Tube Life Deterioration Characterisics

I have a BHKpre and BHK300’s. I’ve had them long enough that I have replaced the stock tubes in both once, and when I did, replaced them at the same time so that I could use the tube timer in the BHKpre to track installation time. Currently they are at about 1500 hours and I remember when I replaced them, it was a significant improvement, but wondered if anyone had experience to describe what sonic drop off after peak was “like”… Sound stage, brightness, mid-range etc… Paul replaces annually… Anyone do it based on tube time? Cheers!

I replace the tubes (Tungsram 7DJ7’s) on my BHK pre and 250 every 2,000 hours, give or take. The new tubes typically sound louder but I have not attempted to level match so I couldn’t say whether there was really any significant degradation in the sound quality of the old tubes as opposed to just not being quite as strong. The old tubes still sound good so they get put in storage in case there is ever a major tube shortage.

I would have thought you’d get a lot more than 2000 hours out of the 7DJ8’s especially in the BHK preamp that will only be feeding it 6 volts. Are you replacing at this age because you can hear deterioration in the sound or are you replacing them based on advice that they will only last 2000 hours? I have a few sets myself that I bought for my BHK pre’ so I’m interested to know.

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2000 hours translates to a little over a year for me. Arnie Nudell, and maybe Paul too, recommended changing tubes about once a year, in part because tubes are relatively cheap. They could certainly be used much longer. As noted, fresh tubes do seem to consistently sound a little stronger but that might just require turning the volume up an extra click or two. I don’t do it because I hear a qualitative decline but then slow deterioration is harder to hear. If you are happy with the sound I would not stress over it. When my main preamp used 6H30P tubes I would go considerably longer with no noticeable ill effects, but those tubes were reputed to be good for longer periods and also cost more than what I’m using.

If the BHK250 / 300 is on stand-by, the tubes will not wear … Is that correct …?

I picked up the BHK Preamp the first week of JAN, 2019 and changed my BHK250 & BHK Preamp with “special” tubes it came with and added tube dampeners. ON/STB cycling the AMP/PRE every day; make a habit cycling them at the same time; using BHK Preamp tube timer to qualify the BHK250 amplifier tube time. I have 877hrs since week one. Full disclosure: bought a set of Utopia HPs and wanted to make sure the HP circuit and preamp output circuit had 250+ hrs before critical listening. In addition, push the infant mortality of the new BHK Preamp by running it 3 weeks, 24hrs a day. 12hrs speaker, 12hrs HP with Utopias hooked up and running. That was 888hrs with 12hrs the remaining days. If I run my system from 6:00AM to 8:00PM, that is only 5,000 hrs on tubes. So, do I change them to change the characteristics of the AMP/PRE or just because they degrade. I think half the life they will not degrade; however, I think changing them to try out different sounds is fun, not a must. In my situation, once every year and a half since my birthday is in July is a nice compromise… :slight_smile:

I’m in agreement as to understanding peak WOW that sounds great (to me ~500hrs) and when it will sound… crap I should replace the tubes. I assume it will sneak up on me as @stevem2 indicates. So, once a year for 5,000hrs use seems OK; however, going for 7500hrs (1.5yrs) and see if I notice the difference around a year… that is a tricky call… If I got 2,000hrs a year, I would definitely replace them every 2-3 years. Unless you want to hear a different sound and that is what is cool with tubes.

yes, that is why I use the PRE as an indicator of BHK250 tube life… as long as you go ON/STB the same time… and change them the same time…

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Great, thx

All of my components are on 24hrs a day, 365 days a year; except the BHK250 and BHKPRE. I never turn them off, just ON/STBY using the blue PSA logo button, never touching the component ON/OFF switches in the back or shutting down power to the components by turning the P20 circuit OFF. Tubes warm up very quickly compared to solid state electronics. For the ADD; BHK manual: “When the logo standby button is not lit, the amplifier is in the standby mode, and the vacuum tubes are turned off. Standby mode keeps the solid state circuitry of the amplifier in a reduced power mode, maintaining excellent performance benefits while consuming little power.”

Therefore, based on that information I use the BHK Preamp as an indicator of the tube life of both the BHK Preamp and BHK250 Amplifier. As long as the tubes are changed at the same time and the units are cycled (ON/STBY) at the same time daily.

Turning ON the PRE/AMP every morning, the first thing before making my coffee. In the evening I turn off the source music (iPAD Roon), allowing 30min for the REL subs (S3/SHO) to realize the input signal is missing (timer), then turn both AMP/PRE to STBY. It has become a habit. This approach with the REL subs has never resulted in hum in both the ON and STBY modes for the BHK250 amplifier. After adding a nice RCA L/R line from the BHK250 RCA input L/R connector to the L/R LRE input to the REL sub amplifier and turing the LRE amplifier volume potentiometer CCW, then isolating the REL sub black wire.

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That is correct. In the standby mode only the MOSFETs are active. The vacuum tubes are turned off.

Greetings: I have been asking the same question and there seems not to be a definitive answer when to change the tubes on the PS amp and pre. I have been through a couple of sets but am now using some tubes i got from Upscale Audio and i am at 2000 hours on them. They still sound good so perhaps they have not degraded much from the beginning. I have a spare set and will probably try them in a month or two. here is what Kevin Deal at Upscale has to say about tube life:

How do I know when my tubes need replacing?

Power tubes like EL34’s and KT88’s are good for about 2500 hours or more. But may go longer in an amplifier with a conservative design. Small signal tubes with numbers like 12AX7, 12AU7, and 6922, and rectifier tubes like 5AR4 may go 10,000 hours. So you get years and years of enjoyment. Using a tube tester may or may not tell you if you need a replacement. The best approach is to buy a new set of tubes, and install them. If they don’t sound a lot better, put in the old ones and suck every bit of life out of them.


Just replaced the tubes in my BHK preamp for the first time, which had 1499 hrs on them. With no warm-up, on brand new stock tubes purchased from PSA, I heard an immediate improvement across the board. Mostly the music was more energized with better pace and rhythm, and attack. Also I remember the first time I replaced the tubes in my BHK 250, which had around a 1000 hrs on it, I noticed a similar improvement. Considering the relatively low cost of the stock tubes, I plan on replacing them every 1000 hrs. Since I purchased the amp before the preamp it hasn’t worked out where I replace both sets of tubes at the same time, so I just make note of the counter on the preamp when the amp tubes are replaced.

That is really great to know, given I am in a similar tube time zone as you.
The general consensus has usually been that lower current tubes can last
thousands of hours but you always wonder. Wonder if anyone has had
similar findings with BHK 250/300’s.

Hi Gary,
Congratulations. It is a great feeling to renew the sonics of a system. I replaced the first set at 1000 hours. I reset the preamp counter and intend to test the new pair for 2000 hours.

My preamp uses one input tube per input (it uses them to eliminate a switch between the inputs, so a switching between inputs means slowly lowering the one and rising the voltage of the other tube). So I’m able to just plug the signal cable of a source to another so far unused input with a fresh tube and try the corresponding tube against the previous one to find out if it’s worn.

A year for me means probably 1500-2000 hours of use. I think certain input tubes (as well as the output tubes) must have near 10.000 hours. No difference so far (Phillips 6922 military input tubes). Same with a previous preamp using 12AX7 NOS tubes.

That’s why I always wondered what could be the reason within the component design or tube choice for a necessary switch of input tubes every 1000 hours.

In my eperience in my all tubed system new production 9 pin tubes rarely deliver more than half the life that NOS tubes do, and often even less.


To evaluate preamp tubes, I use the headphones amp connected directly to the phono stage or to the DAC and contrast that against the sound post preamp.

If we eliminate from the discussion, tube failure; not working or the tube is creating some unpleasant noise, I do what is commonly recommended, which is to periodically (annually for me) substitute some fresh NOS tubes. If they sound better, they stay in. If not the originals go back in.
But I haven’t found repeatable characteristics of tubes losing their mojo.


M1200s also FET only on stand-by? I presume so.

I recently experienced a considerable loss of high frequencies (accompanied with slightly muddy bass) in my BHK preamp with a platinum grade matched pair of NOS Telefunken E88CC’s with only 940 hours on them. I had even burned them in for the first ten hours @4ma Voltage before changing to the 5ma setting. Very disappointing for an $800 set of tubes which I was expecting to get 5,000-10,000 hours out of to justify their cost.

After this experience, I have decided to not use my hoard of premium $$$ NOS (6v & 7v) tubes for daily listening (4-6hrs.), but to preserve them by limiting their use to occasional “special listening sessions”.