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Technical Bulletin TB-04

Written by: Jac van de walle

Upload06-Aug-2017e -->

Today, the mains voltage has become unreliable. It is changing up and down randomly 10% in some countries, due to communities giving that part of the responsibility to the electricity companies. This can be so for any city, and any part of the world you live in. There are moments when the voltage is correct, and suddenly it can be up or down 5...10% for just some minutes or hours. However, there are many tube amplifiers out in the field, which can do maximum 5%. Problems are huge, and your equipment can be damaged when it is not build for 10% mains voltage tolerance. Also, the normal, defined voltage, has been secretly raised. Electricity companies have their reasons, but it came uncommunicated, and this process still continues everywhere.


In the early days of AC electricity, the voltage was changing 10% or more. In 1920, radio tubes had only 500 use hours. So you would care extremely for lifetime. The simplest solution was, each tube had it's own adjustable series resistor in the heater circuit, and before you operated your radio, you had to adjust this, so each tube was heated at the correct voltage. Later, first commercial radios had huge cabinets, and inside was room enough to use a so called ballast tube. There are interesting NOS supplies of that sill, as today nobody wants to use them. A ballast tube looks very much like an incandescent lamp. So it has only two connections, and a glowing wire inside. The electrical behavior however is like a constance current user. So no matter what voltage you apply, the current is always the same. Suppose you have a 600mA type, the voltage can vary from (say) 10 to 20 Volts, and there is always 600mA current. Older tube tester had often settings to test those. At lower voltage than 10V, the lamps stops 'burning' and it becomes a plain resistor, so it looses it's function. Above 20Volts, the lamp burns too bright, and the heater can break. So the voltage range is limited from 10...20V, but that is enough and just what we need. If such a device is put in series with a tube radio, this will allow for 20-10 = 10Volts variation of the mains voltage, and still your radio sees always the same voltage. Effectively, the mains voltage variation would be over the ballast tube. So the small investment in the ballast tube will pay off, as your radio tubes last longer. However with the increasing quality of the mains voltage, these devices were forgotten.

Period from 1960....1995

During this half decade, the mains voltage was a stabile factor. When you had 220Volt AC, you could plug in a voltmeter, any time of the day, and it would read 220Volt.

Period from 1995 until today

Quality of the electricity networks was going down, because communities had the glorious idea to sell their networks to the electricity companies. Of course things came, as it had to come. Electricity companies would charge for this, and not maintain the network, so to get more profit. So now we are stuck with badly maintained networks, from the 1990's and also their size not adapted to the needs of today. This can lead to a total network collapse. So randomly, cities or whole regions can be without electricity. What makes things worse is the growth of the solar panel market. So all of those solar panels are feeding energy into the system locally, and in the block where you live, during sunshine hours, voltage suddenly can rise 5 or 10 Volts. The same can be so during 'wind' periods, when you live near by wind powered generators, specially at periods of low electricity use. Then, regions or whole countries are exporting or importing electricity nowadays, and we all know, the only was to make current flow, is a voltage difference. So here we go again.

The next thing is, the electricity companies do not like the energy loss in the cabling BEFORE your electricity meter, as they have to pay for this, instead of you. One solution can be to make those cables thicker, but that means investing in the network, and they don't do that as a matter of principle. A cheaper way is, to increase the mains voltage. Since power loss is proportional to the square of the current, that give a nice possibility. A higher voltage means lower current use. That saves money, it is as simple as that. This increase is done secretly and slowly over a period of many years, but we talk about 8...10% ever since. There seems to be no master plan, and no rules. So the direction for the future is: upwards. What was 220 Volts in 1995, can be 240Volts in 2020.

Possible problems and effects on equipment

  1. class="Standard-Text">The transformer mains voltage. Check on the back of your equipment, for what mains voltage it us build. You may read there: 220 Volts for amplifiers from the 1980's. Now measure your mains voltage, and you may find already 238 Volts at some moments. When you over dimension a mains transformer, the iron and copper volume, so cost and weight, go up in the same ratio. So, suppose it was over dimensioned 10% (which is unusually high) this transformer can be used up to 232 Volts only. Right above, it begins to heat up the core SIGNIFICANTLY, and some transformers become loud, and produce a bad looking wave shape at the secondary. Interestingly, the saturation helps to keep the voltage at the secondary side down, but this sure is no good thing to do. You can NOT connect 220Volt equipment any more to today's 230 Volt mains voltage, and in a few years we will be seeing effectively 240Vols anyway. Some older equipment, has the option to choose between 220 or 240Volts. Really I have NO IDEA why people do this, but they prefer 220V in that case. This is WRONG. 240V is sure the better setting today. A similar situation applies for 110 or 115V. Here, it pays off even more for the electricity companies to secretly increase your mains voltage. First, this will increase the electricity they sell. But second, at 115 Volt, the power loss of the cabling to your house is higher as with 230Volts.So they will try to increase, already just for that second reason.
  2. Tube heater voltage. Many electron tubes have maximum 5% tolerance on the heater voltage, whereas maximum lifetime is only reached at zero percent deviation.


  1. class="Standard-Text">A very good device, is a voltage stabilizing transformer. These can be found on Ebay cheap, as many were made, and most people don't know what this is. The disadvantage is, the are a bit noisy. So for HiFi you need to build a cabinet around them. Yet these work very good, and are automatic, and no calibration. Take care, most are for 220V or 110V output, so not 230V, or 115V. So you need a small 230 to 12V (5A) transformer in series, to create 232V / 5Amps.
  2. class="Standard-Text">Electronic controlled stabilizing transformer.
  3. class="Standard-Text">Variac. Use one with a clear voltage indicator. Such are low cost, but you do need to keep an eye on the voltage, as it can change suddenly. For 70 Euro you have a new made Variac on Ebay.
  4. class="Standard-Text">Automatic, motor controlled Variac. Expensive but nice.
  5. class="Standard-Text">Use electronically stabilized circuits, but at EML we only give guarantee on the tubes when approved modules are used.

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