The Epiphone Valve Junior head is a 5-watt amplifier that connects to an external speaker cabinet. It has the notable characteristic of featuring only a volume control. It's a simple-to-use piece of class-A equipment. Class-A equipment is defined by having one amplification stage, which means the output signal is an unaffected, louder analogy of the input signal. No gain, equalisation or modulation is added to the signal. Because this is a budget amplifier made with cheaper parts, you might want to mod some of the parts to improve the general sound quality.
- Skill level:
Things you need
- Soldering iron
- Replacement tubes
- Replacement power transformer
Plan your mods on paper. It's important to plan exactly what you intend to do with the amp, rather than simply tinkering with the parts. The Epiphone Valve Junior head is prone to humming; fix this by replacing the capacitors and attenuators in the power supply.
Acquire your parts. You can get most of the necessary parts from an amp-kit retailer. You can save money by salvaging your parts from old or broken amps, although this process takes much longer.
Inspect your parts. If you spot any cracks in the steel parts, such as attenuators or potentiometers, discard and replace them.
Remove the preamp. Use a screwdriver to unscrew the rear panel of your Valve Junior. This exposes the preamp section of the head. Slide it towards you gently, so that you can access the wiring. Melt the solder joints with a soldering iron to disconnect the wiring and then put the head chassis to one side.
Slide the power section toward you for easier access. If you wish to remove it completely, melt the wiring connections.
Unscrew the existing attenuator from the chassis. Look for the large metal component sitting furthest from the input socket in the signal chain. Unscrew the attenuator and melt the solder joints. Fit the replacement in place, reconnect the wiring and screw in place. Capacitors are fitted to the circuit board by a pin, so simply pull them out to replace them.
Replace the tubes. Make sure you are replacing a power tube with a power tube and a preamp tube with a preamp tube. Pull the old tube out of its housing and slot the new one in its place.
Reattach the power amp. Reconnect the wiring with a soldering iron and gently slide the power amp back in place. Then do the same with the preamp before enclosing the back.
Tips and warnings
- Clean the inside of the amp, especially behind the potentiometers, while you have access.
- Replacing the tubes is a good way of increasing or decreasing the gain. The Epiphone Valve Junior has two tubes: One 12AX7 and one EL48. You can alter the tone of your amp by selecting higher or lower gain tube replacements. The Tube Store website has a gain factor conversion chart that illustrates which mods are suitable for your current tubes.
- Always ensure that the amp is disconnected from the power before attempting mods. Leave the amp to cool before moving it if it was previously in use.
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