Tube Amp Myths

For fun, or in all seriousness, let's see what's out there.

Here's mine: You don't need to wear a hazmat suit to pull tubes. Nor any kind of gloves to protect the tubes from 'skin-oil'. Washing hands is enough, and is even likely unnecessary, unless you just finished a 'meat-lover's slice' or were working o a greasy engine.
 
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efstop

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I bought a JHS Little Black Amp Box. It's a volume control you use in the effects loop. I tried it with my Mini Jubilee and it works as advertised. I could have built one for a lot less, but I'm lazy and I suck at soldering. Cheaper than a volume pedal, too.
 

charlie chitlins

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Attenuation tech is starting to deal with this. The 'Headroom/Bedroom' power scaling feature on my Orange makes for some excellent bedroom toanz.
There's still no substitute for a pushed speaker.
The whole bedroom tone thing totally baffles me.
There are pedals made to emulate a pushed amp and speaker.
You can never push a speaker at low volume...emulating this sound is the best bet.
The best "bedroom" tones I've heard were from pedals/modeling.
 

ehb

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A speaker needs enough juice to do what it does....Gotta get up into the curves...
A bass cab needs enough juice to reach a pressure level to sound right....


That being said, it doesn't have to be a huge amount for a guitar speaker nor massively loud...


Some folks like the sound of the speaker getting weird or breaking up (I just call it flutter). I don't.

I am of the opinion that optimum is the speaker reproducing what is sent to it from the amp section as accurately as possible. If I were regularly gigging guitar again, I would be playing through older higher power JBL, Cetec Gauss, or EVMs that can handle what is thrown at em without coloring much at all...

An old band mate's 4x12 was actually on old "deep" Traynor 4x12 loaded with those heavy badass Gauss 12"s.... I had a Marshall too with a 4x12.... His rig sounded amazing...better than mine with C spkrs... I just didn't like rolling his up the truck ramp....like pushing a damn Buick Electra duece and a qtr....
 

charlie chitlins

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For fun, or in all seriousness, let's see what's out there.

Here's mine: You don't need to wear a hazmat suit to pull tubes. Nor any kind of gloves to protect the tubes from 'skin-oil'. Washing hands is enough, and is even likely unnecessary, unless you just finished a 'meat-lover's slice' or were working o a greasy engine.
I assume the skin oil thing comes from halogen light bulbs, like automotive headlights.
In that case, it's true.
 

ChiefTenthunbs.

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I bought a Blues Junior 3 probably 3 years ago, and after a while it just didn't sound quite right. I stopped playing it and instead used an old Marshall solid state amp i have.

I took it into my local guitar shop, and they were about to buy it from me but after extensive testing in store they decided it wasn't right and needed a service. The aged rocker type that worked there gave me a lecture about how tube amps don't like being played at bedroom volumes and they need to be cranked up or they start to play up. So . . is there any truth to that? I took it out once for the one and only time i ever took it to a bar with my guitar teacher and i think it toppled over in my boot . . i would think that's probably the root of the issues. When i turn it on now it has got worse and one of the tubes glows pink and that's about it . . so i know it needs a few new tubes at least.

Was he talking rubbish then?
I’m sure it doesn’t hurt to to crank it up but in my experience, playing a tube amp at low volume wont hurt anything. I used to play cranked up pretty loud when I was a pup but I learned neighbors don’t like rock bands in the apartment building. So I started playing at a very low volume. None of my amps have ever balked or had any trouble of any kind. And I’ve been playing at low volumes most of my life and I’m 60, and I’ve been playing since I was 12 or 13 so to that I call b.s.
As far as your amps tube glowing pink, yeah, pull them and test them and replace any and all bad tubes. If you change the tubes, if you turn it on and it doesn’t immediately act like the old amp before the fall, you’re done. Turn it off and have it repaired.
 

Scott A Novak

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Do amp tubes need to be changed periodically (like oil changes on a car), or do we just go with them until they fail?
Can changing tubes to a different brand make one sound better?
RE: Tube Life & Tone

Tubes can last a very long time IF a number of conditions are met.

Tubes must run at the proper filament voltage. Unfortunately many vintage tube amps were designed to run on 110VAC, 115VAC and 117 VAC. While they will still run on today's 120VAC nominal line voltage, the increased filament voltage will cause the tubes to wear out FASTER and FAIL faster.

There are some designers that promote using a filament voltage slightly lower than the rated filament voltage. While a tube running at the rated filament voltage will have a higher transconductance than a tube running with a lower than rated filament voltage, after a few thousand hours of use, the transconductance of a tube running at the rated or higher filament voltage will be LOWER than the tube running at a lower than rated filament voltage. Essentially, if you design the circuit around a lower transconductance and run the tube at a lightly less than rated filament voltage, you can get 10,000 hours or more of life from the tube, at least for the small signal tubes.

With output tubes you don't want to run at much less than the rated filament voltage.

If you have a vintage amp what can you do? The easiest solution is to add small value resistors in series with the filament voltage supply and adjust the resistor values until the filament voltage at the tubes is reasonable.

The bias current on the tubes must also be reasonable. Note that the bias current of output tubes is not always reasonable from the factory, even in so called "self biasing" circuits. A competent electronic technician can adjust the tube's bias current so that the tubes will run reliably for a long time. The tube's bias voltage is irrelevant. It's the correct bias current that you need to achieve in a given circuit.

The tubes must also be run conservatively at reasonable plate dissipations and plate voltages, even when driven into severe clipping, otherwise the tubes will wear out and/or fail prematurely. Some amplifiers were designed using excessive plate voltage and will only work reliably with a brand of tube that is significantly BETTER than the specifications for that tube number.

While different brands of tubes can sound different, often the biggest difference in sound is caused by incorrect bias current. 12AX7s vary so drastically in their characteristics from one brand to the next that they should really be divided into about 5 different tube numbers. A Telefunken smooth plate 12AX7 may sound great in an amplifier that was biased for it, but it may sound terrible in an amplifier that was biased for a different brand of 12AX7.

You can't draw a correct conclusion about the sound of a particular tube UNLESS you know that the tube has been biased correctly. Add to that, some guitarists want a particular type of distortion and are basically selecting tubes to turn their amplifier into a distortion generator.

Tubes with a higher internal vacuum perform better than a tube with a lessor vacuum. This is especially noticeable with output tubes. The higher the vacuum, the less blue glow you will see, the better that the tube will perform.

I'd recommend testing all tubes with a transconductance type tester and if the tube measures well, continue to use it.

Scott Novak
 
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Dolebludger

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Scott,

After I spend four years at MIT getting a degree in electrical engineering, I'll read your post again. Maybe then I'll be able to understand it!.
 

CB91710

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The bias current on the tubes must also be reasonable. Note that the bias current of output tubes is not always reasonable from the factory, even in so called "self biasing" circuits. A competent electronic technician can adjust the tube's bias current so that the tubes will run reliably for a long time. The tube's bias voltage is irrelevant. It's the correct bias current that you need to achieve in a given circuit.
Th Blues Jr in particular is generally biased quite "hot" from the factory, and red-plating after tube replacement is not uncommon.
 

bilbarstow

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@Dolebludger - I'm not @Soul Tramp - but I can give you the simpler version.

Tubes have "proper, expected" voltages and Bias values. Individual tubes have variable response to approaching / diverging from those nominal values. People can make adjustments to the values that the tubes "see" and this allows some optimization / customization of the amps sound and performance.

For most of us, it requires a Tech to make the adjustments / changes required for this level of "tuning".
 

Big John

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This thread started out with myths, cracks, and jokes...and then went 180 with all this seriously serious seriousness. Hey, the socks don't have to match all the time.
 

cybermgk

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For fun, or in all seriousness, let's see what's out there.

Here's mine: You don't need to wear a hazmat suit to pull tubes. Nor any kind of gloves to protect the tubes from 'skin-oil'. Washing hands is enough, and is even likely unnecessary, unless you just finished a 'meat-lover's slice' or were working o a greasy engine.
You should never pull tubes by grabbing the glass anuhow, always pull, grabbing the base.
 

cybermgk

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Two biggest myths are that you need matched sets of power tubes and balanced PI tubes.
Need? no. BUt most amps have a single bias pot. If the O tubes are mismatched, you'll never have the amp biased properly for all tubes.
 




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