NAD - Harley Benton GA5H / Epiphone Valver Jr head

[waltschwarzkopf]

Hello, World!

I just picked up this lil' head over the weekend. It is a single-ended 5W all tube (12AX7 + EL84) head. The sound on this thing is unveliebable, very clean sounds at low volume, some dirt close to 12 o'lock and natural overdrive when you crank it up!

I played it through a 1x12" and a 2x10" boxes and it sounds very nice. I got this head to mod, but since I like the sound so much, I don't want to change much anymore.

• Initially I wanted to activate the tone stack and at Bass-Mod-Treble knob, but the EQ (Bass/Contour) does an excellent job. So I may ad the BMT later just to try.
• The volume control (actually gain) also works well, but in otder to get crunch one has to play fairly loud, so I may add a master volume.
• While I'm at it, I may add a stand by switch to keep the tubes warm when not playing. (Anybody knows how to do this?)

I found a site in which they did some mods, so I may use as reference (see schematic below). Still, I have some questions:

1. The R1 / R2 array, looks like a voltage divider, meaning that this reduces the signal coming from my guitar, right? I see that it has been removed, along with R5, which I guess works in a similar way. According to the blog "I removed the R1 and R5 resistors. This mod made the amp much more versatile in terms of tone and headroom. But there just wasn't enough headroom!..."
2. They also added a bypass switch for the EQ, that I am curious to try and see what the amp sounds like raw, this should also make it louder., right? "...That's because there was a huge voltage drop across the EQ tonestack and the power amp sounded like it was 2W instead of 5W... So we put an EQ bypass switch in there to compensate for the signal loss when volume and extra power is required. The EQ bypass switch is placed between the R19 and the ground."
3. A master control may be the only missing thing from this head, so I may do exactly what they did. But does it HAVE to be a 1M log pot? I cannot seem to find one, so I may borrow the one from the EQ. " We decided to add a 1Mohm "master volume" control before the el84 and keep the stock "volume" control as a gain pot."

The amp seems to be mounted on an oversized chassis, so I may combine it with a 1x12" cab that I'm building and make it into a combo!

What do you think?

Cheers,
Walter

[waltschwarzkopf]

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