Safety with high volts: 101

[rick57]

I’m going to China where Yarland brand (made in Shanghai) 25 watt 845 SE amps can be had for very low prices, with probably pretty average parts quality.

Later as money permits, to upgrade.

People say be wary of safety with high volts (1100?) amps.
I know virtually *nothing about safety with high voltage amps.
What does that mean?
I’ve googled & searched here a bit and learned little relevant.

All I know is that 240 volts can kill; and 1100 is more likely to arc.

How do you stop arcing?
Get a tube man buddy to inspect the grounding?
Can any tests be done?
Do I need to operate the volume control with thick rubber gloves?
How do I ensure my kids still have a father?

Cheers

[Tekko]

That is pushing it Actually you don´t need to worry at all, all parts carrying the 1100 volts is well insulated inside the chassis, i also think there is a additional steel cage to protect the tubes so no need to worry.

[rick57]

I hope you’re right

Pax vobiscum

[SY]

The arcing is a preliminary to the kill. When voltages get high, you often don't need to touch a rail to die- the electricity will come to you.

Of all the dumb ideas in home audio, high voltage output stages rank in the top 10.

[rick57]

Mmm a touch more cautious than Tekko


OK So if we seek a 845 SE - how do we avoid the dumbness?

[SY]

By not choosing a tube that requires high voltage and a high primary to secondary turns ratio.

[jackinnj]

about once evey other week I get to suggest to fellow DIYr's that they purchase the ARRL Radio Amateur's Handbook or the volume put out by the Radio Society of Great Britain - the ARRL handbook speaks volumes about safety.

Some tips --

1- work with one hand only
2- just because a capacitor looks discharged doesn't mean that it is
3- use a rubber floor mat
4- make doubly sure that the power supply is unplugged before working on it.

with respect to capacitors, it was recommended that every ham radio op (those of us who built and tested their own transmitting equipment) make a shorting stick -- this would be a piece of bakelite rod -- on one end there would be a probe with a piece of ignition cable attached to the chasis ground. after the power was turned off and the amplifier disconnected from the mains you would use the probe to touch the tuning capacitors, chokes, plate connectors etc. to make sure that they were fully discharged. DON'T DO THIS WITH A SCREW DRIVER !!!

btw, it's not just the electrolytic caps which hold a big wallop -- somewhere I have a pair of lineman's diagonal pliers with a big bite out of them from a friend who cut through a live cable -- he survived.

[rick57]

(I’ll read the (just seen) 55 post thread on safety as well).

SY
Are your concerns more about building, modding or simply using a high voltage amp?
If you want 10-15 watts, would you suggest a 300B?? I believe they can sound woolly, but this is > 250 Hz. Is that outside the ‘woolly zone’?

jackinnj
Thanks for your tips.
Do you have concerns about simply using a (pre-made) high volts amp?

Neither of you mentioned checking the grounding checked by someone who knows what they’re doing – is that useful?

Thanks

[Colt45]

just don't open it up and prod around with two steel rods and you should live.

[Enzo]

240volts can kill you and so can 1100 volts, not to mention everything in between. That 1100 volts might be more likely to arc than 240 is not relevant. It is all about what happens when you touch it. 1100 volts won't arc far, and your skin is not a very attractive conductor through the air. If you get within that millimeter or two that an arc can cross, chances are you will be touching it real soon anyway. So I don't worry about it leaping out to get me so much as I do my laying my skin on it.

But that 1100 volts can stop your heart if it runs through you. ALWAYS work in the chassis with power removed, and make sure the caps are discharged. There will be times you have to work with a live circuit - taking voltage readings for example - and then you need to be extra careful.

I always hear folks saying to use only one hand. I think someone said that once and no one questioned it, and we have been repeating it ever since. But if your one hand touches that 1100 volts while your arm is touching the chassis, BOOM you just found yourself on the floor. One hand does not make you not a target. And it is exceedingly difficult to check the voltage across the screen resistors with one hand.

One hand or two, the thing is to be congnizant of what you are touching and aware of the voltages present - or potentially present.