Gibson GA 40 T - Les Paul Amp - repair, overview and sound demo
Вставка
- Опубліковано 16 вер 2024
- This amp came into the shop with a few problems: channel one was dead, tremolo didn’t work, a good amount of background noise and motorboating. See how all these issues get fixed and hear the result: a warm sounding amp with a nice breakup and a deep and rich tremolo. In fact, there are fantastic amps besides Fenders and Marshalls!!!
And here is another Gibson made amp from this era: • Made by Gibson: EPIPHO...
Excellent Tremelo sound! Freddie King led me here.
In my humble opinion, after 61 years of guitar playing, I am thinking that these old Gibson amps faithfully and accurately amplify the acoustic tones of Gibson's hollow and semi-hollow body guitars. This amp sounds WONDERFUL!!
Yepp!
The inside looked better than the outside, the stuff that counts looked original - sweet amp! Love my 1958 GA-40 and P12P speaker (RIP).
Its such a treat to see these old beauties ending up in the hands of those that care.
Thanks a lot! In fact, it’s a privilege to work on these old beauties and bring them back to life.
Info for newbies: the 5879 pentode preamp is a bit like the EF86 (AKA 6267 OR Z729) used in some older Vox amps, but with lower gain and a different pinout (so not directly substitutable). Here in the States, the 5879 was used as a mic preamp in some commercial PA/paging amps of the type used in schools, warehouses, and so on. As for the 6SQ7, they were frequently found in radios where the diodes were used in the detector and discriminator circuits , but in this guitar amp only the triode section is being used.
Stunning sound
Wow. Dirty and butchered. Great job bringing it back -- sounds nice and swampy with the trem engaged.
Good work. You gave it new life, and it sounds great.
You make good videos.
Sounds great!
It sure sounds nice now that it's fixed. It'll probably work great with any guitar you plug into it.
Filtertrons, gold foils, lipstick tubes, and those chrome De Armonds on the Silvertones and Airlines ought to sound great.
You are absolutely right! It sound gorgeous even with my good old Telecaster! These guys knew what they were doing, when they designed amps.
@@martinstubeampworkbench2299 I've got a Princeton and a Tremolux, both Tweeds. The Tele is my favorite with both of them, and I swear I can get any amount of headroom I want, and I can put the "edge of breakup" at any volume level I like.
The whole thing is totally controllable by the pressure of my right hand.
That's what tubes are all about.
Pedals? What pedals?
@@jpalberthoward9
Yes sir! I agree! A Telecaster beats them all . The bridgepickup and the tone pot is all you need to get any sound you want. Pedals? Nono!!
@@martinstubeampworkbench2299 Have you ever listened to the interview with Steve Cropper? He said he used to have about 20 guitars, and he dragged them around with him to every session, but the producers invariably said "Steve, break out the Tele, it sounds the best!" So he sold all the other ones. He said that Teles sit in the mix better than anything else, and the clarity you get from them makes them cut through when they need to.
The combination of a Telecaster and a Tweed amp is like peanut butter and jelly, or beer and pizza, or jeans and a T shirt.
A complete and total natural perfect match.
This amp came into the shop with a few problems: channel one was dead, tremolo didn’t work, a good amount of background noise and motorboating. See how all these issues get fixed and hear the result: a warm sounding amp with a nice breakup and a deep and rich tremolo. In fact, there are fantastic amps besides Fenders and Marshalls!!!
Nice playing through a great (!) sounding amp...
What was your test guitar/pickup used?
Thanx for a great vid
This time I was playing a homemade Telecaster with a Mahagoni body equipped with Tonerider PU. Actually it’s the guitar you can see (and hear ) in the openings of my videos.
MARTIN, can you show the formula and calculations to get the biasing voltage based from the power tube dissipation wattage? It's like a reverse formula to take the tube dissipation wattage and calculate the bias voltage on various amplifiers
Mmmmmmh….. this Gibson amp is cathode biased. In my oppinion it makes no sense to calculate „backwards“. Here is why: different tubes have different current draw, even if there are the same type, brand etc. Tubes are individuals. Output Transformers have different resistenses, cathode resisters vary as well. So, to get a precise outcome, it’s better to know all these values. But there is a very helpful bias calculator on robrobinette.com. Check that out. Greetings
Does this have the baxendal tone stack? I have the G45 maestro version with separate bass and treble. Tested the resistors but haven’t gotten to the tone caps on the back side. Neither bass or treble have any effect on tone. Regardless, this amp smokes in tone. Love it….just want to be able to tweak the sounds available in this amp. Do you think the solid redwood contributes to the sound? So unique. It had been re-tolexed with crap -brown. Thinking of stripping it down and letting the wood speak for itself.
Hi there
No, this version of the GA 40 has no tonestack at all, just a single knob to bleed of high frequencies . Simple, but all you need to dial in the sound. This simple solution was used on almost every Valco amp from the 50th and on the famous 5E3 Fender Tweed Deluxe. I never had a G45 Maestro in the shop, so I can’t tell, what kind of toneshaping Gibson did there.
And yes, I think a solid wood cabinet does matter. It acts like an acoustic guitar, it resonates. Chipboard or Plywood doesn’t. And solid wood is in comparison to chipboard lightweight.
Greetings
Did you top mount some those of those coupling caps on the board that were mounted on the back of of the turret board? I have a GA-45 which is nearly identical except for the input resistors and a separate bass and treble control(currently has no effect on tone shaping). Checked my resistors and they were all in good shape. Is a single tone control a better tone shaper? Thanks for the video.
Yes, I did . Coupling caps , bypass caps and the lfo caps for the tremolo. I didn’t change the tone caps , they stayed behind the bord. Normally they won’t fail, because they never see any high voltage. But if your treble control don’t work, maybe you should check them.
@@martinstubeampworkbench2299 Neither bass nor treble are barely audible whether they are at 0 or 10. I’m playing through an old Magnavox large alnico speaker comparable (exact same as I understand) to a Jensen P12Q. Gave me a bit more headroom which this amp needed as I had been running a 60’s rola 15 watt alnico. Unfortunately the gold Jensen 4 x 8” speakers were gone long ago. It would get rowdy at 3-4 on the volume pot before I swapped to the P12Q. Glorious sounding amp… just would like a bit more flexibility to eq different guitars. I imagine it was a perfect match for the P-90’s of their day. I dread pulling that board. Has those old white Cornell Dubilier oil caps from what little I could see on the back of the turret board. Thank you as I think this is the only vid that I’ve seen posted of maintenance on this amp. Almost a dead ringer for the G-40.
Well, in some of these old amps, the tone circuit is not very efficient. But when there is almost no audible change , there is definitely something wrong.
how come I never see any of these techs discharge the caps? I am a newby, and I have a fear of electrolytic caps......and also, does this model have a death cap?
Discharging the caps is a must! But it’s only a 15 minute video and I have to decide what to show, because a repair takes hours. I’m shure, every amptech discharges or at least checks the voltage before sticking his fingers into the circuit. The Gibson had a deathcap, but with the three prong cord I installed it’s obsolete anyhow. I removed it.
Thanks for your interest!
@@martinstubeampworkbench2299 thanks for replying.