Help needed - Excessive noise from fan in LSS

[kulibu]

Dear Lone Star Special experts,

I have problem with my LSS that just occured today. There is a slight "howling" sound that is independent from the input (still there when guitar is fully muted) but increases when increasing the master or the ouput settings. It is on both channels and seems to decrease a little whith the amp warming up. Takin out the fx loop has no influence (other than the increase associated with the overall increase in volume.)

Now when I switch off the fan, the noise decreases a lot. To make it clear, I am not talking about the usual noise of the fan running, this normal fan noise is independent from any volume setting (and also at a very acceptable level when playing). Could I have a tube that has gone microphonic? Any other suggestions?

Thanks in advance for any help,
kulibu

 

[Boogiebabies]

Sounds like you may have a bad preamp or possibly a power tube. The fan is run off the 12V heater supply. A tube may be picking up stray frequncies from the filament supply and it diminishes when the fan reduces the load on the supply, probably parasitic. Try the preamps first, then the power. The LS has a ferrite bead before the input so it does not pick up radio stations and a 12V regulator to make sure the heaters are always constant.

Is there noise with not instument plugged in and the master volume up?