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Gibson BR-9 chassis

#1 User is offline   dkevin 

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Posted 20 September 2017 - 02:16 PM

I have been on a quest to find an early BR-9 amp to rebuild. Just the other day I was looking on the Bay and found a chassis with tubes in mostly original condition for $70 . Couldn't get my wallet out of my pocket fast enough! This particular amp appealed to me because it was exactly as the commonly available BR-9 schematic described. Most of these amps I have encountered have the 6SJ7 preamp tube and are single-ended, parallel output amps. Don't get me wrong! These are still great amps! But I always wondered what the original design sounded like and how it differed from the later variant. The amp showed up today and I tested the tubes. The 5Y3 was dead (probably due to the ancient paper-tube electrolytic caps). The 6V6GT's were strong. The 6SN7 tube socket had a 6X5WGT rectifier installed in the preamp position. Bet it had difficulty making sound! The 6X5 will go in my stock for several old Silvertone amps. I have 6SN7's and spare 5Y3's. The fuse holder was sheared off. I clipped the wires to the PT and tested it. It read; 391vac to the 5Y3 plates...5.5vac to the 5y3 heaters and 6.9vac to the preamp/output tube heaters. The interstage transformer (PI) tests out at 546ohms. I am hoping to be able to use it. As it stands, I need to replace the E-caps, wax-paper capacitors, power cord , output transformer and add a choke so I can use a permanent magnet speaker. The caps and such, I already have on hand. The transformers I will have to order. They should come to $70 (not including shipping).
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#2 User is offline   dkevin 

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Posted 20 September 2017 - 05:14 PM

Attached File  Gibson_BR-9.pdf (61.01K)
Number of downloads: 25
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#3 User is offline   badbluesplayer 

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Posted 22 September 2017 - 03:30 PM

Sounds like a fun project. [thumbup]
_________________________________

TENNESSEE AMPLIFIER COMPANY
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#4 User is offline   dkevin 

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Posted 23 September 2017 - 04:27 PM

I have another BR9 chassis that I rebuilt too. It was a 6SJ7 preamp BR9. I installed a choke and OT but chose an Allen amps TO-11 because that design is single-ended, parallel output. It also was fun to do and sounds very good! In this amp, I have replaced the cracked A/C cord and the large cardboard Capacitor. I used 22uf/10uf/10uf mounted on terminal strips with required dropping resistors mounted in between them. I chose to distribute the power on the terminal strip as opposed to the factory method of mounting the resistors on the unused pins of the 2nd 6V6. I ordered a (Princeton size) OT and a 50MA choke (Deluxe size) from Amplified Parts. Of course they announced a flash sale (-15%) the day after I placed my order. Oh well! By the time the transformers get here I should be able to replace all the wax-paper caps and the few resistors I need.
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#5 User is offline   Tyler A 

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Posted 08 October 2017 - 08:23 AM

You are going to have a nice collection of oldmgibson amps if you keep this up!
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#6 User is offline   dkevin 

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Posted 09 October 2017 - 07:11 AM

Believe it or not, my goal wasn't to collect amps. I really enjoy learning about the different models and in order to do so, I had to have an example in hand. Most of the amps I have are not pristine, collector grade examples. They have nicks and tears in the coverings, gouges in the cabinets, rust on the chassis faces and other cosmetic shortcomings that make them undesirable to a collector. When I was beginning I sought out Gibson amps because that was the maker of an amp I borrowed for a gig from a friend and I loved the tone and vibrato/reverb. It turns out, they were not (at the time) in high demand so the price was reasonable for a fixer. As long as the transformers were good, all the other components were readily available to restore the amp. I seem to hear a lot of complaining about the layout of Gibson amps Granted, they are not as neat as the Fender style of mounting most of the components on a fiber board. But if you take your time, trace the physical layout and compare it to an appropriate schematic, you can see where all the parts are and they are easily removed and replaced. Lately it seems I have gotten my hands on chassis only BR series amps. They are some of the earliest Gibson amps. Most have field-coil speakers. But the chassis only amps can be adapted to run as a head with an external speaker , and they sound good! I think I've paid less than $100 for each of the BR chassis' I have.
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#7 User is offline   dkevin 

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Posted 09 October 2017 - 06:38 PM

https://imgur.com/a/Datre
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