Letting a tube amp idle...Punishable offense?

[gadget73]

Cathode fuses will only open the output tube circuit. Have to be careful that all of the rest of the caps can deal with full mostly-unloaded power supply voltage if you do this. It also won't do anything for shorted filter caps.

Fuses on the power input are a must IMO. A lot of old gear has no fuse, and its among the first things I add.

 

[mjw21a]

I believe tube life will come down to whether the amp is class A or AB.... Class A will have the tubes running flat out all the time, whereas AB generally has longer tube life.... It may be more complex than that though that's as I understand it.

 

[Bucky Badger]

 

[sqlsavior]

I used to leave my PrimaLuna power amp on a lot. One day when no music was playing I heard a sudden loud hum, and rushed in to turn things off quickly enough to see the puff of magic smoke. They are supposed to be easy on tubes, and very reliable, with several protection circuits, bad tube indicators, etc.

Poof.

 

[Legrace]

In the beginning I wouldn't dare leave my monoblocks unattended for even a few minutes. More then once I returned and one amp was dead, fuse blown and usually a tube as well. Red plating was a common occurrence. I felt I had made a huge mistake getting into tubes.

But now with the addition of a bucker transformer I have no worries anymore, even with absences of several hours. When I come back both amps are always glowing calmly. Zero red plates since. I now have a much better appreciation for the importance of proper safeguards with tube gear, particularly protections against over voltage. Also added a GFI.

 

[maxhifi]

Cathode fuses will only open the output tube circuit. Have to be careful that all of the rest of the caps can deal with full mostly-unloaded power supply voltage if you do this. It also won't do anything for shorted filter caps.

Fuses on the power input are a must IMO. A lot of old gear has no fuse, and its among the first things I add.

The cathode fuses will protect the output transformers from a shorted tube. The power transformer is protected by the primary fuse. Obviously, if the caps aren't rated for the unloaded power supply voltage, it isn't a very conservative design. If a cap shorts, it will either take out the rectifier, or if there's an SS rectifier, it will cause the primary fuse to blow. The real advantages of fusing the cathodes, are that you get a spot to measure cathode current for biasing, and also, you can use a low voltage rated fuse. Fusing the B+ properly involves fuses and fuse holders which aren't commonly available.

From a safety perspective, a fuse on the power input is ideal - think about it, if you have a 3A fuse for example, you're limiting the amplifier to 3A of fault current. In the worst case, it can consume 360W before the fuse blows. Chances are, if the chassis is laid out well, nothing is actually going to get hot enough to start a fire with only 360W available. Maybe it can make a bit of smoke, or get hot to the touch, but there won't be a house fire. The real danger here is for people who locate a tube amp in a location where heat can build up, and it's near combustibles. When placing a tube amp, if you put it on a non combustible surface, in open air, the chances of it actually starting a fire are very very slim - after all, a fire needs an ignition source, and it needs fuel. A well fused amp sitting on a metal shelf, with lots of open air around it has neither. If I don't trust an amp for whatever reason, I just put some bricks under it... you could have a barbeque operating on top of bricks and it wouldn't actually cause a fire.

 

[SaturationPt]

Mine sit on cherry, if it burns I want it to smell nice.

 

[maxhifi]

Mine sit on cherry, if it burns I want it to smell nice.

That Mac in your avatar will never start the shelf on fire, come on

 

[Djcoolray]

Some people believe that there are only so many hours of usage for using tubes, those of us that are using fifty year old tubes believe that tube life is dependent on how many heat up to cool down cycles are experienced. Principles of metallurgy says that the heating up and cooling process severely degrades metal and makes it brittle which is why a stereo components sound output changes over time. In all the time prior to SS becoming popular, I’ve never known tube radios that were left on while sitting on top of the frig to catch on fire and those old tube radios were made from wood. So of the world that relied on tubes.....fire was not an issue.

When tubes burn out they are like a switch turning the circuit off....

What’s to be afraid of but fear itself !!!!

 

[SaturationPt]

That Mac in your avatar will never start the shelf on fire, come on

My British tube amp OTOH, sits on a slate slab. No fire (yet) but oddly enough it also doesn't leak oil.

I think that what I've learned from this thread is: leaving good tube amps on, with proper fusing and reliable power, not a concern. Leaving a cheap power strip on the carpet, can burn the house.

Joking a bit there, but it seems that ever since UL became involved it is uncommon for audio equipment to cause shocks or fires when un-modified, tube or SS.

Leaving an amp idling is better than power-cycling in many cases, if I am going to watch a show or movie with my wife I might let my audio system on without any music, then go back to it later. If I turn off the lights I'll see pilots and tubes glowing, so I never go to bed or leave the house with the amps running (SS or tubes), just seems like the careful thing to do.

I have considered adding a standby switch so that I can leave the tubes hot with no HV, but it can be complicated depending on the amp, so not yet. A lot of instrument amps are set up this way and are left on permanently.

 

[maxhifi]

My British tube amp OTOH, sits on a slate slab. No fire (yet) but oddly enough it also doesn't leak oil.
.

I actually have had old RCA theater amps leak oil, when the old PIO capacitors gave up the ghost

You're right about the UL. Some of my earlier DIY amps sure wouldn't pass UL - I've gone back and added safety features to some of the stuff I built in the 90s. Back then my attitude was leave out anything which doesn't improve performance.

 

[gadget73]

I had a National shortwave set that required an oil change. PIO caps had blown gaskets, the inside of that thing was a mess.

 

[Rockon1]

Wow I guess Hi Fi tube amps are more finicky than guitar tube amps? Not one of the 11 guitar amps I have would I concern myself with leaving on and walking away from. Power tube failure(shorted) has been fairly rare for me over the last 30 years. If they get past "infant mortality" they seem good to go mostly until they wear out- which is a long time. Admittedly I keep an eye on new tubes for a bit for that reason. I may be lucky but on top of that not one blown OT, PT, Capacitor,resistor. Preamp tubes are another story. Plenty that have been rattled into microphonic submission, lol.

 

[gadget73]

personally I don't fuss about it too much, but I don't leave things on for days at a time either. At least not on purpose. I did once leave a preamp on for about a week, it didn't blow up. I don't do this with gear that hasn't been overhauled or that doesn't have a fuse though.

 

[Ratamacue]

I'm not an EE and know only basic electronic stuff but are you to be that worried about leaving gear on if you turn your back for a minute? People post on both extremes of the spectrum on this topic so its really hard to get an idea of what is a proper recommendation. I suppose this is no diff than any other topic in this hobby.

Most of the responses seem to be with regards to amps, are pre-amps any different? I am brand new to tubes and just received a new pre (Atma driving Pass mono's) and on weekends, where the bulk of all my listening is done, I would usually fire everything up in the AM and turn off before bed at midnight'ish. Seemed silly to turn rig on and off several times a day.

 

[ducati_EL34]

I'm not an EE and know only basic electronic stuff but are you to be that worried about leaving gear on if you turn your back for a minute? People post on both extremes of the spectrum on this topic so its really hard to get an idea of what is a proper recommendation. I suppose this is no diff than any other topic in this hobby.

Most of the responses seem to be with regards to amps, are pre-amps any different? I am brand new to tubes and just received a new pre (Atma driving Pass mono's) and on weekends, where the bulk of all my listening is done, I would usually fire everything up in the AM and turn off before bed at midnight'ish. Seemed silly to turn rig on and off several times a day.

Some people are coming to tube equipment a little late. Just remember the adults who owned this equipment back in the 50s and 60s, did not fret over leaving equipment on, except maybe to prolong tube life. They were frugal in that way.

Tube equipment that is new or refurbed is no more of a safety hazard than SS equipment, all things being equal. Just make sure your tube equipment has plenty of good ventilation.

 

[Ratamacue]

Some people are coming to tube equipment a little late. Just remember the adults who owned this equipment back in the 50s and 60s, did not fret over leaving equipment on, except maybe to prolong tube life. They were frugal in that way.

Tube equipment that is new or refurbed is no more of a safety hazard than SS equipment, all things being equal. Just make sure your tube equipment has plenty of good ventilation.

Yeah I kinda figured as much. Everyone has their own experiences that forms ones experience and thus opinion etc.. It just seems like any well made, solid engineered product "should" be robust enough to not worry sooo much about things. Certainly there are exceptions, and common sense with proper usage goes without saying.

I'm pretty excited (to put it mildly) to get my new pre and tube journey on their way

 

[Blasty]

My power amps were built with the intent that they would outlast me and do so under heavy use. They are on nearly all the time whenever anyone is home. I over-spec'd everything and the tubes are run a bit on the conservative side. I included primary and secondary fuses sized at 125% of the current ratings for the windings that they protect. Finally, the amps have closed covers on the bottoms (no holes for burning material to fall through) and cages on top (cat proof).

I would be confident to leave these on 24/7 were I not concerned about burning through my nice old tubes, even though I'm fully aware that power cycling has its own detriments as discussed already.

My phono preamp, however, was an exercise in compact building which I am very satisfied with performance-wise, but I prefer not leave it on when not in use. 4 tubes including rectifier are packed into a tiny case along with a few watts of dissipation from resistors, and it runs fairly warm. This one is only fused on the primary, so there is a greater chance that a fault could burn something up before it blows.

So, it varies. Personally, I avoid running any tube gear unattended unless it is something that I built to be absolutely safe or have gone through completely and updated, and is not running any component on the edge of its rating.

 

[noogies]

I don't think any of us would leave a tube amp on, then go on vacation, but, is there anything wrong with stopping a track to go do something for an hour or so and leaving the amp all nice and warmed up to come back to?
Flame away!!!

Does the room you keep it in need heating?

 

[bbqjoe]

Does the room you keep it in need heating?

Yes!