• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Turning tube amp off and back on quickly

kahlfin1k

kahlfin1k

Well-Known Member
I've heard that you shouldn't turn a tube amp off and back on right away many times on the web. I'm relatively new to tube stuff and have been fixing a lot more tube stuff lately and it's annoying to wait a few minutes to power cycle something while you're working on it. Also with rolling tubes there's really no way to expect to make any kind of objective decisions after a few minutes of no listening.

So my question is, is this another well meaning but exaggerated over cautious piece of advice? Has anyone actually seen a tube amp damaged by doing this? What are we talking about getting damaged in theory?

Thanks!
 
Register to hide this ad
kahlfin1k said:
I've heard that you shouldn't turn a tube amp off and back on right away many times on the web. I'm relatively new to tube stuff and have been fixing a lot more tube stuff lately and it's annoying to wait a few minutes to power cycle something while you're working on it. Also with rolling tubes there's really no way to expect to make any kind of objective decisions after a few minutes of no listening.

So my question is, is this another well meaning but exaggerated over cautious piece of advice? Has anyone actually seen a tube amp damaged by doing this? What are we talking about getting damaged in theory?

Thanks!
Click to expand...

I'm really no expert here as I've only been dabbling with tube electronics for about 6 years now but theoretically not allowing the tubes to fully warm up before turning them off could cause the filiments (the part of the tubes that glows orange inside your tubes) to catastrophically fail or just burnout period (its kind of like what happens with an incandescent light bulb when you continuously turn it off and on right away.)
 
Lots of threads on this subject, and it has been hashed however I will say that a quick on/off cycle will not really do any damage to the amp itself but tube gear that uses tube rectifiers may flash over on a quick restart and it has even happened to me. It might damage the tube rectifier if you keep doing it and then the tube keeps flashing and won't stop no matter what amplifier you use it in.

I don't own any tube equipment with solid state diodes or rectifiers so I am not sure what kinda damage you could do to the power supply if any but just use some common sense when doing some tube rolling and quick on/off cycles!

I'd say that it's safe to say to wait about 30 seconds to one minute in between power ups and things should be ok.

How does one really roll tubes if one doesn't have the patients to wait 30 seconds with each tube swap?
 
Last edited:
cademan said:
Lots of threads on this subject, and it has been hashed however I will say that a quick on/off cycle will not really do any damage to the amp itself but tube gear that uses tube rectifiers may flash over on a quick restart and it has even happened to me. It might damage the tube rectifier if you keep doing it and then the tube keeps flashing and won't stop no matter what amplifier you use it in.

I don't own any tube equipment with solid state diodes or rectifiers so I am not sure what kinda damage you could do to the power supply if any but just use some common sense when doing some tube rolling and quick on/off cycles!

I's say that it's safe to say to wait about 30 seconds to one minute in between power ups and things should be ok.

How does one really roll tubes if one doesn't have the patients to wait 30 seconds with each tube swap?
Click to expand...

I'm not talking about 30 seconds more like 3 minutes. It's difficult to make objective judgements after waiting a while.

Sent from my ADR6300 using Tapatalk 2
 
I avoid quick turn off and on - I've burned out too many rectifiers by doing this - since I've been careful - I haven't lost a single one. You will likely find out as I have - the hard way.
 
If you are being honest/truly objective with yourself, you can't make comparisons unless the tubes you are quickly throwing in the amp are preheated. You are fooling yourself if you think that cold tubes are a good comparison to warmed up tubes, so what does it really matter? You aren't interested in a real apples to apples comparisons, so do as you please......
 
For DECADES, tube equipment survived, IF.... it was well-designed.
Tubes are forgiving creatures, always were.
So with that said, if you're having an issue with something, it then has design flaws - but don't listen to internet blabber, just because it's posted somewhere, by somebody that started a "wive's tale" about their particular instance.
 
The equipment may survive, but rectifier flash is real, and I've had to replace rectifiers myself. This one isn't just internet blabber.

A rectifier tube may survive once or twice, but why take the chance?
 
I have personally seen damage happen in certain hybrid amps of mine from ''hot swapping '' driver tubes-powered down but didn't wait long enough-yes-it's true.
 
I think the problem is caused if the rectifier tube is still hot enough to conduct when the unit is switched on, and the filter caps is completely discharged,there is too much inrush current for the tube to handle.It puts quite a strain on the transformer,and possibly choke.Sometimes it will blow a fuse in this situation.
 
You guys need to quantify "quickly". I read the original post as meaning a few seconds. The OP later clarified he was meaning several minutes.

I know I've seen rectifier flash when off-on was a few seconds. I don't recall seeing it if off-on was several minutes. Im pretty sure I've turned amps back on many times within a couple minutes after swapping speakers. Not that its right, just my experience.
 
Its true

I have smoked a rec tube by accidently turning on the amp to fast. Good rec tubes are not cheap either! :no:Matter of fact, I have heard it is good practice to have tube amps plugged into a battery backup in case of a quick on/off power outage. Course I don't have mine plugged into one. Couldn't hurt though IMHO.
J.T.
 
When I am working on an amplifier and I want to turn it on and off quickly I will have a back up rectifier waiting and yank the hot one and put it aside, then I check that the b+ is drained off which is very quick because all the other tubes are still lit drawing power. Then I will do the modification I need to do and plug in a cold back up rectifier into the socket. Its a crude stand-by switch. The only thing on in the amp with the rectifier out is the filament and maybe the bias supply. Or you can add a temporary stand-by switch, just make sure all the connections are insulated so you dont grab the switch and get a big shock!
 
kahlfin1k said:
it's annoying to wait a few minutes

So my question is, is this another well meaning but exaggerated over cautious piece of advice? Has anyone actually seen a tube amp damaged by doing this? What are we talking about getting damaged in theory?

Thanks!
Click to expand...

He was asking why he had to wait,and if the info was real.
I think 1 1/2 to 2 minutes would be enough time to cool down.
 
Last edited:
There are enough answers already so I won't throw another opinion in the mix but I would opine...

A nice "quick" a/b can be useful in some cases but for the most part I listen to music for long periods of time so I test for a long period of time. I will either grow to like the difference or it goes the other way.

A real short a/b would be much easier at revealing minor differences that memory would mask but what I think I like the most in those quick tests may not hold up long term.
 
Threat is real - you're risking catching your amp on fire, or worse. Ask your house mates if you should wait 2 minutes or risk burning down the house.

There are solutions tho...

one is to add 2 UF4007 diodes in front of the rectifier tube.

Another is to add a CL-90 to the center tap on the HV secondary

CL-90 will be warmed up tho on a fast hot start and wont slow down the turn on, the diodes will keep the short circuit (arc over on rectifier) from reaching your power transformer.

What happens on a hot start the PSU caps will discharge cause all your tubes are in place live circuit has plenty of resistance to bleed off the caps. On hot start the PSU FIRST ac cycle will cause over current for your rectifier as that initial charge on the capacitors will be significant enough to cause arc over.

The first and only time I had that happen was when I said to myself "it's only this one time"; turned my amp back after hot start and poof amp up in smoke and fire. Yea it happens. The fuse is there to keep the short circuit condition from entering your house wires, wont protect the amp or transformers.

Why risk it, take a walk and get a drink of water or tea let the amp cool down, it will only take 2 minutes or so. I can't imagine any situation where by I risk a fire OR wait 2 minutes... kinda a no brainier there.

Hot start your grill or your fire place not your tube gear!!:thmbsp:

Even with SS gear I don't hot start...

Cheers,
Bob
 
Well, I've always believed in the no hot start dogma, but I've also seen Dennis Had hot start his amps with impunity and complete lack of concern. However, he also leaves his amps for hours at a time with no load. I guess if you really know what you're doing, it's all good. I have also done some voltage measurements with a CL-90 in line, and I was surprised how slow the voltage ramps up, even with a short start.
 
Speaking from my own experience with a McIntosh MC 240, I can attest the amplifier does NOT like being switched off and on rapidly again once the amplifier has achieved full warmup.

Twice it has resulted in blowing a 6L6 and fuse. (The second time was non intentional).

This model is designed with a thermistor which is heat sensitive, preventing high current rush when cold. It seems to take somewhere around a minute for the thermistor to cool down sufficiently before starting up the amplifier again to prevent any damage.

I have the amp plugged into a relay distribution box that delays shutoff for 30 seconds to prevent this from happening should the power be interrupted or if the power is accidently turned off so that this will not occur should power be briefly interrupted for whatever reason.

The tube preamplifier I have does not seem to protest in the manner as the amplifier does in quick turn off/on situations.

The tube receivers I've owned never blew fuses or tubes as a result of this either but I think waiting a minute or so is not a bad idea.
 
You must log in or register to reply here.
Back
Top Bottom