Dumb question (I think)

PAGS

Super Member
Does anyone roll tubes with power running through the amp/pre-amp? Or put another way, is doing so a really bad idea?
 
I prefer to shut things down before changing tubes. For one thing, you're likely to get nasty noises through your speakers while removing and installing tubes. Also, tubes tend to get VERY hot when operating, and it's hard to not get burned while pulling them unless you have an old-fashioned tube puller. Removing a tube while the amp is turned on isn't automatically going to blow something up, but the speakers might not be too happy about it, so it's probably a good idea to not take chances in that regard.
-Adam
 
I don't think pulling tubes is harmful, but I still don't do it often cause there can be a pop.

I think unplugging a tube is better than short cycling an amp.
 
Swapping tubes while powered on may not be good for the tube (s) being inserted into a up-to-temperature heater string. I prefer to turn off, wait a minute, do the substitution, then turn it back on. Then they can all warm up simultaneously, without shocking the filament of the new tube along with the rest ( like the series/parallel heater string in some fisher units). Just my 2 bits worth...
 
I made a switching device that keeps the heaters on both tubes running, but switches the other connections from each tube to hear the sonic differences in real time. Prior to that, I would pull tubes while powered up, but there would be that wait for the filiment to heat and discerning the sound differences was a lot more difficult. That said though, I've never damaged an amp, tube or speakers doing so.
 
1. The only dumb question is the one you don't ask.

2. Rolling tubes while the amp is on is not, in my opinion, a smart thing to do. I know the old TV techs used to do it all the time but we want our tubes to live a long life. Plugging in a tube with cold cathode, cold heaters, cold grid puts full B+ on the anode before the tube is wared up enough to conduct. There is a great deal of debate on whether that shortens the life of the tube or not. Why take the risk?

3. Pulling a hot tube runs a minor burn risk, not too serious but very not pleasant as well.

Just my thoughts on the issue.

Shelly_D
 
My Fisher has several sections to the power supply to provide different B+ to different tubes. If I pull one tube out the voltages go all whacko and it concerns me that it might not be good for the other tubes.
 
With some direct coupling design, especially with amplifier, removing a driver tube could lead to a run away of the power tubes.
To avoid at all cost.
 
Swapping tubes while powered on may not be good for the tube (s) being inserted into a up-to-temperature heater string. I prefer to turn off, wait a minute, do the substitution, then turn it back on. Then they can all warm up simultaneously, without shocking the filament of the new tube along with the rest ( like the series/parallel heater string in some fisher units). Just my 2 bits worth...
This is a good point. There are certain tubes which do not like being unplugged and plugged in while current is applied, though they're not used much in audio gear. Namely, the 1.4V filament tubes used in Zenith TransOceanics and other portable tube radios. In their case, you run the risk of popping the fragile filament. Not nearly as much of a concern with the (usually) more robust sort of filaments used in most audio tubes, but something to think about, nonetheless.
-Adam
 
I think it's a bad idea. For the tubes and for you. Reasons for the tube are given above. Reasons for you: apart from a heat burn, you might touch another part of the live HT supply, as tube sockets can be tight. When I'm doing testing, the chassis is often partly disassembled.

I suppose a hot swap is possible if everything else is buttoned up, but then you can't measure anything in the circuit.
 
quick power cycling of tube gear has been known to explode things. you risk the
same pulling a live tube that may have unintended power sequencing issues.
 
:)
Properly maintained equipment shouldn't explode just because you turn it off and then back on. The emphasis is on "properly maintained". Is doing that hard on equipment? Probably, but pulling High Voltage parts out while it is running is definitely hard on equipment. Not advisable IMHO.
:)
 
It's really not a good idea when things are powered up. Aside form the annoyingly loud pop when removing tubes, it shows itself as a very large voltage spike at the output transformer. Plus, I have taken out a grid and cathode resistor when doing this in the past.
 
Does anyone roll tubes with power running through the amp/pre-amp? Or put another way, is doing so a really bad idea?
Extremely bad idea! I had a friend pull out a preamp tube that "wasn't lit" from his Mc240 and it blew four plate chokes. I had a hard time finding equivalent replacements.
 
:)
Properly maintained equipment shouldn't explode just because you turn it off and then back on. The emphasis is on "properly maintained". Is doing that hard on equipment? Probably, but pulling High Voltage parts out while it is running is definitely hard on equipment. Not advisable IMHO.
:)
Some gear just doesn't like to be power-cycled quick (i.e. within a few seconds), even when properly maintained. The electrolytic capaitors in the power supply tend to hold a charge for some time after the amp is switched off, and quickly turning the amp off and then back on may cause a spike. In an amp like the Dynaco ST-70, this could cause the rectifier tube to arc over, which isn't a good thing. Best to shut the amp off and wait several minutes for things to cool before switching it back on.
-Adam
 
tube equipment dates back way before protection circuits were required for SS. none
of the dozen or so tube amps I have ranging from 1960's Dynacos to today's amps
have anything close to even what a cheap SS amp has - like a fuse in the B+ lines.

it is not an issue with well maintained equipment - it is an issue with the design. about
20 years ago there was a rash of articles on adding simple fuses to the B+ line, through
the output transformer taps, through the center tap of the power supply transformer.

if you take a tube amp, maintain it to whatever it requires to prevent a power cycle
issue, then warm it up and power cycle it, often.

sooner or later something will go wrong.

this is less likely to happen on SS amps, even with those with a cheap/simple fuse
in the B+ and/or B- supply lines.

I have 3-5 tube amps and am NOT willing to power cycle them. there are folks who
buy power control units that time delay the re-power-on in case of a black or brown out
just to add time to allow cool-down, electrical drain down, etc.

this might simply be a statement from someone who doesn't have a tube power amp.

and however, if you have actual hands on experience with rapid power cycling of
a tube amp, then I'd like to hear which of all the tube amps this is, I might sell off ALL
my tube amps (4 PP el34 power amps, 2 SE integrateds, 2 tube-based headamps/DACs).
and buy this one-of-a-kind
 
I haven’t heard a tube pop in decades....

It’s best to let tube equipment cool down before touching.....can you imagine a tube bursting in your face and glass getting into your eyes ??? That tube technology will bite you real hard if your not careful...
 
One possible problem is accidentally inserting a tube partilly, with the wrong pins lined up, and ruining tube.
 
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