The BitMo Sufra mods work with both the head and combo versions of the Jet City JA20. While retaining the standard configuration, the mods solve some issues and add very useful features (controlled by 2 added front panel switches) which make the amp much more versatile. I have heard complaints that the amp lacks clean headroom and punch, and can get a bit fizzy. With these mods (and maybe changing a tube or 2) you can fix these issues and have a really great amp at a fantastic price!
With both switches off, you have the stock configuration.
The 1st switch adds loud clean headroom and punch by partially bypassing the congested M*style tone stack. This setting is great for those who like to use pedals.
The 2nd switch slathers on a dollop of fatback overdrive that can go from that famous BitMo chocolaty brown cello sound to a tight, biting boost. It is like having a Screamer-type overdrive in the middle of the gain structure.
The switches can be used separately or in combination providing very touch sensitive new voicings which are great across the full range of the gain control settings going from warm or sparkly clean to balzout overdrive with lots of interesting shades in between.
I do recommend changing the V2 preamp tube to a 12AT7 or other lower gain tube and V1 to your 12AX7 flavor of choice.
Warnings, etc: There can be some dangerous voltages in tubes amps so be careful! Always unplug the amp while working on it. You should also use goggles or glasses while soldering. I disavow any responsibility for damage, injury or lost hours. The instructions are simple enough for a novice. You experts should be able to figure it out. Skills needed - must be able to solder and drill a hole in the metal chassis. Tools you will need - screwdriver, knife, soldering iron, rosin core solder, wire stripper, needle nose pliers, drill and bits.
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Warranty Information and Return Policy
Warranty Period: 3 months
All our tubes are guaranteed for 3 months from the date of purchase. (Any exceptions will be noted on that tube's Warranty tab)
If you receive a tube that does not perform to the manufacturer's specifications, please do the following:
- contact us to get a return authorization - return it via regular mail within 90 days from when we shipped it, and we will provide an exchange or refund of the full purchase price of the tube.
Returns not related to warranty or defect will be considered at our discretion, and are subject to a 15% restocking fee.
We can not accept returns that don't have an authorization, are past 3 month, or are returned improperly.