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Post subject: What do you guys think of these tubes for blues jr?
Posted: Thu May 26, 2011 9:47 pm
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http://www.torresengineering.com/bfobljrfe.html

Heard some good things about them, curious of what y'all think. Will I have to do anything with the bias of my amp if I switch to these (I'm clueless when it comes to that stuff, so I'd rather not).


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Post subject: Re: What do you guys think of these tubes for blues jr?
Posted: Thu May 26, 2011 11:24 pm
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Hi Lucryster,

I am not a fan of JJ tubes, I just haven't used many of them, I prefer GTs, but that's just my opinion, there are JJ fans here too. There are considerations any time that you change output tubes, and also considerations for the BJr concerning output tube biasing. The following quotes sum up my thoughts on the BJr and biasing. :)

"Obviously, there are a lot of BJrs out there cranking away at 11+ watts idle dissipation. They're not bursting into flames or melting their vinyl covering or anything. But they'll last longer and sound better if they run a bit cooler. I've seen many older stock Blues Juniors with heat damage to the circuit board that holds the tubes, and the expansion and contraction caused by the high heat causes solder joints to crack."
http://home.comcast.net/~machrone/bjr/bjbias.htm

"Do I really need to bias my amplifier every time I change tubes?

You will occasionally hear guitarists say things like "In the old days, we just bought new tubes, stuck 'em in, and started playing", and "We didn't worry about biasing back then, and you don't need to now", or perhaps: "Biasing is a myth". In most cases, you don't have to bias your tubes when you change them. You can just plug a new set in and start playing, especially if you aren't too particular about setting up the amp for the absolute best tone. However, if the new tubes you have plugged in are different enough from the ones that were in there, with respect to current draw for a particular grid voltage, they may end up biased too hot for that particular amplifier. In this case, your new tubes will start to glow cherry red on the plates, either at idle or while playing, and they will soon be destroyed. In addition, the tube may short out and take out the output transformer in the process, leading to costly repairs. Tubes of the same type from different manufacturers will usually vary greatly in current draw at a particularly grid voltage, but even two different tubes of the same type from the same manufacturer can vary widely in their current draw. For these reasons, it is always best to check the bias after installing a set of tubes. If you are in an emergency situation, such as a blown tube in the middle of a gig, you can go ahead and stick in your spare tubes, but you should turn the amplifier on and look at the plates of the tubes (the large dark grey metal element) in the dark, both at idle and while playing, just to make sure they aren't glowing red. Often, when a tube fails, it will take out the screen grid resistor, and any new tube you plug in will glow red, or won't work at all. In this case, you have no choice but to repair the amplifier before using it."
http://www.aikenamps.com/Biasing.html

"Before you do another thing with your Blues Junior, get the bias under control! The way it came from Fender, it's running the output tubes way too hot.

Bias is a negative voltage that's applied to the grid of the tube that controls the amount of electrons--the plate current--that hit the plate. If too many hit it, the plate overheats. It can actually turn red and even melt. But long before the plates melt, excessive plate current shortens tube life, overheats your output transformer, and makes your amp sound bad. The maximum rated plate dissipation for an EL84 is 12W, so for class AB (the way the tubes interact with the output transformer) operation, it should dissipate approximately 70 percent of that, or 8.4W, at idle. The stock Blues Junior dissipates nearly 12W per tube at idle, meaning that as soon as you turn the volume up, you're exceeding the tube's design limits. I have no idea why Fender chose to set the amp up this way--they certainly know as much about tube circuits and operating parameters as anyone. If you fix their error, however, your amp will sound better and last longer. I've measured the temperature difference between a the output tubes of a stock-biased Blues Junior and one that's properly adjusted, and the difference can be as great as 100°F."
http://home.comcast.net/~machrone/bjr/bjbias.htm

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Post subject: Re: What do you guys think of these tubes for blues jr?
Posted: Fri May 27, 2011 5:04 am
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I use JJ alternatively Sovteck (both EL84 and 12ax7) on my Vox. My experience on the Vox is that JJ are sweet but Sovteck are more clean, but that a different circuit than the BJ.

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Post subject: Re: What do you guys think of these tubes for blues jr?
Posted: Fri May 27, 2011 5:11 am
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JJ's here too. Great sounding and durable current production tube. GT's do nothing for me. Fender owns GT that's why they're in their amps. But I'm not going to get into a tube debate. Try out some different manufacturers and see what you like. The bias needs to be checked whenever you change power tubes for best performance and tube life. You don't have to worry as much with a cathode biased amp. I still check it anyway. Components drift with age and use.

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Post subject: Re: What do you guys think of these tubes for blues jr?
Posted: Fri May 27, 2011 8:02 am
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Cool, I knew that there were some JJ fans here. 8) To be clear, the BJr is not Cathode biased. :idea:

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Post subject: Re: What do you guys think of these tubes for blues jr?
Posted: Fri May 27, 2011 8:07 am
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Nope, It's fixed bias and needs to be checked. The Blues Jr's are usually biased pretty hot which is why they sound the way they sound but also eat up tubes. Of the newer amps I believe the Vibro Champ and Tweed Champ are cathode biased.

Thanks Shimm, I should have made that more clear.

If you're looking at JJ's look at www.eurotubes.com great prices and service.
I never liked Torres and I have my reasons that I will not discuss here. :x

Here's the link to the Blues Jr.
https://ssl.eurotubes.com/cart/index.ph ... gory_id=31

You don't need gold pin tubes. They're just a waste of money. :wink:

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