HB GA5 / Epiphone VJ 5E1 Mod
The Epiphone Valve Junior and the Harley Benton GA 5 are almost identical in construction, but there are slightly different versions. This is one of my first instructions on the net and it still works. In the picture you see various devices for which this modification is useful. I prefered the GA5 because it already had the hole for the tone control.
The modification is essentially based on a Harpgear HGII. Changing the speaker is not necessary. The Epiphone can be purchased with various speakers, so it might be different there.
The example shows the board of version 2, which is used quite often. Still without any changes. You can see the small board at the tone control, this one is missing at the Epiphone and on the board is a wire jumper. That's not bad, because it is a stack from which the bass control comes out. This makes little sense at 8".
Therefore, we first remove the board (disconnect it at the GA5) and bridge the connection to the power amplifier (5). The points (3) and (4) can be used to insert a highcut. Here with a shielded cable.
That already was the biggest change. Only changing a few more components:
1) 1M 2) 33k 3)2,2k 4) 1,5k
5) 22k soldering on the existing bridge and connect it to the brown connection of OTs
6) bridge in the picture, use 220k if applicable
7) 0,1uF 8) 0,1uF 9) 56k 10) are omitted
11) 22n with a 500k log between the black and white wires of the volume
We take a 12AY7 as a preamp tube like Harpgear does. The result is great. Martin from Vienna plays the GA5 against his Harpgear HGII.