Can power tubes make Hiss?

[alanfc]

hi, I have a question on Hiss,

My master boost never used to make hiss, on my 1993 Rivera R55-112. On channel 1 Brit channel. But now it does....
Now once I use the master boost (must have, sounds great) there's alot of hiss.

I had new SED EL34's installed and biased about 2 months ago.
I wonder if SED's have problems in general? Unfortunately these were not bought from a rigorous tube-tesing vendor.
I've traded around preamp tubes, checked my guitars and cords. No change.

More -
I tried different guitars, removing different pedals from the lineup, turning off all lights and computer monitor, traded changed new old preamp tubes in all positions. Also tried I through different speaker cabs.
It always made some normal sounding hiss, but at practice this weekend I found myself having to turn off the boost between songs, never used to need to do that

thanks

[Wakarusa]

A big source of hiss is "shot noise" (basically the sound of electrons running into something.. like the guts of a resistor... or the plates of a tube). I suppose some power tubes could hiss more than others. Also possible that the fresh tubes, perhaps running at a new bias point, have exposed a stressed resistor.

[alanfc]

fascinating,
OK my tubes =are = new. I hope this is not my problem !

I think I need to test this alot more with all my pedals & everything, to eliminate them first ! And try batteries perhaps.
thanks

[Gary Ladd]

Hissing usually indicates a capacitor(s) is going bad....

[alanfc]

gaaahhh I hope thats not it:( :eek: