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Gibson Amplifiers (24 posts)
01-February 12
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User is offline Oct 12 2017 06:28 PM

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  1. Gibson BR-9 chassis

    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).
  2. GA-77 amp

    03 July 2017 - 10:21 PM

    I found a Gibson GA-77 amp chassis ...actually I got it on Ebay and also managed to get the cabinet it was paired with. The cabinet is not the tall, buffalo grained cab with a "77" on the front. It is more akin to the later version GA-77 called a Vanguard amp. However, this cabinet is a dead ringer for a Fender Pro amp circa 1959 or so. The side walls are thin and the top and bottom front panels are 2 1/2 to 3" wide. The tolex is a black/white sort of pattern that I have never seen on a Gibson amp before. The chassis is an early version (pre-Vanguard) with 7 tubes and 5 controls. I am wondering if any of you have ever seen a Gibson amp with a cabinet that looks like this. The cab is not constructed with finger-joints as the later amps are. This one more closely resembles the GA-25 or GA-20 with overlapping cuts. (Sorry..I forgot the technical term) I believe this version of the 77 was made from 1954-1957. In 1958 I think the amps were redesigned to use 6 tubes and 6 pots.
  3. Clavioline/GA-40 amp

    24 December 2016 - 04:08 PM

    I recently got a Gibson Clavioline amp. It was designed to amplify a keyboard. When I got it, I was surprised in several ways. The chassis mounts inside the cabinet with only the pilot lamp and off/on switch protruding through the top of the cab. There are no pots in the amp as designed. It uses a 6J5, two 6V6's and a 5Y3. The cabinet is pretty big. The chassis is long but shallow (nothing like the GA-40 I have). At first I thought I might build a tweed Discoverer...GA-8 because I really like the sound of that amp. However, as I examined the components I realized this amp uses the same power transformer as the GA-40 Les Paul amp. Now I am thinking that it would be a shame to use that huge PT to power a GA-8. I am now leaning toward a GA-40 mid-late 50's amp. The cabinet has plenty of room for a 12 inch speaker. I will have to think creatively to come up with a way to mount volume/tone/tremolo speed and /tremolo intensity pots. If I do go for a GA-40, the new tube array will be 5879's...6SQ7...12AX7...2 ea. 6V6's (push-pull) and a 5Y3.



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