Epiphone Valve Junior.... MODDED!

Before..


After...

from left, hi-lo gain switch, gain pot, input, volume pot, master volume pot

So i bought a new amp bout three weeks ago for a price of 1k. A Single Ended Class A Tube amp called Epiphone Valve Junior. It may be just 5 watt, but it's still VERY loud! Anway, when i planned to buy this baby, it was with a great intention of me to mod it myself to get a hold of tube amp cicuitry/technology. I managed to mod my MT-2 and TS9, so why not upgrade my skills to tube amp!

Before anything, in a tube amp circuitry, there are Filter Capacitor that has a very high voltage and without proper safety, the capacitor may discharge itself to YOU with a VERY HIGH VOLTAGE and MAY KILL YOU!

However, in this EVJ, there lies a bleeder resistor where it will bleed out the charge after the amp being turned off. Following some people's advised, its best to unplug the power chord off the back of the head, switch the amp power switch to ON and just leave it be for about 5 minutes or more to let the caps drain..

That being said, sewatt.com was the main forum i used as a guideline for doing the mods. I followed mostly the 'Marshal Silver/Gold' mod, with added gain control and a Master volume. Components are bought from Nik Azam at Ceriatone.

The first mod i did was changing the cathode bypass caps for a better and tighter bass response which is C3, C4 and C5, to 1uf 25v, 1uf 25v and 1000uf 50v respectively. But then, when i switched it on and plug in my guitar... There was NO sound AT ALL!! I tried to be as calm as i can while asking around at sewatt.com and at jamtank.net. Bought a multimeter right away and learned using it to check continuity with the ohmmeter mode coz the damn multimeter doesn't have a 'Beep' feature for continuity checking! The tubes didn't even glow when i turned it on! After bout three days of troubleshooting and listening to advices, i was kinda gave up and decided to send it to a pro, keysorseze from jamtank.net. But then, Cgil from sewatt.com saved me! It was just a simple common problem of EVJ, that is the fuse contact. So i rubbed 'em a bit with a sandpaper, put the fuse back in, plug the power in and switched it on. My face gradually lighten up as i see the filaments of the tube glowing! and when i plugged in my guitar.... Krrrangggg...

Ahhhhh, such a sweet sound...

Then, i proceed with next set of mods. Long story short, these are what i did..

R4= 1ook ohm Carbon Comp
R5 = installed a 500k pot, wired parallel to the stock 220k ohm with the middle lug connected to one foot of R15
R6 = using on-on DPDT to swich it between a wire (jumpered) or a 680k ohm 1 watt (happen to have this around)
R10= 1k 6watt
R15 = 10k 1 watt
c3 = 1uf 25v
c4 = 1uf 25v
c5 = 1000uf 25v

Its been a week since i mod this EVJ. Wanted to give it a week evaluation before i tweak it more. The amp now has a more tighter bass response although too little. It also kinda lack a bit presence i think. I like this master volume pot coz i managed to dial in quite a variety of tone by playing it along with the stock volume control (which is now a preamp volume control). The R6 swicht, which i called high-low gain switch is also a great addition. With R6 jumpered, the gain would be high. This is where i used with my modded MT2 to get crunchy heavy distortion sounds. The low gain (680k), i usually use for clean sounds. Overall, its an upgrade of the stock but still need some tweakings.

Bought some components from jalan pasar to tweak it a little bit more. i'll post about it when its done. And, oh, i'm still using the stock tube which is 12ax7 EHX and Sovtek EL84.

All and all, it's a great learning experience! especially the troubleshooting!



inside!


the schematics..