Can you do anything to make power tubes last longer ?

No… luck as I inherited the MAC which i abused as a young punk… The Music Reference connection born of my experience selling gear Roger designed and built w Harold Beveridge… also imo a genius… RIP….

mulveling,

Could you suggest particular Amperex EL34 that I might want to try later ?

Perhaps, I should also try Sylvania 12AU7 black plates from 50s as well. What difference would they make compared to RCA black plates from 50s, I wonder ?

Mke sure there all biased correctly.enjoy the tube sound.

Found them ! Matched quad of Mullards EL34 XF2 is coming this way. It's a little risky because they are not new and the exact number of hours on them is unknown, though supposed to be low enough. Test as strong NOS, as the seller with excellent feedback says. It's always a gamble with tubes to a degree, I feel fine about it.

Found them ! Matched quad of Mullards EL34 XF2 is coming this way. It’s a little risky because they are not new and the exact number of hours on them is unknown, though supposed to be low enough. Test as strong NOS, as the seller with excellent feedback says. It’s always a gamble with tubes to a degree, I feel fine about it.

Nice! Enjoy - great tubes. Don’t worry about the exact hours on ’em. A meaningless metric, now. "They don’t make ’em like they used too" applies, etc and yada yada...

For Amperex / Hollands I’ve only used the xf4 and xf5 models, both with the brown/red-base. They both sound equally great - I’ve even mixed them in quads (matched pairs), with no problem. The older metal base Philips / Holland version is supposed to be extra special - I’ve almost pulled the trigger on these in the past, but never did.

Perhaps, I should also try Sylvania 12AU7 black plates from 50s as well. What difference would they make compared to RCA black plates from 50s, I wonder ?

Why not? I expect 1950s black plate Sylvanias should be very good. I generally prefer these over any RCAs, though I haven’t tried the 12AU7’s. You can do 5814, 6189 and 5963 subs too. The 5963 tend to be microphonic, so those should be relegated to amp driver slots only (NOT the preamp or phono slots).

RCA black-plate 5963 was the favorite 12AU7 sub for early 2000s-era VAC power amps.

@inna I wouldn't say that I recommend choosing an amp that is easy on tubes so much as I recommend against an amp that is hard on tubes.  How do you know which is which?  

I'd say avoid an amp that gets more power than normally attributed to that tube--unless I needed that power and was willing to buy tubes.   And I'm fine with that. Personally I don't think tubes are expensive compared to the rest of the audio equipment we all have to purchase.  I buy tubes when I don't need them.  A nice pair of Hytron 801As showed up yesterday. 

There is a trend now to make higher power tube amps to drive lower sensitivity speakers.  I like higher sensitivity speakers but if you're married to your 92-95dB speakers and want to drive them with a tube amp, you need more power.  So they are making more push pull, parallel SET, and High power SETs with the higher output tubes.   if you buy some of these, recognize you'll have to replace tubes more often.  (not saying push pull amps are hard on tubes, unless designed that way).

If I'm looking at a 300B SET and the OEM says 8 wpc, and 300b's generally do 6 wpc, I'm going to wonder about tube life.  (or else the marketing talk is exaggerating and it really is a 6 wpc amp).

I've found that if you go with an amp builder with a lot of experience and knowledge, they are likely to design their amps conservatively.  And if you call Aric or Apollo and order and amp, if you tell them to use conservative parameters to promote long tube life, I'm sure they can do that.

jerry

Jerry, you are right.

Anyway, the best way forward is to have more spare tubes !

mulveling, I think I am done with audiophile expenses for this year, But..let me see..maybe I can cut the expenses somewhere else. This is a disaster.

I saw those Sylvania on ebay but I will wait - currently installed RCA black plates from early 50s work very well, no complaints.

Now that I am going to have better Mullards, I suppose I will not accept anything less in the future. It is either XF2 or XF1 Mullard or perhaps Amperex Holland.

@inna For longest tube life:

1) keep the tubes clean and free of fingerprints.

2) keep them biased properly, if you can run them a little below spec. This works only if the sound isn't adversely affected.

3) use the Standby switch to warm up the tubes. If you don't have one on your amp consider getting one installed. A standby switch cuts off the B+ (DC high Voltage) for the tube. As its warming up, if the plate supply Voltage (B+) is present, you get a phenomena called 'cathode stripping' where the cathode coating gets eroded over time. So a standby switch can prevent this.

4) don't push the amp hard. In a class AB amp (most EL34 amps are class AB) the harder you push the amp the hotter the tube gets and heat causes it to wear faster. So make sure your speakers are easy enough to drive that the amp is loafing nearly all the time.

5) make sure you have adequate ventilation. Again, heat is the enemy of the tube.

6) Make sure your speaker is connected to the right output transformer taps. So a 4 Ohm speaker should never be on the 8 Ohm tap; that would cause the load on the power tubes to be much lower, causing some of the power they make to be dissipated in the tube rather than the speaker- so yes, they will run hotter, put out less power and make more distortion.

7) make sure your line Voltage isn't running high. 120V is normal now and the line is not supposed to exceed 125V for more than a second. But I've seen situations were 125V was normal and unsurprisingly the customer was going through power tubes a lot faster.

8) the controversial and last thing: Some amps push power tubes harder than others so go through tubes faster. You might want to take a thermal camera to see how hot the tubes are running and compare that to other EL34-based amps, or use the internet to see if there's a correlation with certain amps that tend to go through tubes faster.

Follow these suggestions and your tubes will last longer.

inna, you can bias amp’s output stage for 20% less current, and use 120<=>110V step down transformer. These two steps will increase tubes life time significantly, est. 30%+. 

Ralph, thank you.

It appears that I do everything right. There is no standby switch. Voltage is regulated by the regenerator, I hope it is. Ventilation is excellent from all sides. The amp seemingly drives the speakers with ease, no stress that I can perceive. The tubes are clean, no fingerprints. I might try to lower the bias a little and see what I hear.

atmasphere

... make sure your line Voltage isn’t running high. 120V is normal now and the line is not supposed to exceed 125V for more than a second. But I’ve seen situations were 125V was normal

If you’re talking about the US, you are mistaken @atmasphere. Nominal voltage in the US is 120VAC $$\pm 5\; percent,\; so\; anything\; between\; 114VAC\; and\; 126VAC\; is\; normal.\; That\; is\; established\; by\; ANSI\; C84.1\; standard.$$

$$Note\; that\; the\; spec\; is\; measured\; at\; the\; service\; entrance\; -\; it’s\; common\; to\; have\; some\; voltage\; drop\; at\; the\; AC\; receptacle.\; That’s\; something\; dedicated\; lines\; can\; help\; limit.$$

What is "normal" is not necessarily ideal for tube electronics, particularly vintage gear that was built for lower voltages that were prevalent when they were made.  As I mentioned above, my local dealer who only sells tube amplification often has customers measure their outlet voltage and then orders the right transformer for them to use on the outlets supplying their amp and other tube gear.  He prefers to run the gear at much lower voltages than is common.  This is usually the cure for premature tube failure.  He also has his customers bias amps on the conservative side.  This is consistent with Atmasphere's recommendation.  

My normal voltage has been, for the longest time very steady at 117 volts at the outlet, but has recently crept up to 119-120.  My amp is cathode biased so I cannot do adjustment, but typically, cathode biasing means conservative levels.  If my voltage rises more than this, I too will consider a transformer.

If you’re talking about the US, you are mistaken @atmasphere. Nominal voltage in the US is 120VAC $$\pm 5\; percent,\; so\; anything\; between\; 114VAC\; and\; 126VAC\; is\; normal.\; That\; is\; established\; by\; ANSI\; C84.1\; standard.$$

@cleeds I stand corrected. 

However if the line Voltage is consistently 126V you'll find that tube life is curtailed with many tube amps and all if they are vintage. 

I recently worked on an Eico tube amp that was 'eating tubes'. The amp was built when '110V' was the norm. The output tubes were conducting way too hard. They were cathode biased so I was able to change the cathode resistors and calm things down. 

The only thing that can come to mind about making your power tubes last longer would be to set their bias a little under than the recommendation for the amplifier. This will not hurt the amp or the tubes in any way. The manufacturer has a recommended set point for where the power tubes should be biased to get the best sound and operation from the amplifier but by adjusting the bias to your liking, you might be happier. And by dropping it down a bit under the recommended set point the tubes with be running a bit cooler and should last a little longer. . Some people choose to run their tubes hotter which burn them out sooner and others run their cooler which makes them last longer. You’ll also hear a difference as you adjust the bias. I’ve experimented with this on my Canary 301 mk 2 300b amplifier yrs ago. 

In other words, I can set the bias as low as I want to until the point when I hear the deterioration of the sound quality. Setting bias by the ear not by manufacturer's recommendation.

The designer and builder of our monoblocks uses the same Dodd Balanced Power Supply to power his builds that we use to supply power to our system. They makes exactly 120 volts at 60 Hz. The 75 lb. laminated core transformer takes whatever comes from the wall outlet and makes a +60v and a -60v rail, both at 60Hz, and then joins them at the outputs. The amps are optimized for KT77 output tubes and can run no other type of output tube. I foolishly tried all of the usual suspects, even though I was told by the designer/builder that it wouldn’t work; he was right, can’t get any other output tube type to bias correctly. Had a lot of Octets for sale for a while :).

Anyhoo, I feel very lucky about the amps being designed and built based on the same power supply; apparently, pretty darn optimal. Accordingly, I’ll say again, for tube amps, it’s worth using a Balanced Power Supply (or, I think, a power regenerator) to assure that your amp(s) see 120v at 60Hz.

It's been a while since I ran amps that required biasing, but my approach was to start at the low end of the builder's recommended range.  Then, in part because I'm lazy and because I want to be gentle on the tube.  I would just leave things be and not bother to check the bias.  As the tube ages, the current flow drops on its own so the bias point drops.  By not changing the bias to compensate for the drop, i am actually preserving the tube, albeit with a small loss in output power.