Snap, crackle, pop …

[AnotherJohnson]

We don’t often get questions about these kinds of noises in tube amps.

They come from a failing small tube rather than from a failing power tube.

Yesterday, after about 42 months in service, I put on a new CD, sat down to listen, and was accosted by random ticks and pops in the left channel. I wondered if the CD were defective, and approached the CD player.

When I went by the left speaker, I could hear a low level hiss and crackle. I stopped wondering about the new CD. Instead I shut the system down, waited for the tubes to cool a bit, took off the guarding plexiglas, pulled the three 6922s, replaced them with new from my supply of spares, sat back down, and tried again. Of course it was perfect.

The three pulled tubes went straight to the trash. I do not want to get them mixed in with my stock of new tubes and pick one out later thinking that it’s new.

42 months is a long enough life. There’s probably just one that’s done … but the others would follow soon enough, and I value my speakers enough to worry about how loud some of the pops can be as a small tube finally knuckles under to its age. This would be a non issue with McIntosh amps since they include controls to clamp the maximum spike that can be passed to the speakers. But to my ears, this internal electronic police force affects the way the amp sounds, so I stick with CJ.

My only debate is whether or not to go on and replace the 6922s on the right amp too. And, whether or not to go ahead and replace all the KT120’s while I’m at it. I’ve got the spares on the shelf. It would be safer than to wait for failure. Preventative maintenance is a good practice and 42 months is a long run for a set of tubes. At Upscale prices, it’s less than $25/month. That’s cheaper than a high end LOMC phono cartridge.

[admin]

The 6922's are inexpensive so that I think is a no brainer. As for the KT120's, those are more expensive. As you know (and much because of your advice), I decided to buy a complete new set of KT120's for my ART amp when I had one of them fail late last year.

[AnotherJohnson]

I am going to go ahead and R&R all the tubes when I’m back there in a few days. I had not realized that it had been 42 months since those tubes went into service until I looked at my tube maintenance log for that amp after the event.

[roberto]

I had a lot small tubes failure. Specially E-88CC made in Holland. The Genalex special edition 6922 (gold pins and super low noise) is now sounding in my preamp and power amp. I have a very good signal to noise ratio them.

[AnotherJohnson]

In a preamp, crackle and hiss seem to be the giveaways.

But in the early stage of a power amp …. OH BOY! That snap can turn into a driver killer.

[roberto]

Yup, full power would be possible for that crackle.

[AnotherJohnson]

That’s really the best argument for NOT breaking things in by turning them on and walking away. I am wondering about that habit now that my speakers are in the five figure range. It’s all relative I suppose.

If either a small tube or a power tube were to fail, depending on the fusing and the failure mode, it could be costly if not shut down by the listener. No listener? Greater risk.

I’ve had exactly one power tube runaway on me … and I was present… but the previous owner of the amp had fused it wrong, so I got to experience the full effect while diving for the power plug to shut it down. This may be at the heart of my tendency to R&R power tubes before there’s a failure.

I’ve had several small tube failures in both amps and preamps. These usually manifest as an increase in the noise floor, but twice I’ve had the loud popping in a power amp channel come first. Potential driver damage scares me … because I had a solid state failure once that did totally blow out drivers. Solid state will typically go longer between failures … but when solid state fails, it often makes an even bigger and more expensive mess to deal with.

[AnotherJohnson]

This potential driver failure issue has always been McIntosh’s argument for their output power management circuitry. I’ve heard the pitch (being given from salesman to a customer) many times. The example of an amp failure blowing up a speaker is emphasized as a near certainty for any amp without the McIntosh features. In my experience, it’s a rarity, but the probability is not 0.

[roberto]

Again, I am with you AJ,

SS repairs are more expensive than tube repairs. Also, usually on tubes, the user can do the repair. Changing a bad tube is not a big deal.

When the SS output stage fails, usually a symmetrical complementary stage (NPN-PNP) and quasi-symmetrical complementary stage (NPN-NPN) using darlington NPN transistors is the most common circuit design. The quasi-darliington NPN stage usually is used for Class A power circuit design.

When these stages, a transistor fails and before the protection circuit acts, an excessive current pass through these output transistors, making them to fail too. Some might have collector current leakage and the measurements might look right, but it is better to change them all. Expensive process.

The CMOS FET transistors, its behaviour is like a tube...CJ used a lot of cmos-fet and bipolar transistors in their output stages.

Noisy tubes usually is related to the small tubes. And red plates are related to power output tubes. If you see an all red power tube, turn off the power amp, and change it! WAIT SOME TIME because that tube is going to burn your fingers.

It is wise to wait some time, if you are going to take any vacuum tube out of its socket.

Happy listening!