I wanted to share my experience with a rebuild power amp.

I got a CM LABS 912 used at a very good price and the
review here about the CM LABS 412 encourage me to invest
in the rebuild of this power amp. The tech has 40y of
experience in rebuild power amp so i was in trust. Note
that i do'nt ear the amp before to buy he was directly
jumped to the tech shop. When he finally came back
i was very exciting to ear how it sound... It was a big
deception and i think may be i have made a bad move
buying this amp. But i read other review here who member
was speaking about burn in time for a new item or a rebuild
electronic. So i follow the instruction and was ready to
give a minimum of 500 hours.

In the start it like the sound was missing bass, not invol-
ving a dry sound but with a sweet clean signature not bad.
I was ready to sold the power amp and was looking for an
other one... After 150h i start to ear good thing more bass
like the power amp start to open is true nature. But in the
230h wow the sound came to a very good level of quality i
was looking from a power amp. I was close to buy an other amp but cancel the buy before the seller answer me.

The upgrade is not finish but i will put a Furutech fuse and
Cardas binding post with a after market power cord. Now
i'm pretty happy of my buy and will wait until 500 to start more upgrade. What is funny it that CM LABS do"nt command
a higher price like Marantz,Mac but the quality is there and it was made in USA...

The princile of my writing is to encourage other that if
you got a new unit or a rebuild one it possible you regret
your buy BUT GIVE A BURN IN PERIOD of 300-500 hour before
you made you final opinion and you will be happy after...
I had a similar experience with a Bedini amplifier that needed one channel entirely rebuilt. The work was done by an experienced technician who was known for his knowledge about Bedini amps and had fixed the unit before. Well, when I got the unit back I was horrified how bad it sounded. I thought for sure he bungled the job. Only after four months of use did it come around to the sound I knew it once had. Can't say how many hours it took because I didn't time it but the moral of this tale is when you have a amplifier rebuilt, please, give it A LOT of time to burn in!
We have a warranty reactivation policy associated with updates (rebuilds) to our older products. Quite often our customers experience a break-in aspect not unlike buying a new unit. It does also seem to take some time- 300 hours or more sounds about right based on customer feedback.