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Epi Valve Junior Tube amp....Say What!!!!

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from http://www.aikenamps.com

What does "push-pull" mean? A: This allows the tubes to conduct on alternate cycles of the input waveform

A push-pull stage can be biased class A, where current flows in both tubes for the entire input cycle or class AB, where current flows alternately in both halves, but less than a full cycle in each

A push-pull stage requires at least two tubes to operate


What does "single-ended" mean? A: A single-ended guitar amp output stage is generally biased class A, in order to maximize the output power before distortion. The single-ended stage is the type of output stage used in the venerable Fender champ guitar amplifier and countless millions of others.

It is as inefficient as it is good sounding, putting out very low power levels in comparison to push-pull output stages.


Disadvantages of single-ended include: no rejection of power supply hum, which mandates heavier filtering to keep the hum to acceptable levels, no rejection of even order harmonics (a great advantage to guitar players!), and generally asymmetrical limiting on overloads which further emphasizes even order harmonics (which are more pleasing to the ear than odd order harmonics). These "disadvantages" give the single-ended output stage a unique tone, compared to the push-pull output stage.


Whether it is "better" or not is a matter of taste. Some guitarists prefer single-ended output stages, others prefer push-pull.

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"single ended" refers to there being only one output tube. All single ended amps are class A, because the output tube is working 100% of the time. Very few amps, besides single-ended amps, are true class A, although those that claim to be tend to sound very similar.


In a "push-pull" amp (class A/B in guitar amp world), the output tubes alternate pulling the load. A class A amp will typically burn through tubes faster than class A/B because of this.


Class A will produce more even harmonics as it distorts than class A/B. This translates into what could be called a "sweeter" distortion, while A/B distortion could be called "more complex/thicker/more swirl."

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I've got a couple of Vintage class A amps that have had the same tubes for years... My 1st Version 1 VJ was "hammered on" almost every night for an hour or 2 and those tubes are still going strong according to the new owner (sold that one). Don't let "sooner" scare ya'. Besides there's only 2 !!!

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...' date=' you say that in a class A amp the tubes burn out quicker. So how quick is quicker?[/quote']

I've been loosely tracking tube life on my VJr. V3 --- up to around 180 hrs. on Tung Sol 12AX7/ECC803S and JJ EL84 and going strong. Paid $26 --- that's only 14.5 cents an hr. (& dropping daily) for ENTERTAINMENT THIS GREAT!! ](*,)

(edit - BTW most of the 180 hrs. are at 1 o-clock-to-max level and about 1/2 w/distortion pounding the front end)


When I bought VJr. I had concerns about tube life (some recommend that voltage lowering mods are necessary) but for my part at 180 hours plus+++ why not save time, save hassles, just play the thing. It's definitely the most cheap fun you can have in a $149 electric guitar tube amp -- Thanks Epiphone!


Hit every BLUE NOTE baaaby..., I'm going to play on:-"

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you say that in a class A amp the tubes burn out quicker. So how quick is quicker?

That depends entirely on the amp, the tubes, how hard the amp is played, and how often it's played. There is no hard fast rule that fits everyone. Preamp tubes don't generally wear out, however. It's output tubes that do the majority of the work and get hammered the hardest. It's not at all a bad idea, however, to try out several different preamp tubes, to see what you like best. Especially in a SE amp like the Vjr, where you've only got one of each...dramatic changes in tone can be heard just by swapping that preamp tube.


You'll likely not hear output tubes wearing out, unless you know what to listen for. Until/unless they short out or go completely gassy and start making alien noises, they'll just keep working, even though they may be well beyond their prime. The only way to know for certain that a working tube that's been working for a while is actually good is to remove it and test it thoroughly. Short of that, you could have a tube that's completely anemic, and on the verge of not even being able to conduct anymore, that still "works." You can't assume that just because a tube is still glowing red, it's any good.


If you know of a decent tech in the area, he won't likely charge much to test tubes for you periodically, and he'd be a great place to buy replacements from when needed as well. Once you get familiar with the wear patterns of the tubes in your particular amps, you'll be able to get on a bit of a schedule, as to when they'll likely need replacing. Until then, it's nothing but a guessing game.

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