Burns Orbit Three

[Jazz P Bass]

I have some AC107 Germanium transistors .
https://www.radiomuseum.org/tubes/tube_ac107.html

[Richardvet]

Hi, new to this forum since I was looking for info on Baldwin-Burns guitar amps. I have a BB Orbit 75, which appears to be an uprated version of the Burns Orbit 3. Two 12" Fane speakers, probably about 65-70 watts??? I found the Orbit 3 schematic on this site, and have edited this with the Orbit 75 differences (basically the channel 1 tone selector is now a standard bass tone control, as per channel 2). It appears that Baldwin took the Burns Orbit 3 and just increased the first rail voltages from 33 V to 43 V, without dealing with the power stage as far as I can make out. I have derated my Orbit 75 to Orbit 3 specs to stop it over-heating (several components were heat-damaged, hence me buying it as non-working). I have attached the Orbit 75 schematic, but it still needs some work since the Orbit 75 has both treble boost and studio boost buttons and I haven't figured out how they work as yet. The schematic represents my derated version of the Orbit 75 (R64 and R72 have new values to get the correct Orbit 3 rail voltages). The patchwork quilt effect on the schematic is a result of real cutting and pasting to produce the Orbit 75 circuit from printouts of the Orbit 3! I have recapped the entire amp, plus replaced the heat-damaged resistors and tracks. The amp has gone from a scratchy crackly dull amp to a really nice sounding amp, which due to the interstage transformer has a tendency to sound a bit valvy at times (guitar on 10). I have also replaced the EI transformer with an 80 VA toroidal and fitted a plastic main power switch as per today's regulations.

[Richardvet]

Hi. Update on the Orbit 75, just in case anyone’s interested! It has 3 boost switches, which have the following actions: #1 bass boost which alters the knee of the tone control filter, #2 treble boost which agains alters the knee of the tone control filter plus alters bias to TR7, #3 studio boost which works the same as the Orbit 3 by changing the gain of TR8.