Originally Posted by gibosi
As I mentioned earlier, popping, creaking and pinging sounds are quite common with 6AS7G. These tubes have 2.5 amp heaters and they get very hot. And as the tube heats up, these are the sounds the interior metal parts make as they expand. And in my experience the 5998 is the noisiest of all.
Now, I have no knowledge regarding the physical condition of your amp, dust and dirt, and so on, but again, even in a squeaky-clean amp, these tubes are going to creak, groan and pop as they heat-up... and as they cool down. It reminds me of the sounds an automobile engine makes after it is turned off.
Again, my advice, wait several minutes for these tubes to heat up and stabilize. And then connect your headphones, relax and enjoy.
Hi Gibosi, I never heard all that strange noises from my 6AS7Gs, maybe some pops as the tubes heat up. They reach operating temperature after, say, five minutes, but I feel that top sound is only achieved after a minimum of half an hour playing music. I know this does not make sense from a technical point of view, the tube reaches its operating temperature and then stays more or less in that temperature, but what about the preamp, the other circuits involved, and the input tubes ? We are talking about an OTL preamp, in which the 6AS7Gs are output tubes that provide current to drive headphones, and in my setup as a pure preamp, to drive two mono, SS power amps. In this role, it is an extremely powerful preamp, however compatible with the power amp inputs, it clearly dominates the scene and the sound of the tubes are absolutely predominant. I quickly set the amps (NAD 2400 in mono, 450 watts) at 25% power, and this little audio wisdom saved the life of my beloved speakers, some day when I powered up the preamp unaware that the amps were left on from the night before, producing a freaking loud POP that would have kill the speakers for shure, if the amps were set for 100% power. In fact, this same NAD amps have blown two tweeters, one mid and one 8 inch woofer before, with my previous speakers, because its "power envelope" circuit allows dynamic power pulses 3 or 4 times above its rated power. Problem is, rise time is so fast that it can bypass protection fuses and blow the drivers...dangerous amps for sure, but -as you can imagine- extremely dynamic and seriously powerful. And neutral, with the 6AS7G preamp, the NADs sound like tubes, and since the OTL is utterly dynamic and detailed, is like a perfect match. I feel that the sound of this kind of preamp is not at all stable thru its operation cycle, it reaches good sound after half an hour, but it have ups and downs, after two hours, maybe it reach its best, but this is my subjective opinion, of course...