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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: 44
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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]
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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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#8 User is offline   Gaolee 

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Posted 15 May 2018 - 02:05 PM

View Postdkevin, on 09 October 2017 - 06:38 PM, said:


That chassis looks like my BR-9's chassis, except that I think the paint is black on mine. The enclosure is a bit like a cathedral radio, with a rounded top and light cream vinyl. I doubt it's tolex. It would be interesting to know whether later BR-9s used field coil speakers or if they had an output transformer and used speakers with a permanent magnet. Mine has a field coil speaker. It's not all that powerful, but it has a clean tone that is just on the edge of breakup when cranked up. It doesn't sound at all like any other amp, and loves P-90s, appropriately enough.
Thump to live.
Live to thump.
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#9 User is offline   Vermonter 

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Posted 05 August 2018 - 06:40 PM

View PostGaolee, on 15 May 2018 - 02:05 PM, said:

That chassis looks like my BR-9's chassis, except that I think the paint is black on mine. The enclosure is a bit like a cathedral radio, with a rounded top and light cream vinyl. I doubt it's tolex. It would be interesting to know whether later BR-9s used field coil speakers or if they had an output transformer and used speakers with a permanent magnet. Mine has a field coil speaker. It's not all that powerful, but it has a clean tone that is just on the edge of breakup when cranked up. It doesn't sound at all like any other amp, and loves P-90s, appropriately enough.


This is my first post, other than my intro post. I bought a BR-9 at a what not shop a couple months ago and brought it to the guy who works on my amps. He got it going, but he said it actually has a GA-9 circuit. Anyone have any idea why that would be? Thanks!!
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#10 User is offline   dkevin 

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Posted 06 August 2018 - 09:47 AM

I am not privy to the logic behind Gibson's amp manufacture. I can only look at the evidence of the amps in existence and guess what they did and perhaps why they did it. There are several amps in the Gibson line that are, in fact, exactly the same although they have different model numbers and sport very different aesthetics. If I had to hazard a guess why Gibson did this I suppose it might have something to do with the ever-changing amp lines. There is (as has been previously mentioned) an early BR-9 which uses a 6SN7 preamp tube- is push pull in design- and utilizes a transformer to invert the phase to drive the output tubes. In my experience, this amp is rather rare, even though its outward appearance is identical to other versions. There is a second version, like yours, that uses a 6SJ7 for the preamp and is single-ended, parallel-output in design...this chassis is also used in the GA-9 and early Gibsonette which are very different in appearance. Why would Gibson design several different amp models with very different appearances using the exact same chassis, you ask??? I think it had something to do with the move from octal preamps to more modern noval preamps. In each of these examples, the cabinets changed as well as the speakers. The BR series amps used an 8" field coil in the trapezoidal cabinets and a 10" field coil in the later G-medallion larger cabinets. The GA-9 used a linen covered cabinet and a 10" field coil. At any rate, when we reach the early 50's, the preamps begin to move toward the noval design. The outer coverings change from linen to light brown to buffalo grain and finally to tweed at the end of the fifties. I think the decision to use the exact same amp in several different amp models was driven by their desire to use up the stock they had on hand and look to the future development of the smaller 9 pin preamp. I have a GA-25 amp chassis from the late 40's that is a hybrid of the GA-25 schematic and the early 50's issued GA-30 amplifier. It appears to be a GA-25 that was made in the interval between models and incorporated several of the features of the GA-25 along with features from the GA-30. If you follow Gibson's amplifier history much at all, you will become aware of the frequent undocumented changes. As if this were not enough, you can add in the numerous owner/user mods done to convert their "Practice-size" amp into a "Marshall-wanna be" and buying a Gibson amp becomes a bit of a moving target. Nothing can be taken for granted and each change in the model line (name or number) can drastically alter the design of the amp. But all of these concerns do not make me run away screaming from Gibson guitar amps. The payoff is too satisfying! But, let the buyer beware....do your homework!
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#11 User is offline   Vermonter 

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Posted 06 August 2018 - 04:57 PM

Wow... so much information. Thanks so much. This amp was all original. The tube amp guy said it hadnít been touched. I learned more about Gibson amps from your post than through hours of online research. Iíll discuss this with him and see what he thinks. Thanks again!!
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