To all "would be" tube amp builders...

[Peter Snowberg]

Hi all,

I keep hearing the same concern over and over about getting into tube amps which is concern about getting electrocuted.

This is VERY well grounded fear (pardon the pun).

Now on the other hand... if you don't have the thing plugged in while you work on it, and you have a bleeder resistor in your power supply, there is really almost nothing to be concerned about.

I was almost killed by a stupid move that I made while working on a Fender Super Reverb. It was 100% my fault because I wasn’t giving the amp and safety procedures my full and undivided attention. Please don’t repeat my mistake.

If you go to the hardware store and get a voltage tester that looks like a little screwdriver with a neon light inside, and use that along with your DMM, you can figure out really quickly where any serious danger lies.

When I work on a tube amp, I make sure I have the unplugged plug IN PLAIN SIGHT in front of me. Next, I check for voltage with a DMM to make sure it's safe. Often, I'll then clip a jumper from the final power supply stage to ground just to make sure there is no charge left.

If you're afraid of having a meltdown, start with a cathode biased amp design, and use fuses. Fuses are a good idea in any case. I try to never build without them. Another thing that helps.... just like starting to build effects... is to start small. Doug Hammond's FireFly is an IDEAL design to begin with and you'll probably love the results too.

Finally, this is the place for effects, and http://www.ax84.com is probably about the best place for DIY amps. Between these two sites, all you need is a soldering iron and a guitar.

Take care and best of luck with your builds!
-Peter

[JT]

To Be quite honest  i consider myself an intermediate beginner in electronics . I have more trouble building FX pedals than amps. Been doing electronics type projects for a few years and had no experience when i started.I have built 2 18 watters, Tweed deluxe, JTM45 and a Tube reverb basically without a hitch. On the other hand almost every pedal i build has a Hitch Respect High Currents ,  Don't be careless and learn when to walk away and you'll be fine building amps .JMHO

[Nasse]

Peter Snowberg wrote:

concern about getting electrocuted

Wise words, and many great tips summarised in few sentences, and same kind of thoughts has been in my mind. But dont ask me how I learned it... :oops: ...For my luck there must have been something that limited the current, though the voltage was high...and yes, there excist instrument strings that conduct current...

That bleeder resistor and little patience till the voltage slowly drops idea is so good that it should be mentioned in all diy tube projects. If you can do it with just one resistor at mains supply that is simple. I must have been very tired because once I read about some tube project I thought I need a separate bleeder resistor for all big electros... but it must have been a "fuzzy" circuit in my mind ...but if you fiddle with components that close the circuit to the bleeder...  :x Do that voltage check!

There was talk at another forum, about same topic. One great safety tip mentioned there was that you should avoid working with high voltages when you are tired. Take a break. And beer and tube amps enclosure open don´t mix. I once worked as a foreman at the building site and had some workers, and I can tell ya that even a hangover multiplies the risk of injury. And it can do so few days after...

PS. A tube amp can be used like as effect box, maybe big one

[smoguzbenjamin]

Peter, how big would you suppose that bleeder resistor has to be, 1M? bigger, smaller perhaps?

[Eric H]

Peter, how big would you suppose that bleeder resistor has to be, 1M? bigger, smaller perhaps?

1M is too large, and will discharge the caps too slowly. If you make it too small it puts too much load on the power supply. 220k is the most common compromise I've seen, and has been used successfully for a VERY long time
:-)

-Eric

[Joep]

220k is indeed a good value. You should use a high wattage resistor (5W or more) for this.

[Paul Marossy]

I am always very careful whenever I am "poking around" inside a tube amp. I don't want to check out early!

Speaking of poking about, here's a little tip that may help someone out there. If you're having problems with noise or hum, and want to see if moving this wire or that wire has an effect on the noise, you can use a pair of wooden chopsticks (or plastic) to push wires around and stuff. I have a pair of liberated chopsticks that I have had for a long time. I put a little bit of red paint on the ends for easy location of the ends.

I did get little zap recently from my Firefly build, after it was powered down for a little while. I was touching the chassis and my finger was somehow touching the negative end of one of the filter caps, and I could feel a little bit of current moving thru my left hand. It wasn't real noticeable, but it wasn't beyond my perception. It was kinda weird...

[petemoore]

I would say something about just being calm, rested, and certainly not rushed or perterbed about anything.
 I'ts very easy to become perterbed when buggin around with electronics.
 That walk away sentence is quite valid...disclpline...be certain you're calm, relaxed and focused.
 I used to find myself getting easily stuck in 'fix' mode 'till a fix was found...9v is ok for that [except for fried nerves] 350v...another 'realm' entirely...basically if it plugs into the wall and has caps...look at what you're doing from the 'right' perspectives...safety first.

[Doug H]

Peter, how big would you suppose that bleeder resistor has to be, 1M? bigger, smaller perhaps?

I'm using a 270K/1W on my current amp build. Most people use 220K.

Doug