Checkup On A Fender Tone Master 100W Head

[headstack]

I have a Fender Tonemaster 100W that I am running @ 16 Ohms through the EVM-12L in my Deluxe.

It runs hot enough that it is pretty uncomfortable to touch the standby and power switches.

Do these typically run this hot?

My other question is about longevity and cycling.

My thoughts on long term life of audio equipment is to leave it on if you are using it every or nearly every day.

This has certainly held true for all my studio outboard equipment, consoles, tape machines etc., but I have been wondering as of late on leaving HOT amps running 24/7.

Will they cook themselves silly, or will they be more likely to fail due to cycling induced fatigue.

I appreciate any thoughts on the matter.

John

[Steve Conner]

Like many other Fender amps, the Tonemaster is a "tubes down" design. The hot air from the tubes tends to rise up and cook the chassis. And being a 100W amp, there is plenty of hot air. So yes, you would expect it to run pretty hot.

With tube equipment, you're always going to have a compromise between thermal cycling and just plain cooking to death, as you pointed out. My personal tradeoff is that I'll switch it on when I first want to use it, then leave it on until I'm done with it for the day, although it depends somewhat on the number and value of the tubes. I would carefully warm up and warm down a hi-fi rig stuffed with a matched quad of GEC KT88s, but with a practice amp containing one Russian EL84, I would just flip it on and off whenever I wanted to play.

Especially with vintage tube gear, I'd think twice before leaving it running overnight or unattended. There is always the risk of it malfunctioning and setting the place on fire.

[headstack]

Steve,
Now that you mention it, I wish Leo built the heads with the chassis on the bottom of the box.

As the pesky old devil of thermodynamics would have it, heat rises...
It just isn't fair!!

Actually, the only amp I leave on is my crummy little VOX AC-4TV which has a massive 12-ax7 for power, lol.

That way I can grab a guitar an start playing to any old TV commercial that strikes my fancy.

That's what the TV is for in Vox right?

Vox AC for TV

Thanks for your thoughts, and wish I had those KT88s

In fact, I am a little miffed that I never stocked up on tubes when I began recording, 30 years ago.

GE 6L6-GC Coke Bottles used to cost me $16 a pair from a shop within walking distance from a studio I teched and engineered at.

12-AT and AU7 from GE or Sylvania were $3-$4 and Telefunkens were not a whole lot more.

$1,000 would have supplied me with a lifetime of everything I ever use.

I could easily spend that just doing a retube on the stuff I have if I wanted to use all super nice NOS.

The prices have gotten ridiculous!

[Enzo]

Yes, the hanging tube format tends to run hotter than tubes up versions. But Fender has been making them by the thousands for 60 years or so, and so far they seem to work. I can;t say the heads (tubes up) last any longer than combos (tubes down). it is one thing to expect greater life "on paper," but yet another to expect it in real life.

Now to your unit. Have you checked the bias? The idle current? They all run hat to the touch, but yours may be running a lot hotter than it needs to.


My opinion on turning it off: I think you are overthinking it. What mechanism of failure is your concern? Cycling of the filaments causing one to burn out? In my last 28 years running a pro audio shop, I can count on my appendages the number of tubes with an open heater I have encountered. If you leave gear on it no longer thermally cycles, but it also now is spending HOURS more time at operating heat levels. Cap life is measured at temperature. The longer you leave a cap sitting at 85 degrees, the less time it has left. The cap doesn't care about cycling. The only thing in a tube amp that cares about cycling at all, I would think, was the tubes, and usually we are replacing them for loss of tone before we encounter tube failure.