G9 humm...

[Soeren_DK]

I tried to find an old topic I had wrote but it is gone. Great... but anyway...

I have som hum in my G9 preamp. I my seach I suspected the tubes. The tubes a some Sylvania 6189. When I carefully hit the tubes with my finger I can hear a sound in the speakers a little like a microphone. Someone experinced that some tubes could be defect.

(Sorry for my bad english)

 

[Rob Flinn]

When I carefully hit the tubes with my finger I can hear a sound in the speakers a little like a microphone.

That is not uncommon. Its is called microphony. Some valves are more microphonic than others.

 

[Soeren_DK]

[quote author="Rob Flinn"]Its is called microphony. Some valves are more microphonic than others.[/quote]

What does that mean? And it is good to have en this kind of preamp...

 

[gyraf]

That depends on how loud it is.

All tubes are "microphonic" to some degree - but once in a while you come across one that is unuseable because it's too much.

But allow the unit to warm up/ burn in for some hours before judging the michrophonics of the tubes. This will often be reduced when properly heated...

For the hum, read the G9 thread about proper grounding..

Jakob E.

 

[Soeren_DK]

Okay I will do that.

When I turn the Output pormeter and the gain to zero the low frequenced hum still is their....

Some maks from my meter.

HT on the therminals to the caps = 242.2V
Heather = 11,55V
Phantom = 48,6V