Tube Pre+ Transistor Power will burn your power Amp. easily?


I used to combine with a tube pre + transistor power with the ideal sound which I prefer. But one of my friend told me recently that such kind of combination will burn out power amp. easily if I use a tube pre.

Is this theory or practice true?


faust168

Showing 3 responses by erik_squires

@response34

That IS interesting. Since the caps pass AC, it’s possible a very high voltage ( >> 30V) turn on thump could occur. However, honestly that would damage the amp even if off. It would most likely break through most electrolytic coupling caps and if DC coupled, short several transistors. Of course, if a speaker was connected, things could get even worse! :)

Perhaps what tube preamps really should have is a coupling cap + zener diodes to prevent the possibility of high voltages reaching outside.
LIttle more:

Not all tube pre's have this minimal risk. For instance, if the output is transformer coupled, or balanced. Most tube pre's are single ended.

If you truly have a vintage pre-amp (before 1980's) then you absolutely owe it to yourself to check the coupling caps (input and output) and replace all with modern film types.  Electrolytics will be failing by now, and older films just didn't sound as good. :)

Best,


E
Not true, so long as the Tube pre is working correctly.

However, there IS a failure mode which will cause this. Tube pre's have hundreds of volts of DC offset. This usually stays inside the pre-amp thanks to an output coupling cap.  I quoteth myself:

Most tube preamps are 2 very nice output coupling caps surrounded by tubes and a bunch of other stuff

If this coupling cap should fail (extremely unlikely with modern FILM caps) then yeah, you have insta-death of the amp.

Tube amps are going to be more immune to this problem but not entirely.  They usually have their own film input caps, and tolerant of high voltages anyway.

Best,

E