Re: [Harp-L] Noisy Amp

[MARK BURNESS <markwjburness@xxxxxxxxxxxxxx>]

Most likely a noisy preamp tube, replace V1, V2 & V3 one at a time, with a known 
good tube, powering up/down in between until you have eliminated the culprit. 
For testing purposes it's not necessary to fit a 12A#7 of the same type that you 
took out, but obviously you will need to do so to replace the duff tube if no 
spare of that type is on hand.

Blues Jrs often still make sound with the volume turned to zero, so this might 
not be indicative of anything in particular...e.g. if it makes unwanted noise 
with the volume up, it may well still do it with the volume off.

If that doesn't cure it, try putting the amp in a dark room, where you can see 
the power tubes and powering up whilst looking for any flashes/arcs in the power 
tubes.


________________________________
From: Ken Banks <kwbanks@xxxxxxxxx>
To: "harp-l@xxxxxxxxxx" <harp-l@xxxxxxxxxx>
Sent: Monday, 22 August, 2011 16:25:07
Subject: [Harp-L] Noisy Amp

Hi Everybody,

When I fire up my Blues Jr., it makes a hellacious racket for about 30 seconds 
and then quiets down and works normally. It makes the noise even with the 
volumes turned of zero. Is this caused by a bad tube or tubes? How do I check?

Aloha and thanks,
Ken