[cheap-Jack]

Hi.

If a power tube fails catastrophically, shouldn't a fuse blow before a transformer melts? Sounds like the amp was not designed correctly to me.

It depends on where the fuse is placed. If the fuse, which is usually a 'slow-blow" one, is at the primary winding of the power iron, firework can occur at the powerstage & the O/P iron can be damaged instantly if the power tubes blow as the slow-blow AC fuse react too slow to stop the blow-up.

That's why for power stage employing direct coupling driver-stage-to-power stage topology, a fast-blow fuse should be added the plate circuit of the power tubes. Special bias current/voltage stabilizer should be added at the power tubes circuit to prevent such disaster happen.


c-J
 

[medium jim]

Steve:

While there has been improvement in QC, the metallurgy and inert gases will never be the same due to many factors. However, many of the modern amp, preamp designers are factoring into their designs modern tubes and in such instances, vintage tubes may not be advisable.

I still see no advantage of running tube gear 24/7 and only downsides.

Jim

[macrojack]

As a third party with no commitment to either side of this discussion, I've come away with this observation. One side warns about the potential risks involved in leaving amplifier tubes charged at all times, especially unattended. These people seem to be either well informed about the science involved or permanently chastened by unpleasant personal misfortune.
The other side appears to argue in favor of leaving power amps on 24/7 because they've done so for years with no ill consequences  --- YET!!!

[Steve]

Steve:

While there has been improvement in QC, the metallurgy and inert gases will never be the same due to many factors. However, many of the modern amp, preamp designers are factoring into their designs modern tubes and in such instances, vintage tubes may not be advisable.

I still see no advantage of running tube gear 24/7 and only downsides.

Jim

I was only replying to the insinuation that new tubes do not last long. They can last quite long. I personally power off my components after each use, and power on some 30 minutes to one hour before. So I agree with you.

Cheers.

[Quiet Earth]

I have not been struck by lightning . . . yet. 

[Quiet Earth]

I have not won the lottery yet either.  . But I hear it's possible.

[pansixt]

I ran the same tubes in my amp for 10+ years. This was with moderate use and care
(always giving them 20-30 mins warm up before heavy load).
Only recently did one output tube start surging occasionally, and Dean replaced all of them last week in the U-70 Rebuild. So I plan to continue with the same method going forward.

Sure, I have left my amp powered up all day many times. But never unattended for long, and never 24/7.
Why tempt Fate. A house fire is a scary thing. Kind of like leaving any appliance with a strong heat source on while you (and possibly your family and pets) are asleep.

Having Teenagers in the house while we were asleep was scary enough. 

[Ericus Rex]

I suspect some manufacturers intend for their preamps to be on 24/7.  I used to own a Counterpoint SA-5.1 (all tube, including rectification and voltage regulation - 8 tubes total) that had the power switch (a small flip switch BTW) on the power supply.  That power supply was directed to be kept as far away from the preamp as possible, on the floor was implied.  Mike Elliot is no idiot.  I suspect he assumed most owners would keep the preamp on all the time instead of squating down, reaching behind the rack and turning the unit on and off constantly.  Furthermore, the preamp wouldn't actually turn on the way off.  If the pre was plugged in the heating filaments were lit regardless of the power switch setting.  Now, all his amps, IIRC, have the power switches on the front panels.  'OK to run pres 24/7, but turn amp off when not using' I think is what he's trying to say here.

[JakeJ]

I find it odd this thread is still alive, the OP has either sold his tube gear or figured it out for himself by now.

Common sense does not apply when engineers are involved (98% of the time, anyway).  Leave tube gear on 24/7?  Only if I have extraordinary home owner's insurance.  'Nuff said.

[JerryM]

...the OP has either sold his tube gear or figured it out for himself by now.

Hopefully everything is one piece. 

 

[Ericus Rex]

Threads can, and often do, last beyond the OP's query.  You know that.

[Scott Novak]

Tubes warm up rather quickly.  But it takes a substantial amount of time for transformers and electrolytic capacitors to warm up and stabilize.  In particular, electrolytic capacitors generally perform better when hot.  Keep in mind that electrolytic capacitors are electrochemical devices and chemical reactions speed up as the temperature increases.  As the transformer warms up it's internal resistance increases and it's output voltage drops.  Unless your tube filaments have a regulated power source, the voltage from the power transformer will drop and the corresponding reduction in filament voltage will change the operating characteristics of your tubes.  The B+ will usually drop as well.  So you do need a substantial warm up time for your amplifiers to stabilize.

I performed safety testing on switching power supplies for 6 years, so I have a pretty good idea of what UL testing is all about.  UL approval means that a product is relatively safe, but it's not a guaranty of safety.  The safety agencies only require testing for single component failures.  In real life multiple components can fail and result in a failure that could cause a fire or electrocution hazard.

Does your amplifier even have ANY safety agency approval at all?  I wouldn't want to trust my life of a piece of electronic equipment that didn't have any safety agency approval.

It's not a good idea to leave most tube power amplifiers running unattended. 

Preamplifiers are usually not a problem because the power levels used are much lower and they don't generate so much heat.

Also, people running vintage equipment need to realize that this equipment was designed for lower line voltages than we have today.  Todays higher line voltage results in higher voltage to the filaments and shorter tube life.  So if you haven't done anything to drop the filament voltage to an appropriate level you should be more concerned about running your tubes any longer than you need to.

Scott Novak