I need help to figure out if power up hum on my recently Built 300B SE amp is normal, or what does really cause it?
Every time when I power amp up, it generates very loud hum for 3-5 sec, than the hum goes away and Amp is working fine.
The other mystery I can't solve, same amp does not like to work with signals generated by phono carriages (of cause coming out of phono preamp , and the preamp is not a reason ), as soon as stylus hit the record and moves little bit (even slight vibration), I can hear foreign notice on background very similar to start up noise, but much lower in the level. Interesting enough that all other sources of input signal like CD player , phone etc. do not have this issue.
Any ideas will be really appreciated.