• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube preamp overheating characteristics?

I have a tube preamp I didn't build. The cover it came with did not have any vents and I was concerned about overheating so I got another cover that has slots on the side for venting. After a while the cover really was quite warm...not too warm to touch but warmer that I thought it should be.

I could have sworn I heard the music I was listening too becoming distorted. Is this a characteristic of an overheated tube preamp or amp?

I took the cover off and everything sounds fine...even after listening for 4 hours.

I'm thinking I should probably add more slots or holes to the cover on the top.


Paid Member
2011-02-26 2:12 am
Bozeman, MT
Valve amps in general should have good ventilation.
That is why you see commercial power amps having a mesh top cover.

However......in a preamp the tubes will get to a couple hundred degrees which over time can push any capacitors outside their rated temperature range.
This can cause distortion and short life span under the "wrong" circumstances.
Not only that, but if the resistors used are carbon composition (almost perfect cylinders) they can have poor temperature stability and change greatly when overheated.