burning in an amp?

noworrybeefcurry · Post by **noworrybeefcurry** » Sun Dec 18, 2011 8:45 am

when you first "burn in an amp" before power up, should it be done with or without tubes installed?

teemuk · Post by **teemuk** » Sun Dec 18, 2011 9:34 am

You can make an initial test that supply and bias voltages etc. are correct without installing the tubes. If things look right put the tubes in.

If you really want to "burn it in" then you need to insert the tubes and run the amp for few hours to a dummy load at a level at which the amp has its greatest thermal losses and therefore greatest stress condition it will ever be subjected to in normal use. It's likely not "on ten". On class AB amps the point is likely something close to 60% of full power with the input signal being a square wave but it naturally depends on the design.

If the amp survives that and doesn't develop some "infancy problems" (e.g. solder joints failing, weak or faulty parts failing, unexpected bias drifts, thermal runaways, excessive heating of poorly derated components, etc.) then you have successfully burned the amp in.

rdjones · Post by **rdjones** » Sun Dec 18, 2011 11:07 am

noworrybeefcurry wrote:when you first "burn in an amp" before power up, should it be done with or without tubes installed?

Voltages are going to be higher along the dropping string without the circuits being loaded by tubes.
In particular, the end of the string (near the first preamp) will be at or very near full B+.
This combined with possibly high AC line voltage creates the chance that some filter cap working voltage limits may be exceeded.
You can bring an amp up slowly on a Variac to 'form' filter caps but there's some debate as to whether this is needed with new caps.
It is recommended for old caps that have been dormant for years but such caps should get replaced anyway.
Without tubes there's not really anything to "burn in".

rd

tubelectron · Post by **tubelectron** » Sun Dec 18, 2011 7:32 pm

Voltages are going to be higher along the dropping string without the circuits being loaded by tubes.
In particular, the end of the string (near the first preamp) will be at or very near full B+.
This combined with possibly high AC line voltage creates the chance that some filter cap working voltage limits may be exceeded.
You can bring an amp up slowly on a Variac to 'form' filter caps but there's some debate as to whether this is needed with new caps.
It is recommended for old caps that have been dormant for years but such caps should get replaced anyway.
Without tubes there's not really anything to "burn in".

I can't agree more, and I would also recommend the use of the Variac with new capacitors, even if it is less critical than with used or long-time stored NOS capacitors.

A+!

cbass · Post by **cbass** » Sun Dec 18, 2011 8:07 pm

I don't have a variac so I use my lightbulb limiter with bulbs going from 15 to 100 watts.To form caps I'm not sure if this really does anything or not.May just be a dumb thing to do I don't know

amplifiednation · Post by **amplifiednation** » Sun Dec 18, 2011 10:05 pm

After intial power test using the limiter and checking for shorts, and checking that voltages are normal, THEN you can burn the amp in.

As suggested above it is really to find any potential problems, but also to put some time on the components. Many say amps warm up after 40 or 50 hrs of play...so some burn in time can help you get there.

Using signal and running into a dummy load is a great way to do it if you are set up that way. I'm not... the last amp I built i did a 40 hr burn in, 4hrs on 4hrs off at a time. I used an old 4ohm car speaker and just let the amp "hiss" through it. I used some crappy tubes and just let it run on my bench with a small fan passing air by the tubes. I will do that on future amps I think it had a good effect. I got that tip from one of the pros!

Diablo1 · Post by **Diablo1** » Sun Dec 18, 2011 10:56 pm

After you first test the amp with the light bulb limiter with tubes installed, remove the limiter and set the bias. Start using the amp....that's your burn-in. If and when problems arise, fix 'em.

noworrybeefcurry · Post by **noworrybeefcurry** » Mon Dec 19, 2011 9:57 pm

So the use of a variac to slowly bring the amp up to operating voltage really isn't necessary. I should just use a crappy set of tubes, a signal generator, and a load?

dcribbs1412 · Post by **dcribbs1412** » Mon Dec 19, 2011 10:16 pm

amplifiednation wrote:After intial power test using the limiter and checking for shorts, and checking that voltages are normal, THEN you can burn the amp in.

As suggested above it is really to find any potential problems, but also to put some time on the components. Many say amps warm up after 40 or 50 hrs of play...so some burn in time can help you get there.

Using signal and running into a dummy load is a great way to do it if you are set up that way. I'm not... the last amp I built i did a 40 hr burn in, 4hrs on 4hrs off at a time. I used an old 4ohm car speaker and just let the amp "hiss" through it. I used some crappy tubes and just let it run on my bench with a small fan passing air by the tubes. I will do that on future amps I think it had a good effect. I got that tip from one of the pros!

cool idea
Thanks

M Fowler · Post by **M Fowler** » Mon Dec 19, 2011 10:26 pm

Some builders build the power supply first and test as they go but in builds such as a Dumble the power transformer is placed in last.

Use the variac and slowly bring it up to operating voltage.

Mark

dorrisant · Post by **dorrisant** » Mon Dec 19, 2011 10:36 pm

Can the Variac and bulb limiter be used interchangeably? Theoretically you are doing similar things. I would think that the bulb would give added overload protection though.

M Fowler · Post by **M Fowler** » Tue Dec 20, 2011 2:53 am

Use the bulb limiter if that is what you have.

ampgeek · Post by **ampgeek** » Wed Dec 21, 2011 5:16 am

A quick note of clarification to our less experienced bretheren regarding the use of a variac (or any other voltage limiting device, like a light bulb, for that matter) when tubes are installed: Be aware that your filiment heater supply voltage may also become hobbled.

Cheers,
Dave O.

tubeswell · Post by **tubeswell** » Wed Dec 21, 2011 4:24 pm

"Burning in' an amp is something of a misnomer. The main thing you possibly may want to 'wear-in' is a new speaker (until the rim of the cone and the spider are soft enough for it to sound good). The rest of it is all electronic/electric and will be subject to entrophy, i.e.: it won't get better with use, it will start out good (if it was built properly) and then will gradually (or sometimes even suddenly) deteriorate with use and continual heat. Eventually you will have to build another one

Milkmansound · Post by **Milkmansound** » Wed Dec 21, 2011 4:56 pm

its a good idea to stress the components a little before you sign off on them - especially new production tubes. I've had many of them pop on me within 12 hours of use. I usually run the amp and listen to music through it for a few hours while I am working on something else. Then I play through the amp as much as I can at various volumes. Then I apologize to my neighbors

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