The danger of building a tube amp..?

[therealfindo]

OK, potential dumb question.. But... The danger commonly associated with building a tube amp is only really there if you don't get it right before powering up the first time, right?

 

[clintj]

No. Even if you get lucky and get an amp that works properly the first time (rare), you'll still need to get actual plate voltages to properly set bias on a fixed bias amp. You may also end up with lead dress issues, hum, miswired OT leads, you name it. I also check all voltages for power supply, tube pins, etc to confirm everything is working as it should. Odds are, you'll also be in there later for tweaking, eventual repairs, maintenance, and so on. All of these require entering the chassis safely, and sometimes working on live circuits.

 

[CVTele Dan]

The real danger in building a tube amp is the associated gas to build more....

 

[Jupiter]

The real danger in building a tube amp is the associated gas to build more....

This is the main thing that scares me away.

 

[src9000]

This is the main thing that scares me away.

Me too.

 

[Dingbat]

But but....when you do build, say a 5E3, and it sounds just right it's like being in love

 

[clintj]

The real danger in building a tube amp is the associated gas to build more....

LOL. Boy, is that ever the truth. And a BFSR, and a Bassman, and a Marshall, and a Trainwreck....

I need a 12 fret program to kick this habit!

 

[teleamp]

Deburr that chassis first...

 

[rwsand]

No. Even if you get lucky and get an amp that works properly the first time (rare), you'll still need to get actual plate voltages to properly set bias on a fixed bias amp. You may also end up with lead dress issues, hum, miswired OT leads, you name it. I also check all voltages for power supply, tube pins, etc to confirm everything is working as it should. Odds are, you'll also be in there later for tweaking, eventual repairs, maintenance, and so on. All of these require entering the chassis safely, and sometimes working on live circuits.

Take some time and read up on servicing amps. That will give you a good feel for these things.

 

[Bill Moore]

It is an addiction!
I was telling my brother in law about my latest project, and he laughs, and says 'how many amps do you have, anyway?" I tell him 10, and ask him how many Harleys does he have now. He didn't say anything, just got up, and got us another beer.

 

[tony hunt]

A while back I did the maths of building my own amps, but only after about ten or so builds.
I don't build anymore. Repairing vintage amps worked out more cost effective.
Be honest about your time and you may find that you are already in the pre CBS Fender league. But, building ten amps tells you a hell of a lot about repairing old vintage ones. A jouney can always be fraught with danger.

 

[wmsimpson]

...Be honest about your time and you may find that you are already in the pre CBS Fender league.

I have plenty of time... Money, not so much.

 

[keithb7]

I built 3 amps. I learned a lot. I kept very close attention to my costs. Cheaper to buy vintage in several cases. Champ, vibro champ, Bandmaster cant build them for their market prices. Resale sucks on home built. Better iff buying a clone someone else built. However the experience was fun and rewarding. Now I too repair vintage amps. Keeps me into a great hobby and I get paid to do it. Lots of fun!

 

[Ricky D.]

OK, potential dumb question.. But... The danger commonly associated with building a tube amp is only really there if you don't get it right before powering up the first time, right?

No matter who you are or how experienced, there's no guarantee that the amp you build will work properly the first time you flip the switch. Far better to learn a few simple rules and procedures that will keep you safe.

Here is a link for you.

http://www.aikenamps.com/index.php/safety-tips-for-working-on-tube-amplifiers

 

[Jsnwhite619]

Yeah, as stated above, the real danger lies in the fact that as soon as you lay down the soldering iron, you're going to be pricing out how much the next one is going to cost. It's a gateway drug.

 

[czech-one-2]

Resale sucks on home built.

Hate to be a downer but it's not really worth it in the long run.
Fun hobby though!
Dangerous? Well, even putting in a plug at home could kill you if you don't follow some simple safety precautions.
The one that stuck with me is never put two hands in a live amp. [Don't ask me why this stuck]

 

[Gnobuddy]

The danger commonly associated with building a tube amp is only really there if you don't get it right before powering up the first time, right?

With that much voltage inside, there are always going to be risks.

I don't think it's a great idea to build the entire amp at one go and then power up the whole thing. I build and test one functional block at a time.

I first build the power supply, then test it; first continuity and resistance tests before power is applied, then apply low voltage AC with a Variac, or use a series light bulb for protection if you must power up with full line voltage. Wear safety goggles and Class 00 (500 V) or Class 0 (1000 V) electrical safety gloves. Final tests are with a voltmeter, with the power supply powered from a 120V safety isolation transformer.

The use of an external safety isolation transformer is rarely mentioned on this forum, but I learned from a forum frequented by well trained and experienced tube techs and electrical and electronic engineers that it is a vital piece of safety equipment. Among other things, it can prevent the destruction of your test equipment in case something is wrong with the amp you're testing.

Once the power supply has been built and tested (and all caps fully discharged - I always add bleeder resistors across each filter cap), then I build and test the output stage (power tubes, output transformer, fixed bias if any). A dummy 8 ohm load is used instead of a speaker. You must understand the circuit well enough to ensure the tubes are safe - the bias voltages and currents must be correct and present to avoid damage to the tube. You cannot leave out grid stoppers or grid bias resistors, for example.

After the power amp has been tested (that includes setting bias currents and checking all voltages), next up is the phase splitter.

The phase splitter gets the same treatment, and once it's working and passes all voltage checks, I build the input stage to the power amp section (the driver for the phase splitter), if any.

At this point you have a working power amp. You can even play your guitar through it, by using an external stomp-box or two as a make-shift preamp. I like to use a Danelectro Fish-n-Chips EQ pedal, because it provides both EQ (tone controls) and (perfectly clean) gain.

With the power amp built and working, I start on the preamp. With the preamp, you can either start at the final preamp stage and work backwards towards the input, one stage at a time, or you can start at the input, and work towards the output of the preamp, one stage at a time.

Obviously, to avoid internal damage, you have to make sure both triodes inside a 12A*7 tube are properly biased before you apply power; that means you add enough external components to keep the triode safe, even if you're not yet putting that triode into the signal path. In a preamp stage, both control grids must be properly grounded, and if one triode is unused at this point, ground it's cathode and plate as well to keep it happy and safe until you bring it into use.

By building and testing each stage in turn in this way, you have a chance to catch any mistakes you make, one at a time. This is usually relatively manageable.

If, on the other hand, you build the whole thing in one go, particularly if you're inexperienced at this, you may have multiple errors and mistakes to fault-find, and that can be a very difficult job even for an experienced trouble-shooter.

Divide and conquer. It worked for ancient Roman leaders, and it works for contemporary amp building even better!

-Gnobuddy

 

[Silverface]

Separate from testing each stage s one is built, the real danger in building tube amps is people building them without knowledge of simple electronics.

I see far too many players get into trouble - safety or success-wise - by buying a kit to build thinking they can just follow the "instruction manual" lie it's a piece of patio furniture.

Electronics operates through a different sense of rules.

IF you don't understand Ohm's law - forget it. If you don't know resistor color codes without having to look at a chart - forget it. If you don't know the basics of how current and voltage flow through an amp - forget it.

Learn basic electronics...especially electronics safety...first. Build some simple little projects. But don't tackle an amp build if you don't understand how one works.

 

[FenderLover]

Operating a perfectly tuned vehicle on a public street can be dangerous. There are many life threatening situations every day that can go very wrong, but we go into these situations with our eyes open.

The trouble is, we start working on amps and building amps in part to learn how they work, not the other way around. Quite a few people on this forum are examples of that - they didn't get tech degrees before working on anything. At best it might happen in parallel. Most of us learn by doing. While high voltage is dangerous, common sense should negotiate ultimate peril, like every dangerous situation common in daily life. You'll eventually cut your finger; you'll eventually get a shock; suck it up or turn in your Man Card and sell all of your power tools...

 

[6942]

I put in voltage test points on the chassis surface.
That way, I do NOT have to start poking around inside the amp, and possibly.....'zaaaaaaap'.....my sorry butt.