BACK FROM THE SIXTIES

Burns Orbit Three

There are four different versions of this unit:

881 and 882 (reverb): 'Orbit Three'  3 x 10"

885 and 886 (reverb): 'Orbit Three Double 12'  2 x 12"

Dimensions:

21"h x 25"w x 10"d     Weight approx 37Ib

Advertised output power:

NB: The Orbit Three Double 12 is not the same thing as an Orbit Double 12

Actual measured output power at clipping with 240v ac mains supply:

60watts. Although it's not specified in the brochure, this is peak power.

33watts rms into 2 ohms

25watts rms into 4 ohms

Burns used a number of different circuits in Orbits, so it's pot luck whether the schematics apply. Problems finding replacement parts and service information (and the rats nest wiring) have probably contributed to the number that have been abandoned or broken up for spares rather than repaired. Shame, because they're great sounding amplifiers when they work.

Latest to turn up is a 3 x 10" that's been thrown down the stairs, buggered about with and stripped. To say it's beyond economic repair would be to say that Ming The Merciless was a bit naughty but, luckily, it still has enough of the original components to work out the circuit and layout,

Don't be put off if the drawings don't match exactly. It should be possible to pick enough info from different versions to get the job done. Expect to find melted sleeving and back to front electrolytics from the factory, as well as multiple dry joints and fifty years worth of abuse. The resistance wire in the output device emitter circuits really doesn't like solder either and is a chief suspect if one half the output signal is distorted or missing.

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If any speakers need replacing, just bear in mind that the power amplifier runs into two ohms. Each speaker in the 3 x 10" would be six ohms and the 2 x 12" would be four ohms. Six ohm coils were used by Watkins as well as Burns in the old days, but they're getting hard to find now. Fitting a replacement with a higher impedance will shunt the power into the other speakers and make them work harder. A proper recone is favorite, although replacing the whole lot with eight ohm units would be fine. Maximum output power would be down slightly.

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Layouts below are viewed with the chassis the right way up, looking into the back of the pots.

1. Burns Orbit Three Factory Drawing BE 009 03

This is a clean up of the old drawing already available on the internet. It has some major differences in the Channel One tone switching  arrangement compared to the 3 x 10" described later. The 1amp fuse seems to have been added to the schematic later and is probably fine for instrument use. If testing into a 2 ohm load at full power, the LT current draw is 2.1amps and the ac mains is 460mA.

1. Burns Orbit Three "6303" Schematic

The next one is a bit of a mystery at the moment. Thank you to Jon Free at Black Guitars in Australia for posting photos of some back panels with factory schematic stickers. They're described as a 6303 Amplifier. We weren't sure which model they came from, but I just found the same tone circuit in the 3x10" Orbit Three below with CCL capacitors from 1965 (no serial number, unfortunately). Some of the values are unclear, but the circuit for Channel One in particular is a lot different to the BE 009 03 version.

Jon's site's got some very interesting Burns archives. Well worth a look.

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BLACK GUITARS

347 BELGRAVE-GEMBROOK ROAD, EMERALD, VICTORIA 3782, AUSTRALIA

www.blackguitars.com

3.  Burns Orbit Three Schematic Type 882 3 x 10"

The rest of the details and layouts come from the wreckage of a real amp and you can see straight away that the wiring around the mains voltage selector switch is different (and still @#!!£* dangerous if you don't pay attention).

There's no fuse and it's ridiculously easy to flick over to 115V by mistake. Whoever built them also managed to find three core mains wire with two browns and a green. It's just pot luck which wire's the line.

The layout drawings are specific to this chassis.

4.  Burns Orbit Three Power Supply Layout

5.  Burns Orbit Three Power Amplifier Layout

6.  Burns Orbit Three Channel One Layout

7.  Burns Orbit Three Channel Two Layout

8.  Burns Orbit Three Vibrato Section Layout

9.  Burns Orbit Three Reverb Section Layout