Need help finding output transformer for Gibson BR-1 amp.

[valcotone]

hi guys, I have a 1946 BR-1 with original OT and 12" Jensen field-coil speaker. I think it's a wonderful idea to bring your amps back to life. Ideally, you'd find an original field-coil Jensen with the OT attached... but what are the chances?

My suggestion would be to find a suitable speaker and output transformer. I think something like a Tweed Pro repro OT would be fine, and an AlNiCo 12" like a P12Q or P12N would be a good match as a speaker.

Then replace the field-coil with either a choke or wire-wound resistor. If you can find a choke with a similar dc-resistance and inductance as the original field-coil you're set, but I'm not sure how to get the correct specs. Again, a 5E5-A Tweed Pro repro choke might suffice.

Here's a clip of my BR-1 with a Guild CE-100DP Capri.

Good luck!

[Gibson BR1]

Speaker

Hi, I feel that it would not be so difficult to find an original Field Coil Jensen. I will try to find time to measure the DC resistance of mine so DrDanke can match it up. Is DrDanke still following this thread?

[streamofstudio]

Hey guys,

I am also restoring a BR-1 though I am lucky - it only really needs a new surround! I have used this beauty on a handful of recordings and even with the flapping surround, at lower volume, low-cut frequencies is one of the best tones I have ever heard. I don't have much to add yet but will try to take note of any variations from schematic, which I am sure I will find.

The story of this amp is funny - it was sitting in an outdoor shed for 30+ years and given to my father by a coworker. Worked on first try and still does minus the surround issues. The AC chord is actually stiff and crumbling from the conditions it endured. So obviously that will finally be replaced as well as well as electrolytics. How's everyone's restores going so far? Thanks for all the inevitably helpful info as well! -Dan

[Gibson BR1]

Hi Streamofstudio, I would really appreciate knowing if the panel that the speaker is mounted on has a slot cut out like the one on the back (about 2"X10").
I must recover mine and cannot find tolex like the original. The closest thing I have found is real leather. I am uncertain about trying to use leather.

[enzo5000]

I recently was able to find a BR-1 in excellent condition on Craigslist of all places! I was lucky enough not to pay a fortune for it. I've gone through it, had to change the two 6SC7 tubes to Haltron NOS 6SC7GT tubes because the old metal cans were slightly microphonic. Everything else checked out well, seems in good shape and sounds amazing.

[valcotone]

Man, it looks in such fantastic condition, maybe the best one I've seen.

Thanks for sharing the pics Enzo!

How would you describe the sound?

[enzo5000]

Wow...how do you describe sound? It's a little dark and smokey sounding. The 12" field coil speaker really has a large open feel with more head room than you'd think for a single speaker cab. I play it though the Instrument Channel mostly and add a little gain and reverb with pedals. The Mic Channel is a little buzzy for my taste, but it is one loud amp in either channel I can't use it above 4 without the neighbors complaining! I've been playing a Telecaster with TV Jones pick ups through it and the combo of the twangy chime of the those pick ups and the "brown sound" of the amp balance out really nicely.

[luthierwnc]

I'm piggybacking on this older thread because it is close to a project I'm considering. I have a chassis that I'd like to build into a BR-1. I got to recap one maybe 15-20 years ago and really enjoyed the sound. In a ground-up design I'm a little less thrilled with using a field-coil speaker. The PT is around 550VCT and drove a quad of 6BQ5s so the volts should be about right if I use an LC filter. It also gets rid of that 20k bleed resistor coming off B+2. I have a nice P12N that should fill the bill tonally. It will need a new OT and choke.

What I'm not sure about is whether there is some sonic mojo I'm leaving behind and if there are techniques for replicating the field-coil experience more accurately. Any comments or ideas would be welcome.

Thanks, as always, Skip