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Dirty-South Blues Harp forum: wail on! >
Tube ?
Tube ?
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Hobostubs Ashlock
1825 posts
Jun 20, 2012
8:24 PM
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If your going on a short break say 5 min,Is better to turn off a tube amp or just let it stay on,Im asking because A guitar player,once told me it was better on the tubes,To just leave it on,rather than turn it off for a short period,I dont know if he knew what he was talking about or not,and I firgure you guys would shoot me straight,thanks
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Hobostubs
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SuperBee
328 posts
Jun 20, 2012
10:26 PM
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Short break, I would leave it on. There would be a break even point, but I don't know where that is. I'd say 5- 10 minutes would be safe to say better to leave it on. A bit like a light bulb. They don't where out when they're off. Usually a bulb will blow when you switch it on, but they can hang in a long time, ready to blow until you switch off. Sometime you can hear them buzzing and you know Next time you switch on that bulb is gonna go pop. Of course a tube isn't quite like that because in use it's not in a steady state, but you know, it's the wear and tear thing. Anyway, I know there's a line but I don't know where it is. Someone will have an idea, but it will be a bit different for every amp I expect
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Hobostubs Ashlock
1826 posts
Jun 20, 2012
11:33 PM
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thanks superbee
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Hobostubs
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SuperBee
331 posts
Jun 20, 2012
11:44 PM
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I didn't express what I mean very well, but hope you know what I mean. Like the thing that wears them out most is using them to play through. then the next hardest thing on them is switching on an off, then just being switched on but not active, that's what I reckon anyway. You know, like the light in the bathroom is always being switched on and off and that's the lamp that blows most often kinda thing.
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Hobostubs Ashlock
1827 posts
Jun 21, 2012
12:01 AM
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So if Im just going to be taking a 5 or 6 minute break leave them on?and if Im going to not play say 20 min or more, turn them off? (give or take on the numbers)
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Hobostubs
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SuperBee
332 posts
Jun 21, 2012
12:57 AM
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Yeah I dunno where the point is where it's better to turn off. I think that's why they invented standby on the bigger amps. But yeah something like that. It's a complete guess as far as the timeframe, but I think the principle is right. I have no idea how you would go about working it out apart from doing actual test experiments. I don't think you could calculate it because there would be too much variation from tube to tube. You'd have to test heaps of them to get an average life span etc. but I reckon you'd be on the right track with what you suggested above. But hey, sometimes I have forgotten to turn my 2x EL34 amp off for half a day, and I've gigged it and jammed with it heaps the last couple years and it's still running original tubes. I think the harp doesn't run them very hard really.
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HawkeyeKane
1011 posts
Jun 21, 2012
11:15 AM
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"But hey, sometimes I have forgotten to turn my 2x EL34 amp off for half a day, and I've gigged it and jammed with it heaps the last couple years and it's still running original tubes. I think the harp doesn't run them very hard really."
Yeah...I leave my 'Zoo on the entirety of a gig. And I think on one level you may be right about harp not wearing tubes out as quickly. But at the same time, I have to wonder why. Because some microphones can produce far more signal and feedback than guitar pickups can. It's weird how things like that work, isn't it?
I've been told by a couple different people that it's really not worth it to put a standby on my 'Zoo. But considering it still has its original JAN Raytheons, and considering that the NOS Raytheon 12AX7's now go for $200 per standard tested tube, and the fact that those tubes give me an absolutely golden sound that any current production tube probably couldn't compare to....I wanna preserve those babies as long as I can, so I'm either gonna start shutting her down on breaks or look into a standby for it.
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Hawkeye Kane
Last Edited by on Jun 21, 2012 11:16 AM
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Lmbrjak
103 posts
Jun 21, 2012
12:49 PM
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the principle involved is surge current. Cold circuitry and tubes allow for much higher current flow. As they warm up,resistance builds cutting down the current flow. Initial current can be many times the normal operating current but doesn't last long. I would assume standby keeps a small current flow going to avoid that surge but it's been forty years since I got a degree in radio tv service and 35 years since I've worked on anything.I do remember replacing tubes in televisions where people with weekend cottages turned their tv on before warming up the cottage.
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5F6H
1244 posts
Jun 21, 2012
2:12 PM
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@ Lmbrjak "the principle involved is surge current. Cold circuitry and tubes allow for much higher current flow. As they warm up,resistance builds cutting down the current flow."
Along the right lines but it's surge voltage...when an amp is cold the tubes draw no dc current from the power supply at all, because the heaters (filaments) aren't up to temperature. As the heaters warm the tubes, they begin to work & draw current, pulling dc voltages back down to normal operating range. An amp like a big Fender might draw an additional 100vdc before the heaters kick in. Not good for big power tubes, some tube rectifiers and power supply caps.
Preamp tubes warm up in the blink of an eye...no sweat there. Many smaller power tubes too...Hawkeye, your Zoo will last a decade on the same tubes. Champs Tweed Deluxes & Princetons, most SE EL84 amps never had standby switches.
Bigger tubes like 6L6s/EL34/6550 & KT90 are better off with a standby, especially with cold start rectifiers like SS or 5U4G (5AR4 and 5V4 have slow warm up, don't deliver any dc voltage for a good few seconds, by which time the heaters are often up to voltage and the tubes can draw dc current).
Standby is not a "mute" switch, as SuperBee says, if not playing for extended periods (over 20 min) you may as well turn the whole amp off. Cathode biased amps I would rather turn off between sets because the high idle currents are what creates most of the heat in a tube amp...they just get hotter & hotter the longer they are left on, in extreme circumstances they can burn out power transformer windings. Though it is quite normal for a cathode biased 6L6 amp to get so hot touching the chassis is uncomfortable..."hot" regarding human fingers is rarely "hot" as far as tubes & transformers are concerned (so please don't go touching things that you think may be hot).
Fixed bias amps run cooler idle and can often be left on almost indefinitely (certainly for an extended jam session), their bias method allows them to cool somewhat between heavy bouts of work. Of course, these are generalisations and amps are out there running non-optimal idle currents...if your amp smells unusually, or seems substantially hotter than similar amps, give it the benefit of the doubt & turn it off for a few minutes at a convenient point.
Either way, I don't recommend turning your amp to standby for long periods...they don't really like it. 6V6 & 6L6 amps with a standby just need around a minute tops between throwing power & standby. HK owners will testify that KT88 & KT90 need a few minutes, up to 5 or so? You only need to turn to standby for a few seconds before powering back down again.
@ Hawkeye - Yes harp mics kick out bigger voltages than most guitar pick ups (some humbuckers aren't far behind though), but often the bigger the signal you hit a tube with, the less proportionally, it amplifies (unfortunately battering preamp tubes with a big mic signal is where a lot of popular harp tone comes from). Plus amps EQ'd for harp can often cut back possible power outputs when compared to a guitar player with everything full up. So it's swings & roundabouts...because you can hit the amp with a bigger signal, it doesn't mean that you can capitalise on the power out.
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ElkRiverHarmonicas
1172 posts
Jun 21, 2012
2:28 PM
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I'll mostly defer to 5F6H, but I wanted to add:
People tend to think of tubes like light bulbs - you've got X number of hours, when you switch them on, that's harder on the filament - so where's the point that you should turn them off. But vacuum tubes are nothing at all like light bulbs, illustrated by the following anaglogy:
Incandescent light bulbs = Justin Bieber
Vacuum tubes = Chuck Norris
At my bedside is a Heathkit SB-310 International Broadcast Receiver. It has 9 vacuum tubes. Five of those tubes have been in that radio since 1969. Four of them I replaced last year ONLY because they tested weak. It's not in gingerly service either, I fall asleep listening to that radio every night.. thus it's on like eight hours a day every day.
Don't worry about it at all. Do whatever you want, leave it on, turn it off for the break. I don't think it matters.
I know, amps are not shortwave receivers, I'd say they're a lot closer to transmitters as far as tube action, but I'm just trying to say I don't think 10 minutes is going to make any difference whatsoever.
Just curious what's the plate voltage like on a amp at standby vs. running.
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David
____________________
At the time of his birth, it was widely accepted that no one man could play that much music so well or raise that much hell. He proved them all wrong.
R.I.P. H. Cecil Payne
Elk River Harmonicas
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Last Edited by on Jun 21, 2012 2:35 PM
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HawkeyeKane
1014 posts
Jun 21, 2012
2:56 PM
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"Incandescent light bulbs = Justin Bieber
Vacuum tubes = Chuck Norris"
LMAO!!!!
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Hawkeye Kane
Last Edited by on Jun 22, 2012 9:30 AM
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ElkRiverHarmonicas
1173 posts
Jun 21, 2012
8:01 PM
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;)
Probably ought to explain that a little better. With Chuck Norris and Justin Bieber, one is a mega-badass and the other is most definitely not, but they are the same in that they are both technically human beings.
Most high-power vacuum tubes are slightly radioactive. That's how badass they are.
The vaccuum tube started out life around 1900 as a suped-up light bulb. It was used like a diode to convert radio signals in the air - which are AC - to DC, which you could hear in your cool high-impedance headphones. In 1907, this dude Lee De Forest added another electrode and stuff and instead of just being a sort of diode, it actually amplified the signal slightly.
This undergraduate kid at Columbia, Edwin Howard Armstrong, figures out that hey, if we feed this signal back through the tube an assload of times, we can amplify stuff so you can actually hear it. That was the regenerative circuit - that technology could have made radio, television - everything possible, only he went off to World War I and came up with something better, the superhetrodyne circuit - which is what pretty much all radios and TVs use. Then he invented FM Radio in the 1930s... but an endless onslaught of B.S. from the player haters, namely De Forrest and RCA Kingpin David Sarnoff, drove him to jump out a window to his death.
But I'm rambling. Light bulbs are inherantly weak. Vacuum tubes are much more resiliant by design. In the high-power tubes, the tube filaments are still a lot like light-bulb filaments, except there is a little bit of Thorium in it. As an element, Thorium, is pretty badass. It's radioactive and there's nuclear power plants that actually run on it - it's pretty attractive for that, because its harder to make a weapon out of it and its a lot more common than uranium.
OK, so the vacuum tube works like this - when the filament gets hot, these electrons shoot off it - go through the vacuum and onto the plate. The cool thing tubewise about thorium is that it casts off these electrons at a much lower temperature, so to do the same job, it doesn't have to get nearly as hot. This is why your high-power tubes are more expensive, they've got Thorium in the filaments. Thorium ain't cheap.
They don't all have thorium in them, there's oxide coatings on the filaments, some that are tungsten, but they all do their job.
Spread the tube cost over that period of time. I just picked a common tube number out of my head - EL84 - a 9 watt tube I think, then checked what I could get it for online. $15. So, it's not that big a deal.
There was one radio station in Los Angeles that ran one tube for 10 years and got like 80,000 hours out of it, running thousands of watts through it. It still worked when they took it out and they keep it around for a spare. It was Thorium coated. Thorium is pretty awesome.
The most badass tube I ever saw was this vacuum tube at the museum of radio and technology in Huntington, WV. It sits in its own enclosure that's about seven feet tall. It came from a coal mining operation. the museum had an option of 50 of them and I asked the curator why they didn't get more of these awesome tubes. He says "Because it has 22 POUNDS of toxic mercury in it!"
Yes. Tubes are very badass.
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David
____________________
At the time of his birth, it was widely accepted that no one man could play that much music so well or raise that much hell. He proved them all wrong.
R.I.P. H. Cecil Payne
Elk River Harmonicas
Elk River Harmonicas on Facebook
Last Edited by on Jun 21, 2012 8:25 PM
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SuperBee
333 posts
Jun 21, 2012
9:37 PM
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@5F6H: Standby then, is only useful when powering up? I think that's what I should take away from the above. And I should always power up in standby mode with those amps where it is part of the design?
And my silverface Princeton reverb has had standby mod installed by previous owner. Standby of no value for this amp?
Thanks.
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5F6H
1245 posts
Jun 22, 2012
1:42 AM
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@ Elk River Harmonicas "Just curious what's the plate voltage like on a amp at standby vs. running." Typically the dc supply is interrupted in standby mode, so there is no plate, or screen voltage (fixed-bias amps will have negative grid voltage supplied to the pins). Grids can do funny things in this environment.
Guitar/musical instrument amps typically run tubes at voltages at well over data sheet recommendations at idle, add to that filter caps that might be seeing 100vdc+ over their rating (usually have a 50v or so surge capability) and power transformers that are not designed for continuous service applications and there is the potential for quite a difference between radio and musical instrument applications...whether that potential translates as a tangible effect is another matter ;-) As you say, leaving the amp on, unplayed for 10 mins is a non issue.
@ SuperBee - Standby's main advantage is at cold start, especially with SS & 5U4 rectifiers which deliver dc to the B+ rail almost instantaneously. GZ34/5AR4 & 5V4 have a slow warm up, which is nice for the power tubes, this lessens the impact of cold starts.
If your Princeton has a standby, then use it...it can't do any harm & makes life a little easier for the power tubes & filter caps. Repro manufacturers are tending to install standbys on amps that didn't have them in the 50's & 60's. Princetons that do eat tubes typically do so because of more immediate & significant reasons like screen voltages of over 130vdc beyond design max for a NOS 6V6! (EH 6V6 & JJ6V6 can take any voltage that a Princeton can throw at them, as can a properly biased amp with NOS 6V6, in general Princetons are not tube eating amps).
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SuperBee
334 posts
Jun 22, 2012
2:22 AM
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Thanks Mark. My '78 PR has 6v6 tubes which previous owner said were original, but all I know is they are Fender brand and the stencil says they are made in USA. He had also installed a bias adjustment pot and told me both extremes of the adjustment are within tolerance. Despite that advice I haven't been inclined to adjust it. It sounds great anyway! But I think it's probably safe to say its not too hard on tubes as it is
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Last Edited by on Jun 22, 2012 2:24 AM
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ElkRiverHarmonicas
1174 posts
Jun 22, 2012
4:42 AM
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5F6H... thanks for answering my question. I'm an acoustic player, so I'm basically playing into whatever vocal microphone somebody puts in front of me, so my knowledge of amps and such is pretty limited, my tube knowledge is all from radio. These tubes that amps take, what kind of filaments do they have typically?
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David
____________________
At the time of his birth, it was widely accepted that no one man could play that much music so well or raise that much hell. He proved them all wrong.
R.I.P. H. Cecil Payne
Elk River Harmonicas
Elk River Harmonicas on Facebook
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5F6H
1246 posts
Jun 22, 2012
5:49 AM
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If you're talking voltage requirements...6.3VAC at 0.3A (per tube) for most preamp tubes 0.45A for 6V6, 0.75A for EL84, 0.9A for 6L6, 1.5A for EL34/6550, 1.6A for KT88/KT90. Can either be centre tapped, or not depending on model.
Some amps run 12vdc heaters, more commonly in the preamp (in the old days these decisions were driven by what transformers the manufacturer could get cheap/surplus). Preamp tubes are designed as 12v, but usually wired 6v centre tapped, humbucking.
Materials-wise? I honestly don't have a clue...whatever the Russians, Chinese & Slovaks put in there?! ;-) Tubes are cheap (usually) disposable, plug in/out...if they don't work, or sound right, then I move on to the next brand. I buy them, but I don't make them, nor am I particularly interested in the intricacies of construction (every company has a USP/gimmick), because once you have a tube made a certain way, there's precious little you can to to change that tube, other than sub it out.
I have been taken in, in the past by conversations regarding the plating & alignment of grid wires, spiral filaments, getter style, how many spacers & what material...but really if there's no advantage at the speaker, or with longevity, it really doesn't count for much.
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HawkeyeKane
1015 posts
Jun 22, 2012
10:18 AM
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@ Dave
"I just picked a common tube number out of my head - EL84 - a 9 watt tube I think, then checked what I could get it for online. $15. So, it's not that big a deal."
That a single tube price? Most of the EL84's I've seen online are sold as matched pairs. $15 sounds about right for something like a pair of Sovtek 84's. I myself went for the JJ's for spares, but my band's bassist runs a Telefunken EL84 in his Marshall C5 and he has another one. I may stick that one in to see what it does to the 'Zoo tone.
@ Mark
Greg and I were discussing this yesterday but haven't come up with a definitive answer. Obviously, Raytheon has been a major Defense Department contractor since the days of WWII, and they made TONS of tubes for the military in the following years. Now, every true JAN Raytheon I've seen in the past has been stamped such as thus:
"MADE IN USA"
But recently I noticed mine are stamped with the Raytheon logo, the tube designation, and then "JAPAN".
So, I'm assuming mine probably aren't JAN after all. I don't think an American defense company would be manufacturing products in Japan during WWII...just a guess. I dunno how long Raytheon continued making tubes for the military after the war. Maybe they did make them out of a facility in Japan during the occupation? Either way, would you say these are most likely just military-grade tubes made for the civilian market?
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Hawkeye Kane
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5F6H
1247 posts
Jun 22, 2012
11:13 AM
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Raytheon stopped making vacuum tubes in the US in 1962, outsourced tube manufacturing to Japan. A couple of different companies, at least, made the Japanese Raytheons (Toshiba was one).
JAN designation doesn't correlate to any specific time period, could be anytime up to & inc. the 80's. Many military spec tubes carry a "W" suffix, e.g, "WGB", or "WA", "WB" (even the Sovtek tubes you get in new Fenders).
EL84s were all made after WWII (from 1953).
Tubes were often rebranded with another manufacturers names, you could probably go quite mad trying to ascertain provenance of every NOS tube! ;-) A certain brand, country of origin, or date does not guarantee great tone - some very desirable tubes were only made is some countries at certain times, under certain names, but that doesn't make everything by that manufacturer a great tube.
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HawkeyeKane
1016 posts
Jun 22, 2012
12:31 PM
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I'm not unhappy with my tubes by any stretch of the mind. They sound epic. I was just kinda used to the notion that they were JANs and liked that my amp was equipped with some of the highest quality tubes in history. Ah well......
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Hawkeye Kane
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ElkRiverHarmonicas
1179 posts
Jun 22, 2012
1:57 PM
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On the vacuum tube show and tell, which I enjoyed very much, I've got this one oddball tube. It's a 6AV11, the cross reference books dad has says it crossreferences with nothing. Dad has an electronics store tube tester display (which is one of the awesomest things ever)... it tested weak, but neither dad or I had a replacement. I haven't tried to get one on the internet yet, though.
As you know, somebody could detonate a nuke in the atmosphere and the vacuum tubes would be the only thing left running, but the writing is really fragile. Once, I picked up a tube and handled it while I tested it. I picked it up later and the writing was GONE! I have no clue what that tube is, lol. I've been far more careful since.
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David
I do have a serious question, Hawkeye. It looks like the amps are running current past what the tubes were designed to take... Did I understand that correctly?
Then why aren't we using appropriate tubes? Or probably more accurately expressed, why weren't those circuits designed with the appropriate tubes? I mean, they make tubes for 50,000 watt transmitters and stuff. There's no reason we couldn't have a tube that would handle that current easily.
____________________
At the time of his birth, it was widely accepted that no one man could play that much music so well or raise that much hell. He proved them all wrong.
R.I.P. H. Cecil Payne
Elk River Harmonicas
Elk River Harmonicas on Facebook
Last Edited by on Jun 22, 2012 2:05 PM
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5F6H
1248 posts
Jun 23, 2012
6:17 AM
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Hi David,
We don't run tubes beyond their current handling abilities, because if we did, the plates glow cherry red and then they die in short order :-)
Radio transmitters & the like are often designed, as you have mentioned, to be left running for days...longevity, long service intervals & reliability are key, the tubes might last decades. Guitar amp designers found that if they pushed up the plate voltages on the tubes, they got more clean power (and ahead of the competition) from those tubes...thus the guitar tone from the late 50's onwards, that is still venerated today, was born. Manufacturers weren't intending to build amps that lasted decades, they had new models coming out all the time that needed to be sold, they were principly concerned with not having to replace tubes within the warranty period. From the mid 50's to the eary 60's for instance, Fender biased their 6L6 amps progressively cooler, before nudging the plate current back up slightly for the BF amps in '63/64. In hindsight, since the end of the Wattage wars, amp manufacturers have the luxury of deciding on a point where they think a certain tube sounds best (& of course, ties in with available transformer requirements) and tend to run tubes at voltages that easily available & affordable tubes can tolerate, rather than 50-100v over rating like Fender & Traynor did in the late 50's/early 60's).
Voltage alone only kills certain tubes in certain designs where limits were pushed from inception. Normally tubes will run well in excess of data sheet (safe, ball park, recommendations) ratings if the plate current is kept within reasonable bounds. In more recent years manufacturers have released modern versions of tubes that far exceed NOS in terms of voltage handling ability, even though rated dissipation hasn't changed significantly (you run them at more volts, less current).
You could build a guitar amp to run the tubes as long & as reliably as a radio transmitter easily...it just wouldn't sound like an amp that people would want to buy. Tubes that take more current & voltage are being developed all the time (KT90, KT120) but they are expensive (manufacturers don't like that), don't sound like more commonly used tubes (players don't like that) and require bigger, heavier, more expensive power transfomers with massive filament windings (no one likes that), and you typically get stuck with one brand & supplier.
Your "50,000W radio transmitter" is designed to run at 50,000W safely & for a long time...if it were a guitar amp it would make 75,000W, tubes might need changing every 2-5yrs and you would have to build the venue around the amp ;-)
Your 6AV11 is a triple triode, the internals are the same as for certain 12A#7/6S#7 style, medium mu twin triode tubes. Nowadays, if designing a similar circuit, it would be cheaper & easier to use 2x noval sockets & 2x twin triodes (either paralelling 2 triodes, or leaving a triode disconnected), rather than source compactron tubes & sockets.
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Last Edited by on Jun 23, 2012 6:23 AM
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