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Post subject: Fender Blues Junior III Replacing Tubes
Posted: Mon Apr 03, 2017 2:59 pm
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Hi Everybody !
I'm New to American amplifiers.
I have a Marshall jcm2000 tsl601 , and im gonna sell this amp then get a Fender Blues Junior III
But i know that its not completely clean , i cant remember exactly but i think it starts to crank up from volume set to 7 ...
So i wanted to know if there is any suitable tube to replace the stock ones to GET ONLY CLEAN TONES FROM THIS LITTLE AMP ?!


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Post subject: Re: Fender Blues Junior III Replacing Tubes
Posted: Thu Apr 06, 2017 12:49 am
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No, you will not get "only clean" with a tube swap. The amp is designed to be clean or get some grit depending on how the master and volume are set. You can get good clean with the master cranked and the volume low,or vice-versa for grit. So, the clean begins to get gritty as the volume is increased.

There are mods that you can do to get more clean, but they require substantial changes to the amp, such as changing major components to accomodate 6L6 tubes.

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Post subject: Re: Fender Blues Junior III Replacing Tubes
Posted: Thu Apr 06, 2017 1:55 am
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First;
You can put 12AY7 on V1 you'll have more clean and with less output power.
5751 tube in V1 give more power and less clean than 12AY7.

All original tubes in this amp are 12AX7 with 100 % gain
5751 = 70%
12AY7 =45 %

Second ;

You also can replace all other 12AX7 with these tubes too.

All these mods are safe for the amp .


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Post subject: Re: Fender Blues Junior III Replacing Tubes
Posted: Tue Feb 27, 2018 7:45 am
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Hi guys, I would like to ask about the output tubes. What are the best for clean sound? As I saw on the Groove tubes catalog that there are no Hard (8-10) EL84 . Just “medium” power range, so I have no choice just medium 4-7. But there are two different on their catalog GT-EL84-S and GT-EL84-R. Also if I can use 12AY7 on V1, V2 and V3 for cleaner sound I can use and 12AT7 for even cleaner sound without any issue. Right?

Thank you


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Post subject: Re: Fender Blues Junior III Replacing Tubes
Posted: Sun Mar 04, 2018 2:11 am
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The "S" version is made by JJ (Slovakian), and the "R" version is Russian (EH or Sovtek). The S would probably be a bit cleaner than the R, but depends on the grade of either (hard or soft, harder=cleaner).

The only good spot for a 12AT7 is the V3 (PI) position, IMO. A 12AT7 in the V3 position would help for cleaner sound. Generally speaking, a 12AT7 in V1 and/or V2 will not give a good sound. A good compromise would be a 5751 (or 12AY7) in V1, a 5751 in V2, and a 12AT7 in V3, which will give you a good clean sound, without loosing as much tone as with having even lower gain tubes in V1 and V2. Part of the function of the preamp tubes is tone stack recovery, and too many low gain tubes would cut the signal too much, leaving a sterile tone.

The lower gain tubes are good for a better clean sound, but at the expense of output/volume. You can already get great cleans at lower volume, keeping the Volume pot low and using the Master pot for volume.

With the stock BJr amp having a very hot bias, the amp is designed to get more grit as the volume is raised.

In any event, changing the preamp tubes to any compatible tube (12AX7, 12AT7, 12AY7, 12AU7, 5751) will not harm the amp at all. But, when changing output tubes, a bias check/set is prudent. So, try different preamp tubes and see what you like.

The BJr does not have a bias adjust pot, but adding one, or changing the bias resistor, to adjust for a cooler bias would also help get better clean tone.

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---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

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


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Post subject: Re: Fender Blues Junior III Replacing Tubes
Posted: Sun Mar 04, 2018 6:23 am
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A 15 watt amp will not, can not give cleans that are as loud as a 60 watt amp.

Lowering the gain of the preamp tubes will not, can not give you significantly louder cleans. You can turn the preamp and master knobs up higher, but the signal going to the power tubes will be lower. As soon as you turn the preamp and master high enough to get 15 watts out of the power tubes, they will begin to distort.

If you want louder cleans than what the Blues Junior can do, you need a bigger Fender amp.


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Post subject: Re: Fender Blues Junior III Replacing Tubes
Posted: Tue Mar 06, 2018 5:16 am
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Thank you very much for your answers guys. Yeah I know I can never have the super reverb clean but at at least if I set my amp not loud I suppose I can have a bit clean sound. The groove tubes site writes for clean sound I need high (8-10) EL84 I have the same in my super reverb (I mean 8-10) and I like more compering the (1-4) or (5-7). The problem is its very hard to find them, at least in UK. Even in USA I saw just a few stores have the high range (8-10). If anyone knows any store with 8-10 in UK or Europe please let me know. Thank you


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Post subject: Re: Fender Blues Junior III Replacing Tubes
Posted: Tue Mar 06, 2018 1:51 pm
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I think the ratings of tubes (1-4), (5-7), (8-10) have to do with the tubes conduction ability given the same bias voltage. They use to be color coated, Red,White, and Blue. So figure out which is which. I can't tell you because I can't think that well. I'm guessing a colder bias will provide more headroom?

But then again, i've read distortion is created in the pre-amp section, as mentioned above with switching preamp tubes to lower the gain. The George Benson HRD uses a 12AT7 for V1, apparently to provide a clean signal through the preamp section of the amp. Low distortion.

Also the George Benson HRD uses a high wattage speaker 100W, to avoid any speaker break-up, as I've read. So perhaps upgrading the speaker will give you a sense of a cleaner sound.

I bet you'll be happy with a Blues Junior and be surprised that you can get a good clean tone as simmilou has suggested using the vol and master controls to provide that. The Blues Junior is another great Fender amp, I own one. Maybe you can tell I'm also interested in a George Benson HRD.


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Post subject: Re: Fender Blues Junior III Replacing Tubes
Posted: Tue Mar 06, 2018 10:34 pm
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When a tube is driven to saturation (100% conduction), the wave will flat-top and distort. This can happen in any gain stage in the preamp OR on the power tubes.
Master on 4 and Volume on 11, that's all preamp distortion.
Master on 11 and Volume on 4, that's likely all from the power tubes.
Master on 11 and Volume on 11, you're getting everything including the speaker.

Cold bias will increase clean overhead, but it will also reduce volume... it's all about area under the curve, and a square wave of the same amplitude (assuming the same B+ voltage) as a sine wave has a LOT more area under the curve.

The Blues Junior is indeed a fantastic amp, and more versatile than "traditional" Fender amps of yesteryear that simply did not do "dirty"... it's just a matter of working with the amp and learning its limitations and strong points.
If you need "loud-clean" for a larger club, then something like a Blues Deluxe or DeVille (or one of the Silverface reissues) would be more suitable... it all depends on how much clean top end you need.

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