Hi all -
My question might seem basic, but I am new to audio tubes.
What are signs that the tubes on the BHK Preamplifier are starting to show their age? Basically, what audible characteristics can I expect to start hearing as they start to show signs of replacement. I don’t mean when they are at the point of obvious need, but more the beginning stages of degradation.
thanks in advance…
There will be an eventual dullness to the sound. One day you will realize the magic just isn’t there anymore. That is the time to replace the tubes.
Buy an extra set of tubes, then periodically swap the new tubes in for the existing tubes. At some point you will hear that the system sounds better with the new tubes swapped in.
Good advice!
Approximately how many hours on the BHK preamplifier and the BHK 300s?
2,500 hours on the preamplifier
Tube life depends on the types and brands of tubes too. For 12au7 tubes, GL and PSAVNE tubes typically last 2000 hours, after that the SQ would start fading in my experience.
Two brands stand out:
Aptos Ray Select advertised their 12au7 tubes last 10,000 hours. Well, mine have had 2000 hours, and they sounded better than new tubes.
Telefunken 12au7 NOS tubes, everyone says these last at least 10k hours. Mine was a part of tube rolling so there is no where near that yet.
In my experience when the tubes wear, which has happened after around two years of use,
I hear a small amount of distortion, low level but significant. When I replace the tubes that distortion disappears.
I am recently noticing the following: when I first got my BHK preamp and BHK 300’s I would routinely listen to music and a reasonable level from my source at 24-27 in the volume knob.
Now I’m noticing that for the same volume level, i’m up around 34-37 on the volume knob.
Is this a function of the preamp tubes wearing down?
It might be, but it is common for small signal tubes to last many thousands of hours. It all depends on the brand and specific tube. As others have said, the only way to be sure is to get a second set of tubes and swap them out.
When I got my BHK preamp, I did not realize at first that it has a counter for tube hours built in — very useful.
Also, don’t forget that your amps have tubes; they could be in need of replacement.
If the tubes were wearing down, you would notice the magic simply gone from your system. Everything would sound dull and flat and lifeless.
Not according to DChang05. HIs experience is 2,000 hours and they’re toast.
I wrote:
Please note that dchang himself identified two tubes that are known to last much longer than 2000 hours. In my BHK preamp, I have a set of Matsushita NOS tubes with about 9000 hours on them and have not yet noticed any degradation. I stand by my own experience in this regard.
Hate to even suggest this is a possibility, but the range increase in volume control you’re needing for a perceived no change in volume to your ears might suggest you’re ready for a hearing exam. Certainly hoping it’s something else entirely!
You could also use a db meter now and test again in a few months to see if the db to your perceived volume is still changing or not…
Btw, I also have the BHK 300s and BHK Preamp. I had not noticed degredation of sound in 2200 hours, but decided to replace anyhow. I changed tube brand in the preamp but not the amps. Overall I think a slight upgrade in sound, but volume level wise, no impact.
I felt honored that my name is mentioned as if I’m a tube expert 
I’m simply a user and my experience with both BHK pre and M1200 are limited to 12au7 tubes only. Here’s strictly my personal experience:
When I replaced GL tubes in BHK pre (a bit less than 2k hrs.) with the same, I heard quite an SQ improvement. But the Telefunken NOS in M1200 sounded better than the new so I left them there. The original PSVANE tube in one channel died just passed 1k hr. In pre before the GL tubes.
Around 3k hrs. I replaced Telefunken with Apos Ray select (not because there was degradation in SQ, but wanted to try something new). Apos has been in pre over one year so the pair has had 3k hrs at least.
These are from memory, and I didn’t dig deep back to find my old post. I’m still on vacation so my memory could be off a bit🤔