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Anyone there playing there Epi with a Blues Junior ?


Big Norm

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I'm thinking to buy a Blues Jr to replace my Marshall AVT 50 for giging...I have to say we are playing mic all the time ( since th Jr is only 15 watts ) but I found my Marshall sucks a bit, and I'd like to replace it with a Blues Junior or Peavey Custom... What are your experiences with those amps.

15 watts does'nt sound to heavy, but I read a lot of good comments on this amp and is power. My main guitar is an Ultra, and I really think she needs a real tube amp to perform.

I will "roadtest" it tomorrow.

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I think you could have enough clean headroom to gig with.. and certainly you can loop or put a pedal in front for higher gain stuff.

 

I had a hot rod deluxe.. way too loud for home playing.. and now almost 200.00higher priced than when I had one.

 

An epi vj will play with a reasonable drummer.. so I think 15 watts will do you for clean and distortion.

they sound pretty good, to me.. not quite a blackface deluxe but hey. not as much money either..

 

find out what speaker is in the stock cab.. you can make a huge difference there..

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or be a little more patient.. check out the price of an epi valve senior at sweetwater.com

 

18 watts reverb class A etc etc etc...

that's 359.00 with an eminence lady luck tuned to the amp....

compared to the blues junior price... the epi vsr looks to be some serious competition for tone and value!

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Hi Norm...I regularly gig with a Blues Junior. Usually run a Riviera, Gibby LP Double cut, and Rickenbacker 12-string,

or Highway 1 Strat and Telecaster through it. It's never let me down! I use pedals (OD, Comp/Sustain, and a Rotary) when needed.

We play in small clubs, and bars, mostly (unmic'd). It's plenty loud!!! I have a Hot Rod Deluxe, and

Twin Reverb, for bigger venues, but the BJ is a great little amp, and would be fine, mic'd, for larger

places, too. My fellow guitar players use Peavey Classic 30's, and the BJ keeps up with them, just fine.

One of them, has a BJ too, and he has about decided to go back to that amp, as he likes

the tone, "much better"(his words). I love the HR Deluxe, as well....but it's "Sweet Spot" is just too

loud, for most of the venues I play in, these days.

 

Hope that helps, some?

 

CB

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Oh, I did change out the speaker, to a Celestion "Vintage 30," in the Blues Junior.

There was nothing wrong (technically) with the stock speaker, but the Vintage 30 really

tightened the tone up, and allowed it to "sing," as well. So far, that's the only "mod" I've

done to the amp.

 

CB

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I have to say,i`m loving the Epi Amps.I`ve used a Marshall for ages,then it started to die on me.After talking to Svet about my options,i settled on the Blues Custom.First Gig with it last night and it was flawless.I suspect the Blues Junior will be the same.Great Amps,and thanks to Svet for the advice.

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I didn't really know how loud a 15 watt amp can be. If you are pushing it with humbuckers it can get really loud. Havng both a volume and master volume, you can dial in some nice overdrive.

The way gas prices are going through the roof, Im going to take the BJ with me me when I go shopping for a Smartcar.

Got to be sure it will fit. I will have to buy a second one to haul my guitar.

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The Epi Sr. is showing on Sweetwater as a Class A/B push-pull tube amplifier.

 

What does that mean as opposed to a class A tube amp? Is the Blues Jr a class A amp?

 

Dear Sir(s). Here are some Randall Aiken's - www.aikenamps.com - Technical Infos - Q & A: Q: Is it true that the only true class A amplifier is a single-ended amplifier?

A: No. You can design a true class A single-ended or push-pull amplifier. The presence of a phase inverter tube does not automatically mean the amplifier is class AB, just as the presence of a cathode resistor doesn't automatically mean the amplifier is class A. It is all a function of where the output tubes are biased, and under what voltage/impedance conditions they are operating. In fact, unless you know the plate voltage, plate bias current, and output transformer reflected impedance, you can't tell the class of an amplifier just by looking at the schematic. A push-pull class A amplifier differs from a single-ended class A amplifier tonally in that it cancels even-order harmonics generated in the output stage (but passes through even harmonics generated in the preamp stages, of course). It also has inherent power supply rejection for lower hum and noise levels than a single-ended class A amplifier. Typically, a push-pull class A amplifier will clip rather symmetrically, while a single-ended class A amplifier usually clips asymmetrically, most often rounded on one side while hard-clipped on the other. While both amps are indeed true class A amplifiers, their tones are dramatically different. This further illustrates the fact that there is really no such thing as a "class A" tone. and Q: Any time one tube or set of tubes is said to be "pushing" and the other "pulling" inherently, the amp is not operating Class A, right?

Not true. In a true class A push-pull amplifier, one tube is indeed "pushing" and the other tube is "pulling", but neither reaches cutoff at any point up to the unclipped full output level.

 

The difference between a class A push-pull output stage and a class B push-pull output stage is primarily the bias point. The class A output stage is biased in the center of the linear portion of the transfer characteristics, and the class B output stage is biased at cutoff.

 

In a class A amp at idle, with no signal present, each tube is drawing (ideally) an amount of current halfway between cutoff and saturation. For example purposes, let's assume this is 100mA, and assume the plate voltage is 250V. The tube is therefore idling at 250V*100mA = 25W. Now, if a signal is applied to each of the two output tubes from the phase inverter, one tube's current will increase and the other tube's current will decrease by the same amount (because the phase inverter generates two drive signals that are 180 degrees out of phase).Let's assume that the input signal amplitude is enough to drive the first tube to 150mA - in this case the second tube is now at 50mA, because it decreased by the same amount as the increase of the other tube. Taken to the limit, if the input voltage is enough to drive the first tube to 199mA, the second tube will be driven to 1mA, which is right at the limit of cutoff. If this is the maximum clean output of the amp, and the saturation point occurs at 200mA, the amp is operating in perfect class A, because neither tube has ever hit cutoff or saturation up to the maximum clean output of the amp. The output transformer sums these two complete, unclipped, out-of-phase sine waves to generate a sine wave of twice the equivalent level of one side (this is how you get twice the output power of a single tube running class A single-ended).

 

If you average the current draw over the full sine wave, the increases and decreases cancel each other out and the average current is the same as the idle value, or 100mA. Therefore, there is no change in the current drawn from the supply. The plate dissipation in a class A amplifier output tube goes down with applied signal, because as the current goes up, the voltage goes down, and as the voltage goes up, the current goes down (inverting) and the power dissipated in the tube is the product of the voltage multiplied by the current. At the extreme, when the current is zero and the voltage is at max, the instantaneous dissipation in the tube is zero, and at the other extreme, when the voltage is zero and the current is at max, the instantaneous dissipation is also zero. Since the average plate dissipation in the tube decreases, the tube can be biased at the max rated power at idle.

 

In a class B amp, since the tubes are biased at 0mA, one tube will increase to a maximum as a signal is applied, but the other tube will stay in cutoff until the second half of the input cycle. Then that tube will increase in current while the other tube stays in cutoff. These two "halves" will sum together in the output transformer to make a full cycle. Since the tubes aren't perfectly linear in the region near cutoff, there is a type of distortion introduced called "crossover distortion", caused when the two tubes "hand off" operation to each other. Because the tubes are in cutoff for half of each cycle, the average plate dissipation is much lower than it is for class A, so more output power can be obtained from the class B configuration.

 

Class AB operation is obtained by biasing to a point in between class B and class A. for a portion of both half cycles of the input sine wave, both tubes are conducting current in opposition as in class A, but one tube hits cutoff before the other tube hits saturation. The other tube's current keeps increasing up to a maximum, and back down to the "changeover" point, which is above the zero current point. The maximum output power is less than in class B, but more than in class A. The distortion is less than in class B, but more than in class A. Most push-pull guitar amps run in this class of operation.

 

In a class AB or class B amp, the power dissipation will increase or decrease depending on operating conditions and applied signal level. This is why they have to be biased at a lower dissipation than the max rating of the tube, typically 70% max. If you bias them at the rated dissipation, they will be fine at idle, but they will run too hot when you start playing.

 

Q: I'm still confused about this "class A" stuff - how about a more general explanation?

A: The general idea is this: Picture a sine wave going positive above zero volts and then negative below zero volts. The way the tube is biased and the circuit is set up determines when the tube (or tubes) is on. It gets a bit shaky when you are dealing with push-pull, which uses tubes in pairs (or quartets, or more, always in multiples of two), or single-ended, which uses one tube (or more, but they are in parallel with the first one, not in push-pull).

 

Class A: All tubes are "on" for the entire sine wave, in either single-ended or push-pull. In single-ended class A, one tube (or two or more in parallel) amplifies the whole sine wave. In class A push-pull, one tube is "pushing", while the other tube is "pulling", but they are both on for the entire waveform. In push-pull class A, one tube amplifies the sine wave, the other amplifies an upside-down version of it (180 degrees out of phase), and the two complete signals are added together in the output transformer to produce a new sine wave of higher power than you could get with a single tube in the single-ended configuration. This class of operation is characterized by high-linearity and low distortion, which makes it ideal for audiophile-type gear, and very low efficiency (DC power in vs. AC signal out), which means you don't get a lot of watts for your money. All single-ended output stage guitar amps operate in class A mode.

 

Class B: This class is usually used for push-pull only, although you could have a single-ended class B amp, but it wouldn't sound very good for audio. In class B push-pull, on the top half of the sine wave, one tube is on ("pushing"), while the other tube is off ("idle"). Then, on the bottom half of the sine wave, the other tube is on ("pulling") while the first tube is off ("idle"). Essentially, one tube amplifies the top portion of the sine wave, while the other tube amplifies the bottom portion. The two "halves" are added together in the output transformer to make a new, completely-whole sine wave, so there is no clipping caused by the amplification of only half the wave by each tube. This mode is characterized by very high efficiency, so you get more power than you can in class A, and a type of distortion known as "crossover distortion", which is caused by the non-linear overlapping of the turn-off and turn-on times of the tubes.

 

Class AB: This class is sort of in-between class A and class B, where the tubes are biased higher than class B, but not as high as class A, so one tube still turns off at some point in the sine wave, but not at the exact zero crossing. This allows more "overlap" in the two halves, so there is little or no crossover distortion, but the efficiency is still much higher than class A, so you get more watts for your buck. Most push-pull guitar amps operate in class AB mode.

 

Q: You recommend biasing the Intruder 30 watt head to 45mV - 50mV on the dual external pots which corresponds to 45 - 50 mA per side. This is loaded with a pair of EL34's. Is this specific to his head and others like this?

A: Yes, that is specific to the Intruder (and Invader) 30W head, which runs very close to true class A push-pull, at around 300-320VDC on the plates.

 

You can't just set the bias of a particular tube to "xx mA", without taking into account the plate voltage the amp is running at, and in some cases, the design of the phase inverter.

 

Higher plate voltages generally require lower bias currents to keep the tube running in the safe dissipation area. This usually means the amp is running in class AB or, if the plate voltage is extremely high, class B, with the tubes biased at or near cutoff because of the high plate voltage involved. If the amp is running class A, or very near, you can bias it much hotter, as is the case in the 30W Intruder.

 

The other thing to take into consideration is the phase inverter output voltage swing. As you adjust the DC bias voltage, you also are adjusting the baseline negative DC voltage level of the drive signal to the grids of the output tubes. If you set the bias for less current, what you are actually doing is raising this negative DC baseline voltage up towards ground.

 

As you raise this voltage, you are effectively limiting the headroom of the signal, because it will clip when the peak voltage hits zero volts. If the phase inverter is designed for a lot of gain/output voltage swing, it will distort very early and possibly go into "blocking" distortion because of the clamping action at the grids of the output tubes when the signal hits zero volts on the peak. This can sound "mushy", so you must bias the amp colder to compensate. In the case of the 30W Intruder, the phase inverter output voltage swing is designed to be lower than a 50W amplifier of similar design.

 

The bottom line is this: you can't just arbitrarily say that any tube should be biased at some particular range of currents, because it depends on the circuit design of the amplifier. The manufacturer should provide the specified biasing procedure for the tubes suitable for use in each particular amplifier.

 

Q: A class A amplifier's tubes are is working at full power all the time, whether it is sitting at idle or playing full blast, right? That's why the tubes don't last as long?

A: No. Contrary to common misconceptions that are quoted in all the magazines, a true class A amplifier is not running at full power all the time, whether at idle or full output. The plate dissipation of the output tube (or tubes) is usually highest at idle (they are typically biased to max dissipation, or even slightly higher in some guitar amps), and the plate dissipation decreases as it starts delivering power to the load. In other words, the power that is dissipated as heat in the tubes at idle is passed on to the load at full power. If the output is a pure sine wave, the dissipation splits evenly between the tube and the load. For example, if an EL84 is biased at 12W idle in true class A, it will put out 6W into the load at full power (assuming no other losses, for this example), and the tube will dissipate 6W at full power. As you can see, the tube's actually run cooler at full power than the do at idle in a true class A amplifier. In addition, if the output is a square wave instead of a sine wave, the tube's dissipation will be zero at full power, and the load will receive the entire 12W (ideally speaking, ignoring other losses and assuming a purely resistive load). This is because the plate voltage and plate current in an output tube are 180 degrees out of phase, so when the plate voltage is at max, the plate current is at zero, and vice-versa, so the instantaneous power, which is the product of the voltage and current, is zero at all times.

 

Q: Class A watts are different from class AB watts - they're louder, right?

A: Absolutely not. This is a common misconception put forth by people who don't know what the hell they are talking about. Watts are watts, and they are completely independent of the class of operation of an amplifier. The proper way to measure and amplifier's maximum output is at the onset of clipping into a purely resistive load. Apparent loudness is a different subject entirely, and depends on a lot of factors

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You are going to have to play one with your guitar and see what you like. I had one of the limited tweed BJs with the speaker upgrade and never liked it took it back within 30 days. Always found it harsh sounding.

 

I have a Laney VC30 and love that. It sounds to me like a cross between a Fender and a Vox. The EL84s have a sweet distortion/break up. I thought I would like the BJ based on my Laney but did not.

 

Everyone has their idea of the perfect tone. If looking at BJs then try the Super Champ. Has a 10" speaker vs 12" in the BJ but 6V6s so slightly higher power output.

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