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BIG BROTHER is watching your tubes!


“Owing to the nature of the manufacturing process, tubes exhibit tolerances in the double-digit percentage range; a tube with markedly diverging parameters performs better in some circuits and worse in others.” Source: Wikipedia (German version)

As discussed in the previous blog and as the above Wikipedia quote would confirm, tubes are components that merit some attention. If the right steps are taken – for example, VTI selection, matching, electronic monitoring and visual inspection – there is no better means of amplifying a guitar’s signal. Tubes deliver to-die-for tone like no other component, and that’s a fact. Of course, not every guitarist is also a technician with a firm grasp on all things tube. It takes a healthy helping of expertise to dig into tube technology with tools in hand. Dialing in the perfect bias point while minimizing hum are tasks that the savvy six-string slinger has always delegated to experienced professionals, and there’s no reason to stop now.

“What if the amp itself or a built-in ancillary circuit would be able to constantly monitor the tubes’ status and adjust whatever needs tweaking? What if it could regulate the bias current on the fly?”

We asked ourselves a question much like this after coming up with the VTI system mentioned in our previous post. Back in the day, we were thinking about stability. A little helper circuit would certainly do a lot for that cause. If we could shoehorn a tiny tube tech into the amp, this little guy would make tube maintenance an exercise in convenience. The fact that tubes’ tolerances fluctuate wildly, by as much as double-digit percentages, wasn’t lost on us either. Clearly, tubes need more TLC – tender loving care, that is. And so the idea for the TSC system was born.

There was another very good reason to contemplate the notion of a native surveillance system. The way tubes are designed and built, their operating points and other parameters are unlikely to remain the same forever. Life ain’t easy for tubes. Internal temperature fluctuations can easily run up to several hundred degrees. High operating voltages can range up to 600V. Impurities can infiltrate during assembly before the glass envelope is sealed. All this can do a number on a tube. Then there’s the speaker cabinet to consider. It can move serious air. Those vibrations may be good for you, but less so for tubes inside an amp head typically perched on top of that cab. They rattle the stuff inside, and components don’t thrive on such rough treatment. Fatigue sets in over time. We had all that in mind when we set out to develop the TSC (Tube Safety Control) system that is now integrated into the amplifier circuit to monitor the tube’s main parameters and regulate flows when needed. It’s autonomous and works unobtrusively in the background. Like the doctor promised, you won’t feel a thing. And you don’t even have to do anything but kick back and enjoy as it toils away to keep the bias point of each power tube at the sweet spot. Its impact on the amp’s tonal stability and operating reliability is significant. And if you want to view the tubes’ status on a no-nonsense LED matrix, simply direct your fingertip to the semi-secluded button on the back of the power amp.

A look at the TSC system on the Hughes & Kettner Switchblade: As you can see, there’s nothing to be seen. Well, not much: The four LEDs and the narrow slot next door are the only outward signs that this is where the TSC system works.

A look at the TSC system on the Hughes & Kettner Switchblade: As you can see, there’s nothing to be seen. Well, not much: The four LEDs and the narrow slot next door are the only outward signs that this is where the TSC system works.

The first amp to benefit from this development was the Switchblade TSC. Revamped and upgraded with this surveillance and regulatory system, it was presented to the audience at the 2009 Frankfurt Musikmesse. To say it wowed the crowd is an understatement. Here was a paradox – an innovation in amplification, a revolution in tube tone even, yet there was nothing to be heard. In fact, the TSC system couldn’t be heard even when it took a defective tube out of service. The 100-watt Switchblade is equipped with four EL34 tubes, so when one malfunctions, the TSC system simply switches off a pair of tubes while other the pair picks up the slack. The volume dips marginally at most, so the player can keep right on playing. Our engineers’ enthusiasm reliability borders on obsession, so they soon started talking about making the TSC part of every tube amp. This kind of surveillance/assistance system is a mainstay in automobiles, but unprecedented in tube amplifiers. In hindsight, we couldn’t have made a better move than rolling out this monitoring wizard, the TSC, which some marketer half-jokingly calls “your on-board tube technician.”



Who knows what the future holds in store for the vacuum tube? That they still exist at all is owed, curiously enough, to a large degree to the Cold War. As the story goes, only tube-based electronics can withstand the electromagnetic pulse (EMP) unleashed by a nuclear strike. Whereas computers and digital electronics would all be wiped out, a tube amp would continue to hum along happily, unimpaired by this burst of electromagnetic energy. Perhaps this is why Russia and China, especially, continued advancing the cause of tube technology well into the ‘80s. Today tubes are produced only at coordinates far to the east of St. Wendel. The only major customers for tubes apart from the military are companies that make guitar amplifiers and the few remaining manufacturers of obscenely expensive hi-fi gear for audiophiles.


First published: May 30 2014. Most recent update: October 16 2015.

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Leave a comment

Tim on May 20, 2018 Reply

I just purchased a gm deluxe 40 and find that in standby mode you can still hear hissing through speaker and get feedback from guitar while volume is on. All other tube amps I have when on standby it cuts all sound. Is there something wrong with my deluxe 40?

    Hughes & Kettner Hughes & Kettner on June 4, 2018 Reply

    Hi Tim. Hmm, it depends: part of the transformer’s design in our Meister amps means there will always be a bit of noise when the amp is on Standby. If it’s concerning you though, or is too loud to be a by-product of the transformer, you should have the store where you got the amp take a look at it for you, just in case, and to ease your doubts.

Emma on November 16, 2016 Reply

I absolutely love my Hughes and Kettner amp and having the TSC is really reassuring. Good work guys.

    Hughes & Kettner Hughes & Kettner on November 21, 2016 Reply

    Thanks Emma! Rock on 🙂

john benaers on November 8, 2016 Reply

another printed circuit piece of junk

    Hughes & Kettner Hughes & Kettner on November 15, 2016 Reply

    Well, everyone’s entitled to their own opinion of course, but we respectfully disagree John 😉 We defy 99.99% of guitarists to tell the difference in a listening test…