Quick Review of the Monoprice 50 watt hybrid tube amp.

[KeithL]

With some high-powered designs, like radio transmitters, the tubes are kept hot by leaving the heaters entirely on all the time.
When you do this you are essentially trading one sort of "wear" for another... and whether that is an overall benefit will depend on the tube and operating conditions.
Big power tubes tend to experience a lot of "wear" when you're operating them, while smaller preamp tubes really don't.
In the old days, it was not uncommon to see a preamp that was twenty or thirty years old, and that was run 24/7, with most of its original tubes still in place.
(Other than power tubes, little tubes, while they sometimes failed, really weren't considered to wear out.)

Jan 31, 2017 22:36:43 GMT -5 leonski said:

WHY do tubes fail? I wonder if, when turning off a tube amp, you could IDLE the heaters at about 1/2 voltage? That might extend tube life and should also get near 'instant on'.
Do tubes fail like Incandescent lamps, which fail for me usually when turned 'on'?

Auto bias helps tube life, too. Letting a manual bias setup go or simply never checking it might adversly impact tube life.

Are tube amps better off if left on? I don't know, but I don't think so.

If I lived some place that had a cold winter, I might have a winter amp and a summer amp! Tubes for winter to help keep the place warm.

[jmilton]

The new LED tubes run cool and are rated to last a minimum of 30 years.

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(Sorry, I guess those only apply to the new LED light bulbs. My bad...)

[Boomzilla]

Keith is right, and ALL of these issues can be eliminated by using solid state amps (such as Emotiva's). One statement that Keith made that I still savor is to the effect that accuracy can be had from either transistor or tube circuitry, but the transistor option is much the less expensive!

Cheers - Boom

[leonski]

First, for either SS or Tube, NONE of the Best, top-tier designs using Best practices, materials and vetted designs are 'cheap'.

Some tube designs use Rare NOS tubes of great cost and limitied availability. Pass made a SS amp using VFET transistors which are just as rare.
I think Pass got a semiconductor manufacturer to make a new run of 'em.

Even the venerable MC275 which was first sold in the early 60s is up the the 'Mark VI' version. Compare early to current prices. Be sitting.

The reason I asked about running heaters at 1/2 voltage is I saw an article in Radio And TV Experimenter (anybody remember THAT mag?)
a long time ago and for a simple 4 tube table radio, the modification was basically the addition of a DIODE at the power switch.

[KeithL]

Yes, a diode will give you half power - but it will also give you DC.
(That works OK for AC tube filaments and incandescent bulbs - but would destroy most modern equipment.)

I would also bring up the fact that, while exotic components and designs CAN be very good, that isn't always the case.
Sometimes they're used solely because they're "expensive and exclusive" - and don't actually work any better at all.

This is a big factor with those "rare NOS tubes".
Yes, there are variations between tubes made by different manufacturers, and some modern tubes don't work very well....
However, most of those "rare NOS" tubes are simply rare because there aren't many of them left, and really aren't any better than other, much cheaper, ones.
Back when tubes were actually current technology, the whole idea of tube numbers was that they were interchangeable.
A Telefunken 12AX7 cost, at most, a buck more than a plain old RCA 12AX7 - and nobody claimed to hear any significant difference between them.
In fact, most people would walk into a store and ask for "a 12AX7" - at which point they'd get handed whatever brand happened to be sitting there.

Feb 1, 2017 14:01:43 GMT -5 leonski said:

First, for either SS or Tube, NONE of the Best, top-tier designs using Best practices, materials and vetted designs are 'cheap'.

Some tube designs use Rare NOS tubes of great cost and limitied availability. Pass made a SS amp using VFET transistors which are just as rare.
I think Pass got a semiconductor manufacturer to make a new run of 'em.

Even the venerable MC275 which was first sold in the early 60s is up the the 'Mark VI' version. Compare early to current prices. Be sitting.

The reason I asked about running heaters at 1/2 voltage is I saw an article in Radio And TV Experimenter (anybody remember THAT mag?)
a long time ago and for a simple 4 tube table radio, the modification was basically the addition of a DIODE at the power switch.

[leonski]

IF the heater circuit is AC and you can install a diode on just that circuit, I don't see the harm.
As long as when the main power is switched ON, the diode is removed from the circuit and the heaters get full power.

Agreed about some tubes, though SOME are 'legendary'. Whatever that actually means.

Tube rollers have Worlds Of Fun and argue endlessly about some of the weird or limited production stuff.