New amp break-in/ repair stress-test procedure?

[lonote]

I am wondering what type of testing/burn-in/break-in people are doing after completing a new amp, &/or even just a repair, to be confident that the unit is ready to head out the door?

White noise for X hours? Maybe live signal/looper for X hours? Just being powered on overnight,etc..?

[TUBEDUDE]

With a new prototype, after all resistance, voltage and dissipation checks, I do tone, bandwidth and power tests, let it bake for a day, then play the crap out of it daily for a month.
After a repair, the testing depends on the nature of the repair. Blown transformer with cooked tube sockets gets more attention than a cold solder joint.

[Stevem]

First off you need two 8 ohm 100 watt heat sinked load test resistors.
Two ohm so you can wire them in 16 or 4 ohm I'd needed.

You also need a non battery powered audio generator so you drive the amp for 3 hours to at least the point where the power supply V+ on the plates of the output tubes is just starting to drop voltage from what it had been at idle.

It would be real nice to have a scope also.

This is a starting point for the gear needed if you want my 2cents worth.

With most amps and not even high gain ones I find that .150 volts of 800 hz signal into there input will be more then enough to drive a amp to max peak wattage, no less max RMS wattage.
Of course without a scope or a way to test for THD you will never know how much clean RMS wattage you amp under test is outputting.

[xtian]

Geez, I’m a slacker. 80+ builds and no failures after working out build errors, and I don’t do any burn-in. Though to be fair, I’m aware of only a dozen or so that are regularly gigged by musicians other than myself.

[maxkracht]

Poking everything with a chopstick is good practice, in my opinion. Especially with p2p stuff and older equipment that might have some dirt or corrosion. Along with that, looking at an amp from multiple angles is really important. Something can look fine from the back but horrible from the front or side. I've seen a surprising number of vintage amps where a solder joint was completely missed at the factory.

I don't have a standard stress test, definitely goes on a case by case basis, but at a minimum you need to get the amp to a working temperature and try it at full volume. Scope and dummy load will save your ears, but a mostly resistive load can hide some things. Sometimes I will put a blanket over the chassis to make it cook a little extra.

[lonote]

Thanks for the ideas, I will give those a try.

I usually keep the amps I build, but I have one going directly out the door soon, to a friend who plans to gig it occasionally, which raised the question.

With my own stuff, they are around to try out whenever I want & I will often use them at a practice to make sure everything is working as it should.

[beasleybodyshop]

My typical test is to run amp into dummy load, calculate max power (vRMS just before clipping squared, divided by load resistance) and then run a pink noise generator into amp. Reduce output to 1/3rd max power and let run for 6-8 hours. after this, tapping on the chassis with a rubber mallet is a good physical shock test. If it passes all those things then it will likely survive past infant mortality.

[Guy77]

I also run a similar procedure as beasleybodyshop does on the last 60+ new builds I have done.
I like to calculate power by seeing where the sine wave starts clipping as my signal generator runs signal into the amp.
This burn in test is done only after I have ironed out any errors and inspected every solder and checked that all the voltages in the amp is accurate.
If the voltages are not accurate and the amp does not sound right when I play it I do not starts this burn in test.

The best part of running this test for several hrs is that I often catch bad preamp tubes during this test and I have caught several in the 300 or so tubes that have been used in my builds. Its really important to have a strong enough dummy load when running this test. I like to use 300watt resistors for this.

If you google Dr Z amp testing on youtube you will see that he also uses this process to weed out bad tubes.

Cheers
G

[R.G.]

One handy test is to use a Kill-A-Watt or similar AC power meter. It's a quick way to see how many watts the amp is eating from the wall to make how many watts of audio. Very insightful, especially if you have a notebook of previous amps' appetites.