? Hum, HF Noise(like from a SMPS PSU)?, White noise ?
That is a good question and I do not know the exact definition (sound) of "hash". I would assume it is some undesirable noise created in the power supply that is induced in the output of the amplifier (most likely AM transmitter) like you mention. What exactly it sounds like I do not know. What prompted this video is that word "hash" gets thrown out so often in comments and blogs whenever someone asks about using Hg rectifiers and I know it is not true. The Hg rectifier has been blamed for "hash" for the last 100 years and it would only occur, as clearly stated in the manuals, if the rectifiers are in a strong RF or magnetic field that can ionise the Hg between the cathode and plate during operation of the rectifiers. "Hash-filters" as they were called long ago, were simple RF chokes added to the plate leads of the tubes to help keep RF out of the tube. Hg (or MV) rectifiers are used in the old high-end vacuum tube testers (TV-7 type) because of the constant voltage drop and certainly there could be no electrical noise permitted in those instruments. It seems at low voltage, i.e. in a tube tester, it is OK to put plate voltage on the rectifier before it warms up and no harm is done. I know that can not be done at thousands of volts without damaging the rectifier as it must be at operating temperature before HV is applied to its plates. That in itself would make it necessary to have a HV on/off switch on an audio amplifier or a delay-relay of about three (3) minutes to allow the filament to come up to operating temperature. But everyone agrees they are beautiful and we still like them and use them regardless of their size and filament requirements.
Thankyou for the Honest explanation, I am not a Ham but I love Tubes since I was a Kid in the 70's when I was Building Pirate AM & FM Radio Transmitters in Greece. Tubes in General have something Mesmerizing :-), Cheers, Konstantin
Great video! I have been thinking about building an audio amp with mercury vapor rectifiers. I heard that they give off X-rays, is there any truth to that?
As Bill states above - only at very high voltages do we get x-rays. Next time you go to the dentist, see if you can find the specification plate on their x-ray machine that lists the voltage and current. Here is a little data I found that might be of interest about dental x-ray machines. 4. Specifications： 4.1 Tube voltage：60/70kVp 4.2 Tube current：8mA 4.3 Power: 0.339kW 4.4 Earth Leakage Current Normal state：≤0.5 mA Single failure state≤1 mA
Here is the basic article. www.arizona-am.net/PHOENIX/NA7RH/ARRL%201625%20Mod.pdf Another great article - worldradiohistory.com/Archive-DX/73-magazine/73-magazine-1961/73-magazine-09-september-1961.pdf
@@ElPasoTubeAmps Thank you! Interesting, did you use the interstage transformers or switch to resistance coupled? This looks like an article that would have been in the Radio Electronics Magazines from the 50’s. I have found a wealth of information in those! Love your channel!
Yes, these days they can be substituted with solid state devices, as can high output final stages of amps both RF and AF, but where is the romance in that........if you can't see the beauty in the glow of any valve be it a MVR or a Big final stage glass Tube, well maybe you are a solid state guy or gal..........Valves of all types , other than the steel or ceramic ones have an aesthetic value that just can't be replicated in any other way.......and that justifies any cost or danger they may inflict on a project...........and for the record, any person I have brought in for a TX site tour never sits mesmerised looking at a bank of Transistors like they do looking through the inspection window of a large Valve based Transmitter at full power.
What about UV light? I have read that the mercury vapor tubes emits at least some UV light. But the glass bulb filters most of the harmful wavelengths out. But there seems to be a lot of different opinions out there about this ass well. I'm not too worried about it personally but it would be nice to know. I guess it could be measured if you had the right equipment.
I do not know an absolute answer to the UV question. Some people state it like they know what they are talking about but provide no proof. Declarations and opinions, not scientific proof, seems to rule Internet knowledge and wisdom. I did try my best to answer it below and your comment about the glass filtering adds to my belief that there is nothing to worry about. So I don't repeat myself, my thoughts on UV are in my comment that starts with: "One last comment on the MV rectifiers I forgot to mention". As soon as that question was asked the first time, I started researching UV measuring equipment - but... we have UV-A, UV-B and UV-C which will make the answer to all this go on for ever and cost $$$$$. I am not worried about it either.
@@ElPasoTubeAmps You can check for UVC with a $10 Quantadose UV test card. It will glow in the presence of UVC light and change color to give a rough approximation of the amount of UV light it's exposed to. UVC emission shouldn't be a problem since glass blocks it though.
