Today I measured my mains voltage at 240+V.
My amp is built for 220V. It is an EL34 PP that uses 12ax7 and 12au7 on the input stage. I pulled out a pair of EL34 and measured the socket and found the unloaded heater secondary to be at 7.04V.
I don't know how high is the heater voltage if they are loaded, but theoretically a 6.3V windings would give about 6.87V.
I opened up the amp to see if there is any 230V or 240V primary windings. It does not appear to be the case.
I can't put my hand on the power transformer for more than a few seconds, my guess is it is around 70 deg C on the outside. Not great, but I guess it is not too much of a problem?
So tube life would be reduced at elevated heater voltage. My question is how significant is this? If it is something like 10-20%, I would think I can live with it. If it is something like 50% then I think have a problem.
If I were to get a 230->220V transformer, do I want EI or toroidal? What wattage do I shoot for? Amp is rated at 230W.
Thank you for reading.
My amp is built for 220V. It is an EL34 PP that uses 12ax7 and 12au7 on the input stage. I pulled out a pair of EL34 and measured the socket and found the unloaded heater secondary to be at 7.04V.
I don't know how high is the heater voltage if they are loaded, but theoretically a 6.3V windings would give about 6.87V.
I opened up the amp to see if there is any 230V or 240V primary windings. It does not appear to be the case.
I can't put my hand on the power transformer for more than a few seconds, my guess is it is around 70 deg C on the outside. Not great, but I guess it is not too much of a problem?
So tube life would be reduced at elevated heater voltage. My question is how significant is this? If it is something like 10-20%, I would think I can live with it. If it is something like 50% then I think have a problem.
If I were to get a 230->220V transformer, do I want EI or toroidal? What wattage do I shoot for? Amp is rated at 230W.
Thank you for reading.
You can just look for a bucking transformer. It does not need to be as large as the amplifier transformer.
For example, you need a 240 or so to 20 volt and use it to drop the mains by 20 volts. The secondary 20 volt side just needs to have the same current rating as the amplifier.
240 is probably pushing your transformer into saturation and causing a bit of heating.
For example, you need a 240 or so to 20 volt and use it to drop the mains by 20 volts. The secondary 20 volt side just needs to have the same current rating as the amplifier.
240 is probably pushing your transformer into saturation and causing a bit of heating.
You can build a bucking transformer, a simple small 220 > 12 Volt would do.
See elliotts article about howto :
Bucking Xfmrs
See elliotts article about howto :
Bucking Xfmrs
With my own power amps, I have watched that the amp is stable and within all voltage ratings up to 220V, but we have 235V AC. As I have a regulated AC power supply transformer (separate) I watched what happened to the voltages on tubes anodes and heaters when the amps are being supplied with those high mains voltage. My resume was, up to 220V the amp is all stable, but it drifts with only 15 Volts more AC towards the region where the power tubes anode voltage become critical, because the max. anode power dissipation is being more the tube should be applied to) and heater voltages rise to a value, that I wouldn't accept. With my regulated AC separate mains power, I now let the amp running on 200V AC and it feels pretty comfortable.
So beware on those high AC voltages, they could make your amp drift in territory, where not only tube life is greatly reduced, but safety is reduced too. Because when the total anode plate dissipation is more than max., the tube anode plate become too hot and it can begin to fade out very quickly.
Always watch and measure, with what voltage your amp can run on the values it has been desinged for. A little too much can be too much, if it was designed on the edge of its virtues.
Btw, my toroid main transformer is greatly over engineered, it just become hand warm all the time. If touching a transformer begins to hurt, something is under- estimated at the design to make it smaller or cheaper.
So beware on those high AC voltages, they could make your amp drift in territory, where not only tube life is greatly reduced, but safety is reduced too. Because when the total anode plate dissipation is more than max., the tube anode plate become too hot and it can begin to fade out very quickly.
Always watch and measure, with what voltage your amp can run on the values it has been desinged for. A little too much can be too much, if it was designed on the edge of its virtues.
Btw, my toroid main transformer is greatly over engineered, it just become hand warm all the time. If touching a transformer begins to hurt, something is under- estimated at the design to make it smaller or cheaper.
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Thanks guys for your inputs.
I was reading this old thread regarding the subject:
Heater Voltage Range, Hi or Low
I think this is a common problem. I don't think there is much risk of imminent meltdown, I am just wondering what is actual impact on tube life is like.
I measure the mains voltage with the thing that you plug into the wall to monitor power consumption, may not be the most accurate thing in the world. I did use it to read the consumption of the amp with music playing softly, it is 0.75A/180W. The declared power consumption of the amp is 230W. I can't play music loud at the moment, but I don't expect it to be much different. I also don't listen to music all that loud.
In the DIY world, we tend to use oversized transformer. But in commercial amps, this is often not the case, even some megabucks amps gets very hot. My Marantz AV receivers for example, if I were to open it up I don't think I can touch the transformers for long either. In retrospect, this might be why they get so warm.
I measured the tube socket with a very entry level Fluke DMM. I try not to poke around a live amp, but if my tubes die within 12 months I would investigate further.
A bucking transformer looks easy to implement and non invasive, might benefit my other equipment too.
I was reading this old thread regarding the subject:
Heater Voltage Range, Hi or Low
I think this is a common problem. I don't think there is much risk of imminent meltdown, I am just wondering what is actual impact on tube life is like.
I measure the mains voltage with the thing that you plug into the wall to monitor power consumption, may not be the most accurate thing in the world. I did use it to read the consumption of the amp with music playing softly, it is 0.75A/180W. The declared power consumption of the amp is 230W. I can't play music loud at the moment, but I don't expect it to be much different. I also don't listen to music all that loud.
In the DIY world, we tend to use oversized transformer. But in commercial amps, this is often not the case, even some megabucks amps gets very hot. My Marantz AV receivers for example, if I were to open it up I don't think I can touch the transformers for long either. In retrospect, this might be why they get so warm.
I measured the tube socket with a very entry level Fluke DMM. I try not to poke around a live amp, but if my tubes die within 12 months I would investigate further.
A bucking transformer looks easy to implement and non invasive, might benefit my other equipment too.
There have been statistical tests done back in the 1940's and 50's, if you were keen to progress your query about actual impact on tube life.
You say you made a heater voltage measurement, but then didn't identify the measured value or the meter (?)
How loud you play your amp doe not affect the mains voltage or your heater voltage, or in general your tube life.
You say you made a heater voltage measurement, but then didn't identify the measured value or the meter (?)
How loud you play your amp doe not affect the mains voltage or your heater voltage, or in general your tube life.
The tube life (heater) will be shortened. Heaters usually outlast their cathodes so I wouldn't worry about it. Also 70C isn't that hot IMHO. I have an amp (Class A MOSFET) that runs at 95C (chassis) and it doesn't seem to mind one bit. I have a Hammond 278CX that routinely runs at 95C and it's worked for years.
Koda
Koda
https://www.google.com/url?sa=t&rct...%20Tubes.pdf&usg=AOvVaw3OhYzRn2aOk8RUM9aM5FNw
In this article it tells everything affecting tube life and way to get most out of it.
In this article it tells everything affecting tube life and way to get most out of it.
Allowing the average voltage to run too high will reduce the lifetime of the valve - a needless waste.
The advice of NV Philips in the 1956 Technical review is the most useful: see attached. Much better to use a resistor to drop the voltage to the nominal (6.3V), or better still, stabilise the voltage to a value slightly lower than the nominal.
With Thoriated filamentary valves, run them with a stabilised voltage -5% of nominal, until the required anode current can't be supported (to due wear-out), then increase the voltage until the anode current can once again be supported.
The advice of NV Philips in the 1956 Technical review is the most useful: see attached. Much better to use a resistor to drop the voltage to the nominal (6.3V), or better still, stabilise the voltage to a value slightly lower than the nominal.
With Thoriated filamentary valves, run them with a stabilised voltage -5% of nominal, until the required anode current can't be supported (to due wear-out), then increase the voltage until the anode current can once again be supported.
Attachments
An overheated cathode may result in (very) high noise. It depends on the tube, but I experienced this recently when a 6SN7 got too much heater voltage. Noise was terrible so I shut down the amplifier immediately and there was no permanent damage.
If your mains get quite high, use a small series resistor in your heater wiring, to get 6.3 Volt. If the heater voltage sometimes is too low on other moments is no big problem; I’m more concerned about overheating.
Right now I’m regulating my 6SN7’s with DC 6.3V.
Regards, Gerrit
If your mains get quite high, use a small series resistor in your heater wiring, to get 6.3 Volt. If the heater voltage sometimes is too low on other moments is no big problem; I’m more concerned about overheating.
Right now I’m regulating my 6SN7’s with DC 6.3V.
Regards, Gerrit
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