Gibson BR-9 / GA-9 Hybrid Vintage Guitar Amplifier ca 1955

[@UncleDoug]

Again, thanks for your kind words. It's nice to have a forum like KZbin to present information and discuss puzzling inconsistencies in these great old amps. I was indeed fortunate, in this case, that the original owner's pamphlet and schematic were left in the cabinet. Too bad that doesn't happen more often...:)

[@UncleDoug]

That's great news, BBus. It is indeed a very interesting little amp and it looks like it finally found a good home. Congratulations on your successful repair and best of luck with future projects......

[@UncleDoug]

Thanks, Dave. It's all a bit confusing, since there are three different schematics that relate to this chassis. Using the numbering system from the GA-9, the values in the BR-9 owner's manual schematic (and my amp) are: C1 is 20uf, C2 is 0.1uf (instead of .05uf), C3 is 0.05 uf. I hope this helps.

[@UncleDoug]

Yes, that sounds right to me. I would hook all this up with jumpers on the bench to be sure it works OK before installing everything. The output transformer can be attached to the new PM speaker for a more "original" appearance or perhaps hidden under the chassis if there is room. You're also right about the resistor being the tubular, wire-wound type, spaced away from any wood (heat). I used this modification on jukebox speakers when the FC's failed. Good luck !!

[@UncleDoug]

Great, BBus. I believe you are correct about the very minor difference between the two schematics. Good luck with your repairs.

[@pearsonart]

Have one. Love it. Thanks so much for covering it.

[@UncleDoug]

You're welcome, PA.

[@UncleDoug]

Yes, the cathode (5) and screen (3) are connected in the original schematic. If the voice coil had failed, you would probably get no sound at all. There may be a short in the field coil. Measure its resistance (should be 1000 ohms), and when the speaker is energized, see if the field is strongly magnetic (i.e. attracts a steel object). If it's bad, substitute a 1000 ohm 50 to 100 watt resistor for the field and use a permanent magnet speaker.

[@UncleDoug]

There may be a short in the field coil winding that prevents the formation of a magnetic field to drive the voice coil. This would be like a permanent magnet speaker with almost no magnet. Regardless, it's easy to fix. Connect the two leads that normally go to the field coil to a 1000 ohm resistor of high wattage (at least 50W....it will get hot) and then connect the voice coil leads to a proper impedance PM speaker that you have installed in the cabinet. It should work well.

[@nros5020]

Hi uncle doug, currently going down this rabbit hole in regards to field coil magnet speaker swap for PM speaker, I have read conflicting things in regards to just put a resistor inline vs a resistor as well as a choke. I know a decade has passed since your comment on here, are you still of the mindset no choke is needed just a resistor? Any help greatly appreciated! Cheers -Johnny

[@UncleDoug]

I have successfully substituted a Fender filter choke for the field coil with no other alterations, Johnny.@@nros5020

[@lostmypuzzlepiece]

So as luck would have it. I purchased a BR-9 that has the smaller trapezoidal plexi-faced grille as the one pictured in the buyer’s guide. However, I have the 6SJ7 version of the chassis with the 6V6 directly behind it. No shield. There appears to be no schematic that matches this on the web, or at least not where I could find it. Your owner’s manual is the only one I’ve been able to locate. I snagged a fairly decent screen capture of it. Hopefully that will help me navigate this very neglected amplifier back to a studio beast. Thanks, Uncle Doug!

[@UncleDoug]

You're welcome, Adam. I'm glad the video was helpful. There certainly are a lot of variations of this model and circuit.

[@dyeeb]

Hey Uncle Doug - You just answered a question I've had for over 30 years. I bought this "BR-9" at a pawn shop for $20 in 1989. It didn't work because....drumroll...the tubes were in the wrong sockets. I straightened that out, but could never figure out why it didn't appear to be a straight-up BR9. It has the 6SJ7 preamp tube and NO SERIAL NUMBER. The speaker is a "F10U" and reads "220326". It's a quiet amp, and I love it. It matches my '57 Silvertone archtop nicely. Thanks for the info!

[@UncleDoug]

You're welcome, Dan. It seems that Gibson experimented a lot during that period of time and many different hybrids were produced.

[@krisom4356]

Uncle Doug... I just received a BR-9 / GA-9 mutant tthat looks just like the one in your video. I has a 1953 Jensen 10" field coil speaker, no PI transformer, and uses 6SJ7 and 2 6V6GT operating in parallel as Single Ended mode. I think it could be as late as 1955 based on some of the other components and it sounds great. Tubes are in same position as your video also. thanks for all your information and for helping in my decision to get this unique amp.

[@UncleDoug]

Congratulations on your new acquisition, KR. These hybrids are unusual amps that do indeed sound great. You're welcome for the info :)

[@bastardbus]

Thanks UD. I opened her up and worked on her tonight. It was "supposedly" serviced (what a JOKE!) A $1 walmart cord and 3 new filter caps. I replaced all the old original paper and e-lytic bypass caps which where all leaking. Resistors where all within specs and tubes good. I fired her up and WOW...that is what I was originally expecting. She sounds GREAT and what an interesting sounding amp with the parallel 6V6s and field coil. I really like this amp now. Thanks for the video and help.

[@DaveHilts]

Okay, so what I can find is a 100 watt 1K wire would resistor and I should then connect it between the 20mfd and 10mfd caps (not too close) to take care of the field coil load, then install a 8 ohm PM speaker and either mount the existing OT to the speaker or somewhere inside the cab and wire it back up to the speaker. Does this sound like what you had in mind? Thanks for the help. Dave

[@billroberts849]

I recently took one of these in on repair. Exactly the same but from 1952 BR-9 Chassis with GA-9 wiring. Some small differences in the Power transformer being a 271Z25 rather than the one on yours a 271X25 that they used in '55. The Z mounting horizontally instead of vertically. The C2 was a .01 cap instead of the .05 shown in the schematic as well as the 200 ohm 7 watt resistor was 150 ohm. I would be curious to know if yours had the 200 or 150 ohm resistor? Maybe the 150 is not original? To bad you did not give us a look at what was in the chassis. The real disappointment for me though was after spending a significant amount of time in restoration only to find both the Power transformer to be toast as well as the field coil open on the speaker.

[@UncleDoug]

I have enjoyed several similar grim discoveries, Bill, in which the really bad news comes just when you think you're nearing completion :(

[@oldguy5381]

You’ve gotten better but the old stuff is fun as well.

[@UncleDoug]

Thanks, OG.

[@EGM210]

Great looking amp. I have the BR-9 amplifier. The chassis is the same as yours but mine has the other cabinet. I was told the BR-9 was 1953. ??

[@UncleDoug]

Thanks, EGM. According to the VG Price Guide, the BR-9 was offered from 1948-1954.

[@DaveHilts]

thanks Uncle Doug! I also think that I need to tie pins 3 and 5 together on the preamp tube 6SJ7. My Jensen speaker has very low output so I think its a gonner. Its ID code is 200 321 so it a 1953 model year. I can connect a 8 ohm speaker to it with aligator clips and get good volume so I think the speaker coil has failed. That is a bummer because I'm not sure how to proceed with a speaker replacement because of the field coil. Thanks for the info! Dave

[@nros5020]

Have this identical amp, did you ever have any luck in swapping out field coil speaker for more modern speaker?

[@DaveHilts]

Hey Uncle Doug! I have one of these amps and am curious as to the value of the caps on the preamp tube. The schematic for the GA9 shows both C2 & C3 to be .05mfd caps. Is this what your schematic shows?? Thanks and great video! Dave

[@DaveHilts]

The field coil measures 870 ohms but when the amp is on the field coil feels warm to the touch but is not magnetic. I can take aligator clips and tie to the OT leads on the speaker and get loud volume out of an 8 ohm permanent magnet speaker.

[@peterhutchinson3424]

Hello, is their any chance I could get a copy of the manual you found inside. I just picked one of these up and it is exactly as you describe the one you have.

[@UncleDoug]

Sorry, Peter, I have no scanner to make a copy. Other than the schematic, it's not much help.

[@bastardbus]

Hi UD, don't worry about emailing me the schematic. I found the GA9 online...copied it and compared to the one in your video. The only difference I saw was C2 .05 compared to what looks like ,1 on yours.

[@SiliconSet]

Great video! Many thanks!

[@UncleDoug]

+SiliconSet You're welcome, SS :)

[@michaeldeangelis9202]

Thanks Uncle Doug. I inherited my father-in-law's gear which includes the same amp in your video and a Fender Duo Sonic electric guitar from the 50s. I always wanted to know the history of the amp. At higher volumes the amp has a noticeable hum. Is there a reason for that?

[@UncleDoug]

You're welcome, Michael. It depends on the frequency of the hum. 120Hz indicates failing filter capacitors. 60Hz can be due to literally hundreds of different causes. Regardless, any noticeable hum is a sign of some internal problems.

[@michaeldeangelis1225]

@@UncleDoug Hey Uncle Doug....I finally got my interim BR-9 amp repaired. I know it's been a year since I last contacted you but everything in good time. I found a guy in my town who repairs amps and you were right about the capacitors. He replaced the capacitors and the power cord which was badly deteriorated and the amp sounds great. No more hum. He did note that the transformer does not appear to be the original Gibson. There is a Hammond transformer instead. Thanks again for your video.

[@danielthomas3057]

I find it odd that they physically placed the 6V6 tubes so far apart considering they are connected in parallel. Overall this amp was an interesting twist indeed.

[@crbielert]

I just managed to snag one of these hybrid models on eBay :). Can't wait to get it in the mail, get it all sorted out.

[@UncleDoug]

Congratulations on a great acquisition, CR. I hope it exceeds your expectations.

[@crbielert]

Thanks! Me too. A previous owner decided to repaint the chassis silver I'm hoping that it's a cheap spray paint that I will be able to strip off and not damage the brown underneath. Exterior cabinet looks great though.

[@UncleDoug]

Don't you wonder what possesses people to spray paint amps and guitars......especially silver :>(~ I posted a video years ago about a BF PR that was completely painted flat black.....why.....why.....I ask ????

[@crbielert]

Yeah, it just boggles the mind.

[@bastardbus]

I was wondering if it would be possible for you to post or email me a copy of that schematic. I just picked up a BR9 in the trapezoid case but it has the odd ball 6sj7 parallel 6V6 chassis like yours. It is running weak and needs gone through. Thanks T

[@amoruzz]

That was a very clean chassis. I had one just like it back in 96 along with the lap steel and foolishly sold the set to a collector for cheap. : (

[@UncleDoug]

At least you made the collector happy, Amo :)

[@serpentstudios7768]

Wow what parts have u built to this cool BR-9?

[@UncleDoug]

Greetings, Sam. This amp is completely original, just like when it left the Gibson factory.

[@vhm14u2c]

Looks like the reason 6v6 on the left side of chassis was to permit speaker clearance.

[@UncleDoug]

It could well be, Vince.

[@moodyga40]

so uncle Doug when 2 6v6 are in parallel the wattage is increased and the bias current is increased as well

[@UncleDoug]

+ian “valve doctor” forster Yes, in parallel, the output wattage is increased a bit, but not as much as it would be if the tubes were in a push-pull relationship, and the plate current, as measured by voltage drop across a common cathode bias resistor will appear to be double since it is the current through both output tubes.

[@moodyga40]

goin to build this cab for my amp www.vintagehofner.co.uk/britamps/watkins/dominator/dom22a.jpg

[@UncleDoug]

Wow....what a beautiful design. Let us know how it turns out.

[@moodyga40]

i have worked out the cabinet changed it a bit as not to get done for copyright how should i cover it in tolex

[@UncleDoug]

That's not something that can be answered in a few sentences, Ian. I suggest that you study the problem and come up with a solution. I'm sure you'll find a good way to do it.

[@timothyb1559]

LOL!! 🙃 Gibson has been giving us ampheads nightmares for over 65 years.

[@UncleDoug]

Both via their schematics and the tone of their mid-60's amps.

[@UncleDoug]

If you send me an e-mail address by message (not comment.....to preserve your privacy) I will send you a digital image of the original schematic.

[@lostmypuzzlepiece]

Don’t suppose you still have this file. I have the same ga-9 circuit in my br-9, but would like a correct copy for my records.

[@SuperCarver2011]

Gibson amps were not too bad. Too bad that their later efforts in the 60s were discontinued because they decided they couldn't compete with Leo's products. Gibson's cabinet styling sucked compared to Fender. That left a big void for Jim Marshall to step in and the rest is history. I got the book on Gibson and those early amps were made for Gibson by it's parent company (CMI Chicago "Chicago Musical Instruments' I believe), while the later amps were designed by Seth Lover (father of the humbucking pickup) and Walter Fuller "inhouse" and production was done then in Kalamazoo Mi, once the Electronics Dept was formed after invention and production of their famous humbucking pickups. This may also explain the changes that took place back in those days. More The design philopsophy between the Fender amps and Gibson amps was polar opposites as far as the "sound' and The Fenders won out as being the most popular with most bands of the day, except for C&W which liked the more mellow sounds of the GA series amps. Don't know how much influence Les Paul had on the GA amps, but he was still somewhat active until Ted McCarty (CEO) left Gibson in 1966 when he bought Bigsby.

[@guylester8763]

I have this same amp… first I have found as to what it is!!!

[@UncleDoug]

Apparently they are not particularly rare, since several other viewers said the same thing.

[@gregghubble9550]

Just picked up one

[@UncleDoug]

You're a lucky guy, Gregg. I think you'll find it to be a really nice amp.

[@snarfusmaximus]

I have an amp like this - a BR-9 with the GA-9 circuit but it has a 6" field coil speaker. When I received it, it must have been stored for many years as the power cord crumbled to bits after I unravelled it. Everything inside was original. I replaced the old caps, a couple of resistors that had driifted in value by a fair amount and put in a proper earthed power cord. Sounds lovely. www.flickr.com/photos/35799859@N00/sets/72157629663950056

[@UncleDoug]

snarfusmaximus Nice job and very well photographed, SM. There are interesting differences between the GA and BR versions: Your output configuration is push-pull, while mine is parallel, and your speaker is 6" while mine is 10". You would think the larger speaker would be better suited to the higher P-P output. Thank you for sharing this with us.

[@snarfusmaximus]

Uncle Doug My amp is definitely has the 6V6's in parallel. Check out the schematic on the page I linked - the plates on the 6V6 tubes are tied together. Funnily enough, although there is more output power, the speaker is so innefficient that my 5W tweed champ clone is louder.

[@UncleDoug]

You're right, SN. After I enlarged your schematic, I could see that they are in parallel. Thank heavens for trifocals and magnification :)

[@dhpbear2]

2:10 - That could get mistaken for a sewing machine!

[@UncleDoug]

My mother had a sewing machine in a similar case.

[@whynotme5926]

Very weird but, interesting?

[@UncleDoug]

Indeed :)