Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: vampwizzard on February 19, 2019, 04:59:44 pm
-
I learned a lot last build taking an AO-39 to a Matchless Spitfire, now I want to try converting one from my collection into a Gibson GA-25RVT Hawk amp. Schematic here: https://images.gibson.com/Lifestyle/Support/Files/Schematics/Hawk.PDF (https://images.gibson.com/Lifestyle/Support/Files/Schematics/Hawk.PDF)
Ill opt out of reverb although I do have a spare tank.. Im more interested in building this because I haven't built a negative feedback amp yet. B+ Voltages seem to be a perfect match. Trem seems stupid easy.
Step one is to revise the schematic to include a few modifications: Single input, variable NFB, and ill probably replace the weird Gibson voltage dividing network that attaches to the wiper of the volume pot with a .02 cap (a common mod/fix for these amps). Ill probably strip this chassis bare and clean it up. possibly paint it. more cosmetics work here and with the cabinet. the spitfire conversion was all birch plywood and this one will be dimensional lumber for the box and ply for baffle/back panel.
May set up a poll if yall are interested in choosing the color for this one. Should be fun.
-
Heres my modified version of the schematic. Notes are made for the modifications. "Tone suck" replaced by a .02 cap, which may become a .01 cap, replacing the tremolo depth resistor with a 250K pot, adding bypass resistor/cap to the trem tube a-la the traynor 1 tube schematic, and my estimates for the power section resistors.
-
Theres an error in the trem schematic. The depth pot needs to be wired as such.
-
> depth pot needs to be wired as such.
Why? What is wrong the way you had it?
-
Theres no voltage dividing going on as original. See GA18T