30-400V Tube power supply with three PL500 - Page 1
Forum section: electronics / projects

author: Rbastler
author_rank: Frequent Contributor
timestamp: August 21, 2016, 06:23:14 pm
content: I already had a tube power supply, but that was much bigger an had a very big issue. Therefore I decided to build a new one. It has lower functionality, but all the problems of the previous one are solved.My old PSU had also a output for negative voltages. Mainly to provide tubes with a grid voltage, if necessary. I taught that this is a bit overkill, since the negative part could supply up to -350V and 100mA.A small semiconductor supply capable of -50V and 30mA is more than enough for the grid voltage supply of tubes. I have that on my to do list. Since the negative part is now missing and some tubes were substituted by semiconductors, I managed to fit the power supply in a much smaller caseNow to the biggest problem of the old power supply: When switched on, the main rectifier tubes and regulator tubes, heated up before the reference voltage supply. Because of that, the output went up to maximum voltage ! When the reference voltage was there, it turned back to were it is supposed to be. When switching off, the reference voltage fell faster than the main voltage, therefore and because the main regulator tubes were still hot, the voltage jumped up to maximum again ! A very dangerous problem, which I solved in the new version by putting a HGTG20N60B3D in series with the output. When the supply is switched on, the IGBT is turned on. When, its off, the IGBT is also off. That way I resolved the problem with having a massive overshoot at the output, when switching off.When switching on, there is no problem either, because I use Zener diodes, instead of gas discharge stabilizers.The schematic I used is from "Jogis Röhrenbude":http://www.jogis-roehrenbude.de/Bastelschule/Funkschau-Netzgeraet.htm. I modified it to fit my needs.As display I used a 1602A display driven by a Atmega8. A LM358 amplifies the voltage drop across the 10Ohm shunt to 5V, as I choose 5V to be the reference voltage of the Atmega8 ADC.I added a inrush current limiter too.Where necessary I used the Dremel to cut the copper away for isolation, since I have up to 800V difference in some parts of the board. The reference voltage is negative. That's why I have such a large voltage difference in some parts.https://www.fairchildsemi.com/datasheets/HG/HGTG20N60B3D.pdf

author: oldway
author_rank: Super Contributor
timestamp: August 21, 2016, 08:23:46 pm
content: If I had to design such a HV power supply, I would choose other technical solutions:Here some ideas....- HV transformer would have a triac phase control pre-regulator to limit dissipation of the series regulator tubes.Only one range from 0 to 400Vdc.Power HV transformer is than an easily available isolation transformer EREA 400-220V/110V + 110V using the 110 + 110V as primary and 400V as secondary + bridge rectifier.No problem of inrush current nor overvoltage as the preregulator is only enable (with soft start) when all tubes are running hot.- I would choose PL or EL 519 as series regulator- I would provide adjustable current limitation.- reference would be only semi-conductors (TL431 for exemple), no gas discharge stabilizer.- No IGBT, nor Mosfet.- SCR crow bar protection in case of arcing in series regulator tubes.

author: Rbastler
author_rank: Frequent Contributor
timestamp: August 22, 2016, 03:02:17 pm
content: Quote from: oldway on August 21, 2016, 08:23:46 pmA adjustable current limitation and a crowbar would indeed be good to have in such a power supply. But since my "design" was based on the schematic from Jogis Röhrenbude, I didn't really knew how to implement the current proptection, so I left that away.I agree using P/EL519 would be better too. Since they are quite expensive and I already had the PL500, I used those. I wanted to build the supply with parts I had at home, not needing to buy something.Would it be good to use a active rectifier with mosfet or SCR instead of the triac regulator ?As reference I'm using six 47V Zener diodes, since gas discharge stabilazier are too large.

author: oldway
author_rank: Super Contributor
timestamp: August 22, 2016, 05:25:11 pm
content: Some others valve regulated HV power supplies:MBLE BED002 0 to 350V 100mALAMBDA Model 71 0 to 500V 200 mAHP711A 0 to 500V 100 mAVAN DER HEEM Model 8619 0 to 350V 150 mAIP32, IP17, IP2717 HEATHKIT 0 to 400V 100 mAPHILIPS PE4832 0 to 500V 600 mAAnd a modern one:POWER DESIGNS Model HV-1544 1 to 3000V 20 mA.EDIT: also KEPCO HYBRID power supplies.

author: calexanian
author_rank: Super Contributor
timestamp: August 23, 2016, 02:43:04 am
content: That is a pretty tried and true series pass parallel tube regulator configuration. It will pump out the heat, but tried and true.I see no problem here. Carry on.

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 23, 2016, 05:24:26 pm
content: Gas tubes provide far superior regulation than jellybean zeners, especially stringing them together. If you absolutetely must use zeners you should use temperature resistant zeners otherwise you'll get massive drift near hot tubes.

author: oldway
author_rank: Super Contributor
timestamp: August 23, 2016, 06:11:35 pm
content: In the 70's, I was developping and manufacturing tube amplifiers as hobby. (Guitar and Hi-Fi amplifiers)I have never needed a stabilized HV power supply because my amplifiers did not had a stabilized power supply and I wanted to test my circuits in the same conditions that those they would be used.My ajustable power supply was simply a tranformer with a lot of taps and two commutators to choose them.There was a bridge rectifier (silicon diodes BY100) , a high voltage capacitor, a big inductance and a second HV capacitor.The power supply was protected by 2 fuses in ac inputs of the bridge rectifier.There was an analog voltmeter and an analog milliamperemeter to read output voltage and current (up to 300 mA).As you see, very simple indeed ....

author: Rbastler
author_rank: Frequent Contributor
timestamp: August 23, 2016, 06:52:44 pm
content: Quote from: Cyberdragon on August 23, 2016, 05:24:26 pmThe Zener diodes are on the opposite side of the board, a bit away from the tubes. I used 1N5368A 47V/5W diodes. I dindn't used gas stabilizers, because I didn't have the space. Good to know, that in that case gas tubes are better.QuoteI build this power supply for the same reason somebody needs any lab power supply.

author: oldway
author_rank: Super Contributor
timestamp: August 23, 2016, 07:42:55 pm
content: Modern electronics has tight requirements and need stabilized power supplies.Electron tube technology not at all.Everything changes during working, cathode temperature, caracteristics of the tube, this is why an electron tube circuit must be very tolerant about his power supply.They generally don't need stabilized power supplies.

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 23, 2016, 09:50:48 pm
content: Quote from: oldway on August 23, 2016, 07:42:55 pmEntirely depends on the device, either tube or solid state, whether it needs regulated power. A simple radio or amplifier doesn't need regulation. But alot of tube communication equipment, high-end test gear, radar, and televisions have regulated supplies. The old Tektronics scopes not only regulated every DC voltage but used a variable saturation transformer to regulate the line voltage and control the heater voltages. Also, the characteristics only change as they are warming up, transistors will do the same thing when they get warm. Once the temperature is stable everything else will be.

author: Rbastler
author_rank: Frequent Contributor
timestamp: August 24, 2016, 05:08:44 pm
content: I just didn't want to build a entire new power supply for a tube project every time. Therefore I build this stabilized power supply with a wide voltage range.I have attached photos of the modified schematic and the place were the zener diodes are on the board. They shouldn't get much heat.edit: I forgot to add the voltage divider(100:1) and the current shunt(10Ohm 2W) to the schematic.