I'm writing to get a sense of how dangerous it is (shock) to build an SET power amp? I'm very interested in undertaking this project but will forgo it if shock/electrocute risk is prohibitive.
I have some soldering experience - resistors in my phone pre, driver in a speaker, switch in a pre, but my question is, can I take some reasonable steps so building an SET is a safe project, or will there always be a risk that I do something accidental or stupid and get zapped?
Thanks,
Robert
I have some soldering experience - resistors in my phone pre, driver in a speaker, switch in a pre, but my question is, can I take some reasonable steps so building an SET is a safe project, or will there always be a risk that I do something accidental or stupid and get zapped?
Thanks,
Robert
Hi, I don't know if you have seen this "Sticky Thread" at the start of the Tubes / Valves Forum, but there is good info on this there.
http://www.diyaudio.com/forums/tubes-valves/30172-safety-practices-general-ultra-high-voltage.html
Building tube amps isn't dangerous, per se, it's the builder's absent mindedness that gets him into trouble and zapped. The best rule to use (it's akward though) is the "one handed rule". When you have the amp powered up and are working on it, you have one hand deep in your pants pocket and only work on the amp with the other hand. This prevents the HV from going from one hand to the other (and through your chest / heart).
Daniel
http://www.diyaudio.com/forums/tubes-valves/30172-safety-practices-general-ultra-high-voltage.html
Building tube amps isn't dangerous, per se, it's the builder's absent mindedness that gets him into trouble and zapped. The best rule to use (it's akward though) is the "one handed rule". When you have the amp powered up and are working on it, you have one hand deep in your pants pocket and only work on the amp with the other hand. This prevents the HV from going from one hand to the other (and through your chest / heart).
Daniel
Last edited:
Another good basic practice is to install bleeder resistors across the power supply caps, so when you power the amp down, their charge bleeds down over the course of a minute or so. Otherwise, your PS caps can hold a HV charge for quite a while.
I also use clip leads when testing a live amp, and power down while monitoring B+ voltage before moving any leads. With clip leads I don't need any hands in a live amp. Testing/troubleshooting is a little slower, but perfectly acceptable to me.
Also always use grounded plugs, and make sure the chassis is bonded well to the ground wire. It's the most important connection in the amp.
Staying below 450V-500V power supply voltage is also a good idea safety-wise.
I also use clip leads when testing a live amp, and power down while monitoring B+ voltage before moving any leads. With clip leads I don't need any hands in a live amp. Testing/troubleshooting is a little slower, but perfectly acceptable to me.
Also always use grounded plugs, and make sure the chassis is bonded well to the ground wire. It's the most important connection in the amp.
Staying below 450V-500V power supply voltage is also a good idea safety-wise.
One hand rule.. Carpet, nonmetallic chair, shoes, long shirt, all help that work the best. It's all a matter of keeping an open circuit through you. You can take yourself right up to few hundred volts, thousands if you're a little loonie, so long as you don't start any arcs or make any contacts. Although getting rapped through a section of the arm doesn't feel that great, the most damage you suffer might be caused by how you jerk away. I've run myself across some sheet metal edges that way. Somehow the probe tips figure out how to get in the way of where my hands want to go pretty often, which is usually not too fast unless I think I'm getting shocked or I need to "change a connection" in a hurry.
Any project that connects to the mains is inherently dangerous. That said, there are steps that you can take to minimize the risk of electrocution. Monitoring B+ and other high voltages used is one. I use two voltmeters for that reason. One is permanently hooked to B+, the other measures whatever I want. I don't mess with the circuit until B+ has discharged to below 5~10 V.
Don't work on the circuit if you're drunk, sick, tired, or in a hurry as you are much more likely to make mistakes that could turn out lethal.
Make sure all exposed metal parts of the chassis are grounded to the green wire safety ground of your house.
Circuits that operate up to 250~300 V don't generally require any special components. Most hook-up wire is rated at 300 V. For higher voltages, keep in mind that most 1/4W resistors are rated at 250 V so if they have a higher voltage drop across them, you'll need multiple in series. 600 V hook-up wire is pretty easy to find. Once you get above 500~600 V sourcing parts becomes a challenge. Not impossible if you know where to look, but you won't find much at Digikey, RatShack, and the like places.
Stay safe. Work slowly.
~Tom
Don't work on the circuit if you're drunk, sick, tired, or in a hurry as you are much more likely to make mistakes that could turn out lethal.
Make sure all exposed metal parts of the chassis are grounded to the green wire safety ground of your house.
Circuits that operate up to 250~300 V don't generally require any special components. Most hook-up wire is rated at 300 V. For higher voltages, keep in mind that most 1/4W resistors are rated at 250 V so if they have a higher voltage drop across them, you'll need multiple in series. 600 V hook-up wire is pretty easy to find. Once you get above 500~600 V sourcing parts becomes a challenge. Not impossible if you know where to look, but you won't find much at Digikey, RatShack, and the like places.
Stay safe. Work slowly.
~Tom
I remember my first valve pre amp in 1980.
I built it up and tested it and switched it off.
I touched the circuit and got zapped.
Someone told me I had to discharge the power supply capacitor first.
So next time I was clever I discharged the power supply capacitor before touching the circuit.
However I got zapped again ! I had forgotten to switch it off !
I was a nervous wreck by the time it was finished lol
I built it up and tested it and switched it off.
I touched the circuit and got zapped.
Someone told me I had to discharge the power supply capacitor first.
So next time I was clever I discharged the power supply capacitor before touching the circuit.
However I got zapped again ! I had forgotten to switch it off !
I was a nervous wreck by the time it was finished lol
It's no more dangerous to build a single-ended amp than it is to build a PP design. If you use types like: 2A3, 300B, 6CK4, pseudotriode pents, these will typically operate at voltages of around 350Vdc. So do a good many audio finals that appear in PP designs: 6L6, 807, 6AQ5, 6V6, 6AQ5.
If you go for Bigwatts, then you'll be dealing with types like the 845, and will be dealing with voltages up around the 1000Vdc area. You can also do PP designs based on some of the big RF finals that will also be operating at similar voltages.
It's all in what you choose to do. Just because some solid state designs operate at lower voltages doesn't completely eliminate all risk.
There is always the chance to get zapped. You need to pay attention at all times, and not do anything stupid.
I suggest taking a good look at this article: Electrical Safety.
I found with solid state the shocks/tingles start to set in around 100 volts.
I got my hand across +/-60 and got quite a tingle.
1000 volts on a valve amp wont tingle it will kill you !
Every one of us was a beginner at one point, I was about 7 when I started down this road, and now build big and potentially dangerous projects as a matter of course. My current design has supplies at 1.4kV @ 150mA - instantly lethal, and don't think I take that lightly. You tackle what you are ready for at a given point on the experience/knowledge curve. You can SAFELY tackle a small SET amplifier as a beginner. The resources are here - ready for you to read: http://www.diyaudio.com/forums/tubes-valves/30172-safety-practices-general-ultra-high-voltage.html
I'd start with a small simple SE amplifier based on something like the 45 or 2A3 DHTs, or 6BQ5/6V6 (triode connected) - plate voltages in an amplifier using one of these tubes will not be much over 300V even using cathode bias, and 250V if you choose to use fixed bias. (Requires an additional negative supply typically no more than -60V if adjustable bias is used, and eliminates an expensive cathode bypass capacitor.)
Driver tube could be 6SN7, 5842, 5687 or anything else with reason that you fancy..
Everything can be enclosed in a metal chassis with bottom cover, and top cage which is all grounded to safety ground. The metal chassis will contain any mischief in the event of a component failure and keep all hazardous high voltages out of potential harms way.. All that is really required is a little care in construction, selection of the right parts, and mindfulness when working around these sorts of voltages - which are usually not fatal with inadvertent contact, but CAN be.
Any design with supplies in excess of 400V or so are best avoided as a newbie, but a simple SET is doable and I encourage you to join the rest of us.
Next think about efficient speakers to use with your project amplifier..
I'd start with a small simple SE amplifier based on something like the 45 or 2A3 DHTs, or 6BQ5/6V6 (triode connected) - plate voltages in an amplifier using one of these tubes will not be much over 300V even using cathode bias, and 250V if you choose to use fixed bias. (Requires an additional negative supply typically no more than -60V if adjustable bias is used, and eliminates an expensive cathode bypass capacitor.)
Driver tube could be 6SN7, 5842, 5687 or anything else with reason that you fancy..
Everything can be enclosed in a metal chassis with bottom cover, and top cage which is all grounded to safety ground. The metal chassis will contain any mischief in the event of a component failure and keep all hazardous high voltages out of potential harms way.. All that is really required is a little care in construction, selection of the right parts, and mindfulness when working around these sorts of voltages - which are usually not fatal with inadvertent contact, but CAN be.
Any design with supplies in excess of 400V or so are best avoided as a newbie, but a simple SET is doable and I encourage you to join the rest of us.
Next think about efficient speakers to use with your project amplifier..
It's a fact that anything above 45 V. has considerable danger potential. The danger rises exponentially as the voltage rises. "Sand" amps can bite too and the current available in high powered units can produce very nasty burns. Electricity is a wonderful servant, but it must be treated with RESPECT.
Along the lines Kevin has suggested, a 5965 as the voltage amplifier driving triode wired 6V6 family O/P tubes is an affordable and good sounding way to get your feet wet. A highly satisfactory B+ supply can be constructed, at modest cost, by Greinacher ("full wave") voltage doubling the O/P of a Triad N-68X isolation transformer. The eminently affordable Edcor GXSE15-8-5K will yield quite decent, if unspectacular, performance. You will not need a preamp, if a CDP is the signal source.
Along the lines Kevin has suggested, a 5965 as the voltage amplifier driving triode wired 6V6 family O/P tubes is an affordable and good sounding way to get your feet wet. A highly satisfactory B+ supply can be constructed, at modest cost, by Greinacher ("full wave") voltage doubling the O/P of a Triad N-68X isolation transformer. The eminently affordable Edcor GXSE15-8-5K will yield quite decent, if unspectacular, performance. You will not need a preamp, if a CDP is the signal source.
It's a fact that anything above 45 V. has considerable danger potential. The danger rises exponentially as the voltage rises. "Sand" amps can bite too and the current available in high powered units can produce very nasty burns. Electricity is a wonderful servant, but it must be treated with RESPECT.
Along the lines Kevin has suggested, a 5965 as the voltage amplifier driving triode wired 6V6 family O/P tubes is an affordable and good sounding way to get your feet wet. A highly satisfactory B+ supply can be constructed, at modest cost, by Greinacher ("full wave") voltage doubling the O/P of a Triad N-68X isolation transformer. The eminently affordable Edcor GXSE15-8-5K will yield quite decent, if unspectacular, performance. You will not need a preamp, if a CDP is the signal source.
Sounds like all good suggestions here, inexpensive parts, and a large opportunity to learn something new. Later on build the fancy amplifier..
Again do think about what you are going to be connecting this to, in a small room low power might be just fine depending on musical taste. Having a speaker system with > 90dBSpl efficiency with lower powered amplifiers is a given for acceptable results. And the higher the better. (My FRs are 91dB efficient and the Onkens in my main system are >100dB)
How dangerous is it to ride a motorcycle, drive to work every day, or even get out of bed in the morning? Everything in life carries some risk. In many cases (like building a SET amp) the risk can be mitigated with knowledge, and you are in control of the circumstances. In other cases (like riding the motorcycle in traffic) some of the risk is not at your control.
As suggested by others there are places to learn how to deal with and learn to respect the potentially lethal voltage levels used in almost all vacuum tube equipment. I put together a web page explaining electrical safety for those exploring vacuum tube electronics for the first time. Much of the material is from my own experiences:
Electrical Safety
There is no reason why a SET would be any more dangerous than any other piece of vacuum tube equipment. Of course the voltage level goes up as the power rating goes up and it is possible to build a SET that runs on 1500 volts, but I would start with something simple and reasonably powered.
As a lefty, I'll take working with my left hand over my right all day long. If I tried to work with my right hand only I'd electrocute myself on the first day.
To prove this I suggest Loren hold his penis with his left hand while urinating for an entire week. $1 says he urinates on himself at least 3 times. I bet he can't remember the last time he urinated on himself using his right hand.
To prove this I suggest Loren hold his penis with his left hand while urinating for an entire week. $1 says he urinates on himself at least 3 times. I bet he can't remember the last time he urinated on himself using his right hand.
Yes, was about to suggest taking a look at some good advice from George (Tubelab), he has a really good wrap up of the necessities, and having had a few non-fatal frights along the way, strongly recommended reading, and if you are in a 220-240V mains part of the world, more so. Beware of centre tap plate windings, 800-900 volts RMS across full winding is not something to take chances with.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.