Will my TSE zap my children? - Page 2 - diyAudio
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Old 2nd January 2012, 01:59 PM   #11
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Most of the valve/tube DIY builds seen on these pages would not comply to national safety standards.
Virtually NONE would comply with the product safety standards in the US and most other countries. In the US the maximum temperature on any user accessible surface must not exceed 60C. This rules out all exposed vacuum tubes.

Better is to take reasonable steps and then put the amp out of reach of persons who may come to harm.
I have stated this multiple times as well. Curious kids will do unexpected things. My own electronics career started at about age 5 when the paper clip met the wall outlet. Electricity is a useful servant, but MUST be respected. It has the power to kill you.

Earth testing with a multimeter alone is futile. You need to pass some amps between the chassis and mains earth
True, the path from the chassis and all user accessible conductive surfaces must have a LOW RESISTANCE path to the earth ground. Technically to be compliant there must be a green wire with a yellow stripe from the ground pin on the IEC connector to the chassis! Green with no stripe is acceptable in some countries. Black or any other color will not pass UL or CE standards.

A multimeter test does not verify the resistance in the sub ohm range, but a multimeter test AND a visual inspection should be sufficient provided the builder understands the reason for all of this.

The most probable mechanism for an electrical shock related failure in a tube amp, especially a vintage tube amp or a new one built with vintage components is the transformers. If you think about it the transformer is wound with enameled wire and paper or mylar insulation. The only thing seperating the chassis of the amp from hundreds of volts is paper and enamel. A 50 year old transformer may have absorbed enough moisture to start breaking down the insulation. This is why I stress that ALL metal surfaces MUST be connected to earth ground INCLUDING the transformer cases AND the speaker secondaries. I have personally seen two bad transformers in my 40+ years of tube amp work. Both functioned normally but represented serious shock hazards. Both were in vintage amplfiers. One had almost 300 volts on the speaker leads and the other had 70 volts AC on the chassis. BOTH amps blew the mains fuse once the chassis was properly grounded with a 3 wire line cord.

As I stated on my web site the TSE was not intended for novice builders. In fact it started out as a design for my own use that people kept wanting. The grounding requirements are spelled out much more clearly in the SSE manual. The SSE manual section on grounding AND the section on safety should be read and understood before operating the amplifier. If is is not perfectly clear, the amp should be checked out by someone who understands the requirements.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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