1966 Gibson GA20RVT Minuteman Service and Demo
ฝัง
- เผยแพร่เมื่อ 18 ต.ค. 2024
- In this video we'll take a look at the guts of a later model vintage Gibson GA-20RVT amp and talk about what made some Gibsons sound thin and uninspiring in the late 1960s and how to fix that. We will also look at the schematic and discuss how Gibson circuits can vary wildly from published schematics.
I have this same amp that I purchased when I was 16 years old. I re-capped and added a 3-prong plug maybe 10 years ago. It is working pretty good but makes some strange popping noises every now and then. So I'm going to be trying to get this resolved and watched this video in preparation. I realize that maybe part of the mystery of the actual circuitry not matching the schematic may be solved. On the inside of the cabinet of my amp is a full schematic pasted to the side of the cabinet. It is quite different from the one you find if you google for the schematic or the one that Brad was using when doing this restoration. My schematic shows no "tone sucking network" and it indeed shows V4 is a 12Au7, not a 6eu7 as shown on the commonly available schematic. I am pretty confident that when I trace out the components on my amp it will match the schematic pasted inside the cabinet. I ran into this same issue with a GA15rvt that I am working on. There are two schematics for it and they are quite different. So a big part of the bad rap Gibson may have for the actual circuit not following the schematic may in fact just be because there were multiple schematics for the exact same amp but when you google for them you only find one version. I still wonder whether the removal of the tone sucking network was done in later models to fix the bad tone issue, or that network was added to later models in some failed attempt to improve the tone. I took a picture of schematic I have and would be happy to post it somewhere if anyone has any suggestions on where to post it.
Yep. I have this amp too. The schematic inside the cab does not match the one Brad used in the video. Mine also has the 12AU7 in V4 and no "tone sucking networks." Everything in mine is completely original, never been serviced, including the RCA tubes and speaker. But I think it needs new electrolytic caps and a new reverb tank.
Oh my! The Killer tone this amp has is Awesome!!!
Nice work Brad! Another one knocked right outa the park . Beutiful! specially these amps you got the gift my freind!
I just bought one of these. I love it.
I know this is an old video but I am trying to decide between this Gibson and Traynor YGM-3. I will mainly play clean to edge of break-up, with a complete pedalboard. The Ampeg Gemini 1 is a wildcard. What's your take Brad?
Regarding the trimmer ~31 minutes in, that section of the tube is the lamp driver and the trimmer adjusts the offset. I'm happy to see that in an amp as well! I've only seen that on discreet analog phasers, where you can use it to obtain the optimal on-off or ramping for the oscillator. This directly affects depth, yes, but also the overall waveform and feel of the tremolo. Here is an interesting article on bulb-offset adjustments in a Univibe pedal: (scroll a little more than halfway down to where it says "About the Bulb and Bulb Driver circuit")
EDIT:: you could also use different arrangements of optocouplers or lamp/LED/ and LDR combinations. The offset adjustment allows for maximum flexibility with components of wildly varied tolerances.
+Britt Rossman Thanks for your comment. You are correct. This adjustment would certainly be controlling the amount of voltage reaching the lamp in the opto-coupler. The more intense the voltage swing, the more intense the lamp will get, thus, the larger the change of resistance in the optical resistor side of the roach. This will have the overall effect of changing the depth of the tremolo...and that's a great point about using different components. You can't just go buy an optical tremolo roach usually. You have to roll your own if they go bad, so yes, this will allow you great flexibility! Excellent point!
Hey man, I just saw your video on the Gibson GA-20RVT amp. I just acquired one and tubes are missing but I was told it works. Do you still work on them and where are you located if you do so I can send it to you.
Had a 60's GA45RVT "Saturn" back in the day - bought it new at Durlauf's Music Store in downtown Louisville. No "guts" and heavy as a boat anchor! "Uninspiring tone" pretty much nails it...
Great trouble-shooting and guitar slingin` Brad. Keep em comin` brother.Cheers
+August Lyons Thanks for continuing to watch my silly, rambling videos, August!
Where are you located? Just picked one of these up for 300$ over the weekend. Not a steal but a good deal. Its got some issues but it plays lol. The reverb doesnt work. Just curious on where to start with that?
Hey Brad how are you. I'm a huge fan of your Channel and I was wondering if you could show me on the schematic where the bias components are and maybe on the circuit itself. I'm pretty sure i know where exactly it is located but don't know the components. Sincerely i will appreciate if you could. Thanks.
I had one of those. Super heavy build, real cool vinyl weave covering. Lent it to a buddy. Never came back. 35 years ago.
The 64' GA-19RVT sounded a lot better. Wonder what made Gibson go to a cheaper look?
One of these has popped up locally in the uk would you say it’s a good little amp for around the home and recording sounds killer when you play it?
Great amp after doing necessary work on it.
@@TheGuitologist so a good tech is needed thanks for the advice Brad love your work and playing
I just picked one of these up. I can’t even figure out how to get the chassis out of the cabinet! Unbolted the screws but I’m lost from there because this seems like it is locked in. Any help?
I have the Epiphone EA 600 rvt sister of Gibson amp. I need to repair it.i we oil do love to hear back from you to see how we could collaborate on this amp.
Looking at the Epiphone equivalent...very helpful, thanks for sharing!
The Epiphone is not the same amp! I have both and they are not at all the same!
Hello! I just bought me one of these amps. I have a few questions about it, and was wondering if there’s a way I could message you?
i have one mostly like this. i am afraid to turn it on. last i looked the boards looked like they were melting probably electrolytes. btw mine uses 2x 6bq5 and the reverb was EPIC!
Brad how does this ga 20rvt compare to ga 19rvt Falcon. in good working order ? How many Watts ? Volume ? Tone. I love the Falcon is this as good or close ?Thanks
Definately the original Footswitch. My GA20RVT has the exact same Footswitch.
Brad do you have a link to the schematic. Have one on the bench that is proving to be a bit more challenging than expected. Thanks.
elektrotanya.com/gibson_ga-20rvt_schematic.pdf/download.html
Great video - I have the 35 watt Lancer and rewired 6EU7's to 12AX7's - and removed the tone sucking arrays...now sounds great but cent get trem to work...PITA lol
Couple notes... The GA-35RVT isn't 35 watts. The numbers in the model name are just arbitrary. Not related to wattage. And if you want to service your tremolo, it should be similar to the trem in this amp: th-cam.com/video/mhKp0mB52bE/w-d-xo.html
I think yours is younger than mine. I have the braided wire version. Very VERY bright circuit. I want to tame that a little.
I am trying to trace down a problem with my reverb. It hums HEAVILY when I engage it.
Did you get yours fixed? Just bought one for 300$ over the weekend and the reverb doesnt work
The higher value cathode caps may be an attempt to reduce the brightness of the amp.
This amps interior and schematic looks identical to an Epiphone Electra that I picked up.
Pretty much every Gibson model from this period had an equivalent Epi model.
I have had 2 ga35 rvt lancers (still own one) about same age without tone filters. But in my amp every wire (even on transformers ) is cloth covered. In the minuteman in the video they look like plastic covered wires ande look much too fresh and new for such age..... Mine have wonderful reverb and tremolo but i not like the transformer PI...
Damn! Tone with the Tele was amazing!! 😊¯\_(ツ)_/¯👍
not bad for a 50 year old amp...
+Don Lee I know, right! Definitely a good version of the Minuteman.
Typical Gibson amp hodgepodge of tubes used. Not only did the schematics not fit the tube, but they were slopply wired, no wonder they went out of the amp business in 1967, never mind the tone sucker circuits they were using.
The same with the Epiphone line of amps in that period.
I think there was a decision to manufacture this line of amps again in house in Kalamazoo , rather than farm them out to other builders up to that period.
When they started up the new amplifier line, they may have used new hires to construct on the line.
Good thing that at least they got it rght on the humbucker and the Les Paul, .other wise they would have been extinct by now.
They almost went bankruptcy during the Norlin period in 1986, only survived after Henry J, and couple others decided to buy the company to continue production
and move guitar production to Memphis and Nashville.
These are very good-sounding amps once they've had some work done. This one, I think, proves that in the demo. Thanks for the comment! Agreed on the shoddy factory workmanship.
Really. If I wanted to learn guitar playing. I would have went to some thing different.
?