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Post subject: Re: Fender Blues Junior
Posted: Mon Dec 18, 2017 7:27 pm
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strayedstrater wrote:
Just following the instruction manual is really all you need to do.

Tubes are a little less reliable than transistors. Sometimes tubes fail suddenly for no apparent reason. And they have a variety of failure modes, from getting hissy to not working at all.

But tubes are a lot more rugged and reliable than a lot of people think. Car radios used to have tubes. Fighter planes, jet airliners, missiles and rockets used to have tubes. (Some in-service fighter planes still do.)

Bands truck tube amps all across the country, play cranked shows, then toss them back in the truck.

Some people say you should let a freezing cold amp warm up to room temp before turning it on. Others say that after playing you should let the tubes cool for a few minutes before moving the amp. Some people say the longer you let the tubes warm up in standby the better.

None of that can hurt, but none of it is super critical either.

Turning a tube amp on-off-on-off-on-off a bunch of times really fast is hard on the power supply. Don't let your kid do that.

Otherwise, just read and understand the manual, then play it and enjoy it.

The least reliable amp I ever had was solid state. Most of my tube amps gave me many years of service with zero problems.


Usually, when I use my tube amp, I play it for a half hour or more, then I turn it off for the day or use it later. So it's not overly used for crazy amounts of time or anything.


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Post subject: Re: Fender Blues Junior
Posted: Mon Dec 18, 2017 8:46 pm
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You could play it 24 hours a day 7 days a week for years -- you'd die doing that long before the amp died.

Some tube hifi people never turn off their amps and preamps. They believe their gear sounds best when the heat has fully equalized and stabilized.

Obviously if a tube has an 8,000 to 10,000 hour lifespan, the more you play the more hours you use up. But 40 hours a week is 2,080 hours. Roughly 4 years before you'll need to replace tubes.


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Post subject: Re: Fender Blues Junior
Posted: Tue Dec 19, 2017 6:19 am
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strayedstrater wrote:
... Some tube hifi people never turn off their amps and preamps. They believe their gear sounds best when the heat has fully equalized and stabilized...


Good point, and I believe that it is the heating/cooling cycles that are harmful to any electrical device, as in on/off cycles. I often leave an amp on for long periods of time, then pick up the guitar and play whenever the mood strikes. I use the standby in between playing.

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Post subject: Re: Fender Blues Junior
Posted: Tue Dec 19, 2017 12:16 pm
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shimmilou wrote:
strayedstrater wrote:
... Some tube hifi people never turn off their amps and preamps. They believe their gear sounds best when the heat has fully equalized and stabilized...


Good point, and I believe that it is the heating/cooling cycles that are harmful to any electrical device, as in on/off cycles. I often leave an amp on for long periods of time, then pick up the guitar and play whenever the mood strikes. I use the standby in between playing.


Well, unfortunately, the Blues Junior doesn't have a stand mode switch.


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Post subject: Re: Fender Blues Junior
Posted: Wed Dec 20, 2017 3:50 am
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Mine does! :D

But, if no standby, no big deal, just leave it on if you think you might want to return and play later.

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Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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Post subject: Re: Fender Blues Junior
Posted: Wed Dec 20, 2017 7:13 am
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shimmilou wrote:
Mine does! :D

But, if no standby, no big deal, just leave it on if you think you might want to return and play later.


And that's ok for it to do? That won't hurt the amp? The way I have my set up is, my amp and One Spot, which powers all my pedals, are on the same surge protector so if I left the amp on, I'd have to unplug the pedals when their not in use.


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Post subject: Re: Fender Blues Junior
Posted: Wed Dec 20, 2017 7:49 am
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In trying to calm your concerns I seem to be creating new anxieties.

You said you were being careful not to play your amp for long periods.

My response was meant to reassure you that you can play it as long as you want, as much as you want, as often as you want.

The audiophile example of leaving tubes on all the time was the extreme case to show that tubes can handle pretty much whatever you do to them.

The heaters use dozens of watts. Some amps do sound a little better when they've been on for hours, but it's a bit of a waste of electricity to leave it on when not playing.

Perhaps you misunderstood my earlier passing comment about turning the amp off and on a bunch of times very quickly. I meant throwing the switch click click click click click click click click -- the sort of thing a small child might do, or someone who's really stoned or drunk might do.

You can turn your amp on, play for a while, then turn it off as often as you want. Just don't turn it off and then instantly turn it back on. Give the magnetic fields in the transformers a second or so to fully collapse before re-energizing them.

(And don't obsess about that. If your house power flickers off for a moment and then comes back on while you're playing, don't worry. There's like a 0.000001% chance of damage. Again, a kid playing with the power switch was an extreme example of something that might possibly sometimes be bad.)


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Post subject: Re: Fender Blues Junior
Posted: Wed Dec 20, 2017 8:23 am
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And Shimmilou's comment about thermal cycling (heating up then cooling down) being the hardest part of an amp's life?

Keep in mind that's true for everything. Your TV, your computer, lightbulbs, your car, your oven, your microwave. Things expand when they get hot and shrink when they cool off. Some parts get hot and expand first, then the heat spreads out and other parts start to expand. So you get waves of microscopic physical deformations and stresses. And then the reverse when you turn the device off. It's not a "tube amp thing" and you don't need to worry about it anymore than you do when you turn on your TV.

Tom Morello has been playing the same Marshall JCM800 since the beginning of Rage Against The Machine. Thousands of shows, millions of miles in trucks and planes, countless hours in the studio.

It's never broken down. Still has the factory stock tubes. His tech has never even removed the back panel to check anything. They just plug it in, turn it on, and he plays.

That's another extreme example. Don't expect to get 25 years of flawless performance from your amp without any maintenance. But it's possible.


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Post subject: Re: Fender Blues Junior
Posted: Fri Jan 05, 2018 4:57 am
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Hi all,

I found this thread and decided to post my question here. Hope this is right.

Guys, it is not clear to me whether after a tube swap, biasing is needed ??

Did anyone here change tubes on a blues junior III?
Thanks all,
Dam


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Post subject: Re: Fender Blues Junior
Posted: Fri Jan 05, 2018 6:28 am
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Jokers_Wild wrote:
Hi all,

I found this thread and decided to post my question here. Hope this is right.

Guys, it is not clear to me whether after a tube swap, biasing is needed ??

Did anyone here change tubes on a blues junior III?
Thanks all,
Dam


It would have been better to start a new thread since biasing is a different topic. A new thread with a title like "does the Blues Junior III need to be biased" will attract new viewers and more answers.

There are two common amp bias designs. One is "cathode bias", which self adjusts to some degree. It can change the bias voltage itself. But it sounds a bit different, and it produces less output power.

The BJrIII is not cathode bias.

The other design is "fixed bias". The bias voltage is preset to a certain voltage (a "fixed voltage"). That voltage will drive some tubes too hot, other tubes too cold, and be just right for other tubes. These amps should have the bias checked and adjusted when changing power tubes.

The BJrIII is fixed bias.

Some fixed bias amps have a trim pot that makes it easy to adjust the bias voltage. Others use resistors to set the bias voltage -- to change the bias you need to change the resistor (or replace the resistor with a trim pot).

The BJrIII has a bias resistor, not a bias pot.

If your power tubes have bias markings on them, you can buy the same brand of tubes with the same markings and plug them in without biasing.

With other power tubes, ideally you should check the bias and adjust if needed. But if your amp is still under warranty, you'll void the warranty by changing the resistor or replacing it with a trim pot. (If a Fender Authorized tech changes the resistor that should maintain the warranty, but be sure to keep the receipt.)

Unlike most Fenders, the Blues Jrs come from the factory with the bias set hot. That's pretty common with EL84 amps. While Vox AC15 & 30 are cathode bias they're designed to run hot bias and push the tubes very hard. Same for the Orange Tiny Terror.

The result is shortened tube life. Many people also say the BJr and OTT sound better with the bias altered to not push the tubes so hard.

Just about all EL84's will function safely in a BJrIII without checking and adjusting the bias. As long as the big metal plates don't glow orange or red, they're safe for your amp. They might not sound as good as they could, and they might not last as long as they could, but they won't hurt your amp.

However, if your amp develops a problem it's conceivable that they could weasel out of a warranty repair by claiming you caused the problem by replacing the tubes incorrectly. So keep the old stock tubes and put them back in before taking your amp in for repair.

Oh, since I've seen people ask this question -- preamp tubes don't need bias adjustments, only power tubes.

Preemptive edit: when I say "hot bias" I mean high plate dissipation.


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Post subject: Re: Fender Blues Junior
Posted: Wed Jan 10, 2018 3:42 am
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@strayedstrater

Thanks a lot for the detailed information. This is Gold. Could not find these info somewhere else so detailed and in one place.
Understood!

Beer is on me!
Cheers,
Dan


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