- Big_sby
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Custom Top utilisateur
papycognac a écrit :
mon BJ a actuellement deux lampes 6BQ5 en puissance. J'ai lu précédemment dans ce topic que les JJ ou les EH EL84 sont pas mal. Est ce que EL84 est pareil que 6BQ5 ? Si je prends des 6BQ5 d'une autre marque que celle déjà installée, dois-je regler le biais?
le Blues Junior est un Cathode Biased qui ne nécessite donc pas de réglage du bias après un changement à une condition c'est que le duet de 6BQ5 EL84 soit matched c'est à dire qu'ils soient appairés (mêmes valeurs).
certains "customisateurs" proposent des kits permettant de régler le bias :afin d'assainir, affiner le son de ces petites boites, mais c'est un upgrade.
ceci dit à l'usine, les BJ sont réglés Hot, ça permet de mettre "tout ce qu'on veut ou presque" mais ça peut aussi donner un son Muddy, Overtone... aigu, cassant et pas très harmonieux et dans certains cas (je ne connais pas la parité) faire "jouer" les tubes trop chaud et donc les user plus rapidement.
ceci dit dans la majorité des cas, et ceux qui l'ont poussé et / ou joué LIVE ne me contrediront surement pas, cet ampli sonne si "particulier" si "grand" car il est biasé hot, et de plus en plus de gens ici s'aperçoivent que le biaser plus doux avec la modif à Bill entre autre, c'est pas ce qu'il y a de mieux... et j'en ai parlé avec des gens sur les forums américains et après sur la scène lors de jams entre autre
moi je l'aime biasé usine cet ampli.. il donne cette impression qu'il va exploser littéralement, ce qui lui donne ce son crêmeux si néo vintage... et pour infos mon potard d'aigu est à fond tout le temps, et ça sonne super chaud, doux... de la crême.
voici un de ces avis :
I get almost daily inquiries about the VERY popular Bill M. mods for these amps so please note, the following is simply my opinion and will not be shared by everyone!!!! (Sorry Bill)
While some of the Bill M. tone mods are nice I completely disagree with his theory on correct bias for these amps. The BM bias mod will suck the life and tone right out of the amp. I can't tell you how many players have called me wanting tubes that will breath life back into their Junior's and Pro's and during the conversation they will fess up to the BM bias mod. This mod will get the bias way too low. Players like these amps because they sound good right out of the box and they are biased hot which gives them a great juicy tone with a very good dynamic response so my recommendation is to leave the bias as is and make sure that who ever you buy your tubes from knows what the tubes are for and grades their tubes. Hopefully they will also know something about these amps too.
Both the Blues and Pro Jr's are fussy about phase inverters and need a good balanced tube for V3 to get them smoothed out. Most Fender amps respond very well to the JJ ECC83S's and these amps are no exception, in fact they respond extremely well to them."
Source: http://www.eurotubes.com/euro-l.htm#1
frank62
MAINTENANT QU'EST CE QUE LE CATHODE BIASED
"When do you use fixed biasing instead of cathode biasing?
Since cathode biasing eliminates the need for a special negative DC bias supply, why don't all amplifiers use cathode biasing? Well, cathode biasing is not without its faults. It turns out that in order to keep the DC bias supply voltage at the cathode constant while the input signal is changing, the cathode resistor must be bypassed with a large capacitor. This capacitor effectively "shorts" the AC signal component to ground, while allowing the DC voltage to remain relatively constant. If the capacitor is removed, the cathode DC voltage will have a signal voltage superimposed on it, which will subtract from the grid-to-cathode signal voltage, and reduce the gain of the stage.
The problem comes in when there are large signal level changes, and the average DC level of the cathode voltage changes. This causes a bias shift, usually in the direction of a colder bias point. This bias shift can be audible, but is sometimes desirable for guitar amp use, as it adds varying harmonic overtones to the sound. If the bias shift is severe, the tube will go into cutoff, and large amounts of "crossover" distortion will occur. In addition, the current flow through the cathode resistor generates a necessarily large bias voltage on the cathode for proper tube operation (typically 30-50 volts for most higher power output tubes). This voltage subtracts from the total plate voltage, which decreases the available output power. Between this voltage decrease and the bias shift, the output power in cathode biased operation is reduced when compared to fixed bias operation. Therefore, fixed bias is usually used for higher power amplifiers (50W and higher), and cathode bias is usually used for lower power amplifiers.
Preamp tubes are almost universally cathode biased, because they are used for signal amplification, not power amplification, and the side effects of cathode biasing are not as important. Also, cathode biasing makes the circuit less dependent on tube parameters, and more forgiving with respect to bias point. This allows replacement of tubes without having to rebias the amplifier stage. Output tubes that are cathode-biased should always be checked when replacing tubes, however, because they vary widely in terms of idle current for a given cathode resistor value, and it may be necessary to change the cathode resistor value to return the output stage to it's proper bias current."
"It may take talent to play fast, but it takes SOUL to slow down and say something....."
“What the guitar does not produce
cannot be supplemented electrically.”
– Yasuhiko Iwanade, The Beauty of the Burst
“What the guitar does not produce
cannot be supplemented electrically.”
– Yasuhiko Iwanade, The Beauty of the Burst
