SP14 question

Hi, I am new to this forum, tube gear and to hi-fi stereo in general. I've recently completed SP14 preamp (I got assembled PCB, so only minimal soldering required).
When I power the preamp and start listening, sometimes I can hear a little hum or pops in speaker - this effect seems to completely go away after probably 5 minutes or so. Is this normal or I have done something wrong?

Thank you,
Kirill

Have you tried changing tubes?
Are the tubes NOS?

DavidR wrote:Have you tried changing tubes?
Are the tubes NOS?

Tubes are NOS, I didn't try to change tubes, but I did try to use second output.