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Post subject: Blues Junior output tube s
Posted: Sun May 12, 2019 8:30 am
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Hi to all,
I’m hoping I can get some opinions about my new amp on power tubes. I just purchased a used 2015 tweed Fender Blues Junior. I always wanted to get back to a tube amp after a 35 year hiatus.

It’s in very good condition and seems to be working fine but I thinking about picking up a backup set of power tubes. Right now the amp has the original Groove Tubes that are marked as 4. According to the fender website the number 4 is on the low end of the medium scale.

MEDIUM 4-7 Normal performance, great dynamic range/attack and best all-around rating type for all styles of playing.

On reading up about the amp it appears that it does not have adjustable bias and is set hot from the factory and tends to eat power tubes.

I understand that a mod for adjustable bias for this amp is available but I do not have the knowledge that I feel is needed to install or someone locally to do this.

For reference I try to nhave the amp set for a very clean sound without a lot of grit. The master volume is usually set at around 6 and the regular volume between 2-3 using a Gibson SG with a single coil.

I have heard very good things about the JJ tubes but they do not have a rating from what I have found.
Has anyone done a direct replacement of the JJ power tubes into this amp without having a bias mod on the amp with good results? Like I mentioned I ‘m not planning on driving the amp hard and just want the best reliability. Also it’s only used a couple of hours a week not every day. Any suggestions on other types of tubes that would accomplish this would also be welcome
Thanks in advance
dad roadie


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Post subject: Re: Blues Junior output tube s
Posted: Sun May 12, 2019 9:02 am
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The Groove tubes marked EL84-S are JJ manufacture. The S stands for Slovakia, country of origin. So if you buy the GT #4 again, you will get JJ.
But just because JJ makes the tube, that doesn't mean its the same unit as the GT.
Much of the cost and difference in the manufacture of tubes is the carbon coatings that make the tube innards black. there are different grades of coatings and just because its made by the same company doesn't guarantee the same quality of coatings. These coatings are what the electrons hit after being boiled off the cathode. The electrons are absorbed and contribute to the music or they bounce off leaving only a "Tic", which causes noise. The factories only need ,"good enough".
Picker are always on the hunt for low noise tubes. Most of the good ones are old. This is fine for preamp tubes, but don't try to stick NOS tubes in the power stage of a BJr unless you can build an adjustable bias for them.
On their preamp tubes, JJ makes three grades, a low microphonic tube with no coating, a red label with dark coatings and a gold label with a light coat. There is no apparent difference in the power tubes, but if you want to try JJ EL84s, you need to spec three grades, low, medium, or high bias tubes when you order by phone to Antique Electronics. Other providers may be able to do the same.
The red labels on power tubes burn off when they run too hot of a bias. You can guage the age, condition and bias by the label condition.


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Post subject: Re: Blues Junior output tube s
Posted: Sun May 12, 2019 10:22 am
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Hi Tim,
Thanks for the reply,
I'm a little confused as far as if the JJ power tubes are ok to use. Sorry I'm an old guy.

As a note the current Groove Tubes in the amp have a very clean red number area with no burning of the paint showing so I figure from what you said they are running ok .
Should I stay with the Groove Tubes possibly going up a number (to 5) to help it run a little cleaner ? Or do I need to stay with the 4s

I do buy from Antique Radio Supply all the time. If I use the JJ EL84s, which grade , low, medium, or high bias tubes would you go with so that I would not have an issue with the bias and still maintain the cleanist sound possible and a good reliability. ?
Thanks again .Sorry for my confusion.
Regards
dad roadie


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Post subject: Re: Blues Junior output tube s
Posted: Sun May 12, 2019 6:55 pm
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Low bias tubes are what you get for a BJr. AES has low bias JJ or GTs. Go with the same number.


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Post subject: Re: Blues Junior output tube s
Posted: Mon May 13, 2019 6:40 am
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Thanks again Tim'
I'll go ahead and order a set of Groove Tubes with the same number (4) and take it from there.

Has anyone with a MIM Blues Junior, (creme board) had decent tube life on the power tubes without doing the bias mod by staying with the same rating on the tubes?

Like I mentioned I do not feel I have the ability to do this or the funds to have it done. I can solder well and have a good DMM but I have heard that its a difficult mod to install due to removing the board from the amp and the ribbon cables and such. Being an old guy my hands and eye sight are not what they use to be.

The amp is working well at the moment and I'm under the old saying "if it ain't broke don't fix it"
But if it's a time bomb waiting to happen I want to avoid that situation.
Thanks again for all the help and suggestions!
dad roadie


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Post subject: Re: Blues Junior output tube s
Posted: Mon May 13, 2019 7:41 am
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dad roadie wrote:
The amp is working well at the moment and I'm under the old saying "if it ain't broke don't fix it"

Here is a new saying: "if it ain't well designed, don't buy it". :lol:


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Post subject: Re: Blues Junior output tube s
Posted: Mon May 13, 2019 9:55 am
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ghost_of_strings wrote:
Here is a new saying: "if it ain't well designed, don't buy it".

And let us not neglect Confucius......

If the quality is long remembered, the price is soon forgotten.

:wink:
Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Blues Junior output tube s
Posted: Mon May 13, 2019 10:25 am
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Two more cents, if the amp is operating fine w/ 4's you could probably go with 3's or 5's without incident.
3's would breakup earlier and the 5's would give slightly more clean headroom.
It is still prudent to check the bias of output tubes to ensure they are operating optimally in your amp.


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Post subject: Re: Blues Junior output tube s
Posted: Mon May 13, 2019 10:31 am
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Unfortunately, every tube is a time bomb. Some with shorter fuses than others. Tubes have a Constitutional right to fail any time. That's why gigging musicians always have a backup, tubes or amp.
Like I've said in other posts, playing your amp is the worst way to treat it. Vibration kills tubes. It happens like a stroke. OK one minute, dead the next. You hear a loud hum for a sec, then a loss of volume, maybe a crackle before the fuse blows. Then you feel as let down as Elon Musk when they shook his Dragon twice as hard as it was designed for. They hadn't even fired the engines yet before it came apart. Too bad he couldn't plug in a new set of tubes.


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