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1947 Gibson BR-6 Amp restoraton


FarmerTed

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I recently purchased a vintage tube amp, listed as a 1947 Gibson BR-6, and has 2 inputs, not 3 like seen on the BR-6F version. It is only the complete chassis, without a cabinet or speaker. Tubes were included.

After extensive research, this chassis has baffled me. Most odd, is that the amp has both a power transformer, and a 25 watt output transformer mounted on the chassis. Both transformers are vintage, built by Sencor in Chicago.

Every photo of the BR-6 I have seen only shows a power transformer on the chassis, with an OT choke mounted on the field coil speaker.

 

This leads me to believe that this chassis can be connected to a full range speaker (one with a magnet, not a field coil). Am I correct? Or am I missing something?

 

While most of the components appear to be original, the previous owner had replaced the three original .05uF caps with Orange Drop style caps, and the 20uF caps replaced with modern low-budget axial caps.

 

I replaced the old 2 prong cord with a quality 3 prong, with the ground to chassis. Next is to take it to my local technician for a full test and analysis of the tubes, transformers, caps & resistors to see what needs to be addressed.

 

ANyways, I am looking for insight about the transformers I mentioned. Anyone?

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  • 2 months later...

I recently purchased a vintage tube amp, listed as a 1947 Gibson BR-6, and has 2 inputs, not 3 like seen on the BR-6F version. It is only the complete chassis, without a cabinet or speaker. Tubes were included.

After extensive research, this chassis has baffled me. Most odd, is that the amp has both a power transformer, and a 25 watt output transformer mounted on the chassis. Both transformers are vintage, built by Sencor in Chicago.

Every photo of the BR-6 I have seen only shows a power transformer on the chassis, with an OT choke mounted on the field coil speaker.

 

This leads me to believe that this chassis can be connected to a full range speaker (one with a magnet, not a field coil). Am I correct? Or am I missing something?

 

While most of the components appear to be original, the previous owner had replaced the three original .05uF caps with Orange Drop style caps, and the 20uF caps replaced with modern low-budget axial caps.

 

I replaced the old 2 prong cord with a quality 3 prong, with the ground to chassis. Next is to take it to my local technician for a full test and analysis of the tubes, transformers, caps & resistors to see what needs to be addressed.

 

ANyways, I am looking for insight about the transformers I mentioned. Anyone?

 

When you're converting the plug from 2 prong to 3 prong, you may need to reconfigure the wiring a little. The hot (black) should come into the amp and go to the fuse and then the switch and then on to the power transformer. The fuse should not remain on the white wire.

 

As far as the transformers go, the output transformer will hook up to the speaker, but there should be a choke or maybe just a resistor between the output transformer and the rectifier tube in order to drop the voltage. Trace the wires back from the OT toward the rectifier and see what's in there. Go from there.

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