I can't remember the last circus board repair D-Lab showed us. I think what I get the most out of the your videos Terry are the "look out for" and "make sure you check X" in your troubleshooting and repairs. Great stuff as always.
This was a great one Terry! We don’t always see these vintage Solid States often. This had some really wild stuff going on. Thanks for sharing your expertise on this non-tube amp!
Hi Terry, love your channel. Here's a bit of trivia regarding power cord grounding: Did you know that electrical codes in North America and Europe specify that equipment power cord grounds be bonded mechanically to the chassis via a dedicated (not shared) ground screw or stud, and must not be soldered. For stranded wire, a compression lug is recommended for the ground wire connection to the ground screw. The reasoning behind this specification is that, fault ground currents can be so high as to melt and blow out the solder bonding the ground wire to the equipment. With a disconnection, the cassis now becomes a shock hazard. You can't always count on a panel breaker to trip and interrupt the fault current soon enough to keep a soldered ground wire bonded to the chassis. Breaker trip currents are usually much higher than rated breaker currents. The specification is also there to safeguard against fault currents being applied to equipment from an external source. External fault currents can occur when several pieces of equipment are interconnected via cable and a ground fault occurs in one of them. If a grounding stud cannot be welded to the equipment chassis, then a dedicated screw can be used instead. The way to attach a grounding screw to a chassis is to drill and tap the chassis for the screw thread (say 8-32 NF). Bare metal must be exposed on the cassis for the head of the screw and the nut that locks the screw to the chassis. The grounding screw is attached to the chassis by screwing it all the way into the chassis, such that the screw head firmly seats on the exposed bare metal of the cassis. On the other side of the chassis, a star washer and nut are used to secure the grounding screw to the chassis. The entire assembly must be screwed together tightly. To bond the power cord ground wire to the chassis, slide the open hole of the ground wire terminal onto the cassis bonding screw and thread a nut behind the lug to clamp it down tightly to the chassis nut. Note that, only the power ground wire may be attached to the chassis ground bonding screw; no other ground may be attached to this screw.
A great video series, D-Lab is a wealth of knowledge for anyone looking to get a better grasp of electronics. Terry covers tidbits that the classroom tends to leave out. Thank you Terry.
I wondered early on when you said both output transistors had collectors to ground, yet they were a NPN/PNP pair. "Oh, well" I thought, "Terry's got the schematic in front of him, he'll do his usual methodical checks along the way and find out what's up." Sure enough, I wasn't disappointed. Good job, sir!
Thanks Terry! This video was very helpful. I just repaired a Gibson G-55 a friend gave me, along with some other projects. I hope to have a tube amp repair under my belt soon.
Hey Terry, I own a 4x10 version of this amp. Have a look for schematic/info for a Randall RG-60 Commander. Same amp, and these were built by Randall for Gibson, to the best of my knowledge.
Ah, after reading your comment, I did notice they have very similar color schemes and layout. I have a Randall Rg80PH head that I recapped and the amp is a masterpiece in terms of build quality, and it's an amazing sounding amp. Randall used the preamp design for the RG series in several models until the late 80s.
Nice troubleshooting on this amp Terry. Looks like someone once thought he could fix it without a schematic. Sounds great with that big old 15" speaker in it too!
Watching you use your meters has helped me out. I'm not very confident in some of the reading I get and find myself returning back to where I was testing the amp.
Great video. Lot's of folks sing the praises of the Tube amp and its vintage tone and feel. Then they put a solid state Drive pedal in front of it. LOL.
Years ago I rescued a SS Vox Cambridge that someone had rewired incorrectly. With the schematic in hand,I successfully brought back to life! It sounded great! I must say the 60s- 70s SS amps were not too bad. Your systematic troubleshooting this amp was exactly what a tech should follow! While watching this repair I thought to myself each step to take, which you took. Too bad the owner did not have you bring the reverb and tremolo back to life. Maybe find out what the relay did. It looked like the second output jack was for recording ? Love from NW Colorado. Thanxz
Nice to see some Solid State amps on your channel. I feel like I'm one of the only amp techs willing to mess with them on UA-cam. Granted, I like my tube amps too, but no hate for Solid State. I really liked my Standel.......and I did a smaller Gibson that was great.
Nice repair and presentation Terry. When I fix an amp like that I always wonder how long it’s been since it made sound? In your case you know that your coworker had it sitting for a looong time. Great to bring stuff back to life!
Thanks for this ! I wonder if the collectors to ground short measurement is explained by the fact that the shorted bridge was still in place at that point. Also if the outputs are all plastic body with no metal exposed, they would not need insulated mounting hardware. And finally, i noticed that on the schematic they drew the top output Q as PNP instead of NPN. I am learning from some of your other videos and thanks again!! Rob in Rochester NY
Great video!! I have the smaller G40, owned it since 1977. The G10 through G80 amps were built by CMI for Gibson. They had the reputation of sounding surprisingly good for being solid state. I always loved the sound of mine -it’s like a clean Princeton. I did my own re-cap and power cord replacement, but did not know about the flakey circus breaker! Thanks for this tip. I’ll be replacing mine with a fuse very soon. So what was that extra jack in the back? Mine had a hole covered by the model name sticker I used for a speaker jack. Maybe I shouldn’t have defaced it like that. I turned my friend onto the Gibson Super Thor bass amp with two 15” that looks almost identical. The “G” models that end with a ‘0’ seem to be blackface, and the models ending with a ‘5’ are silverface (G-55, 105, 115). Hmmmmmm . . . Gibson Blackface /Silverface, I think I just invented something new!
It looked like the added jack and relay circuit was connected near the LDR. I take it this amp has a tremolo/vibrato effect built in? So I'd wager it was an extra footswitch to switch that circuit on/off. Also, should definitely wire the amp with a 3-way prong for proper safety grounding.
The factory jack in the back panel for reverb and tremolo was a TRS (Tip, Ring, Sleeve “stereo”) that connected to a dual button footswitch. There is not ONE picture on the internet of a 70’s Gibson solid state amp dual footswitch (there is one, but not branded as Gibson). Maybe CMI/Gibson provided no footswitch? I bought my amp used and it came with a Linemaster L-2-D footswitch. I always thought it came from Gibson, but maybe the reseller added it. It works surprisingly well. Of all the pictures on the internet the hole I found is always covered with the model name. I always wondered what they might have intended it for. It’s in a mildly inconvenient place for a speaker jack.
I have the Epiphone EA 600 Rvt Maxima it's the sister amp of Gibson's ga 600 rvt and its beautiful and needs work but i wouldn't part with it ever. Great looking amps they were building then and SS amps from that era are becoming very rare.
I have a similar Gibson SS amp that ate it's voice coil due to the aforementioned DC. If I remember correctly they used JBL speakers with a Gibson sticker slapped on them.
@D-Lab…I have purchased two older (early1950’s) radios. One is a Zenith Trans-Oceanic non leather case and one RCA Victor, leather covered that is similar to the Zenith. I would like to get them both restored. Can you do this?
I repaired one of these a few years ago and it's still at my shop. The outputs were blown and had to replace most of the pots too. The reverb is pretty noisy and I suspect the reverb IC is the culprit, but I can't find a suitable replacement (out of production). I replaced all the res and caps in that circuit but no luck. Other than that, it's all original. Replacing board mounted components requires unmounting the outputs and remounting to test with a signal. If I had some female pins of the right size I could have soldered them to the wires leading to the outputs and just removed them with every board pull.
Hey Terry - really nice job !!! Are you loving that Cable restraint tool ? Makes it easy work for sure. You've done a nice job with that amp.... I did notice there was a sticker in there that said G80, handwritten ... I wonder if someone tried their own upgrade from a G60 to a G80..... crazy kids.....
Hey, nothing wrong with solid state, they're just different. Besides, every transistor amp means more replacement tubes are out there for those kind of amps!
OMG, Terry, you did a 'boo-boo' talking about your lead guitar player giving up his Fender Princeton for the Gibson G-60......tsk, tsk ! ! ! ! I'll take a valve amp over any SS amp ! Another great job by Terry @ D-Labs ! ! ! !
I have a Epiphone EA-600 RVT that has a blown Motorola mr1033b rectifier Diode and it powers up but blows the fuse immediately. I would really appreciate your help with some pointers on fixing it. I love these videos you put out. I have electrical knowledge and know how so i can do the repair but need some questions answered also i have the Schematic for it
Bit of an odd choice to be replacing the heatsinked rectifier with discrete diodes of rather limited power dissipation to be honest... the original 50-year-old part may be obsolete but these square bridge rectifiers with center hole have remained super common, especially for 10-15 amps up.
Great channel and vids..I have a problem with my solid state Roland Cube 15 amp..when i turn it on it sounds like a machine gun and there is no sound from guitar. ? do you have a clue what might cause this. Regards.
Did you forget Power Light?? Can you find me a schematic for a Woodson 150-2 / Solid State Amp?? I have a 6o cycle hum ....I’m thinking Filter Capacitors??
No joke, I've also found a cut lead floating around loose before in one of these solid state Gibson amps from the same era. I think it was a G20? The 1x10 combo. They must have been really driving those workers to make these things in a hurry.
How did you manage to clean the pots? I'm working on a G70 and the pots will not clean up regardless what I try cleaning them with. Good work by the way, your work is always top notch.
I see your new line chord is the EU colour coded type brown, blue, green. Is the US adopting this colour scheme? In the UK the live wire used to be red, obviously for danger, I don't know why the EU thought brown would be better!
@@danielsaturnino5715 Not on the same scale, but a friend asked me to fix one channel on a stereo receiver he'd picked up at a flea market. After troubleshooting, I replaced a small signal transistor in a TO-92 plastic case with what should have been a functional equivalent replacement. Turned power on, and SNAP! Where the transistor had been was just the three tiny leads, the case was blown completely off! That was around 1977, so long ago that I don't recall if I ever got it working or not.
Hi D-Lab I encaunting a problem with my Peavey transtube it whent to a clip mode and it doesn't go away by turning it off even if it doesn't have a guitar plug in it,any suggestion.
I had a heath TA 16 from that same era. Kind of similar design. I know he used music man, but maybe they all sort of followed the same thought patterns. Very interesting, Gibson did some weird stuff in the early 70s
I can't remember the last circus board repair D-Lab showed us. I think what I get the most out of the your videos Terry are the "look out for" and "make sure you check X" in your troubleshooting and repairs. Great stuff as always.
This was a great one Terry! We don’t always see these vintage Solid States often. This had some really wild stuff going on. Thanks for sharing your expertise on this non-tube amp!
Hi Terry, love your channel. Here's a bit of trivia regarding power cord grounding:
Did you know that electrical codes in North America and Europe specify that equipment power cord grounds be bonded mechanically to the chassis via a dedicated (not shared) ground screw or stud, and must not be soldered. For stranded wire, a compression lug is recommended for the ground wire connection to the ground screw. The reasoning behind this specification is that, fault ground currents can be so high as to melt and blow out the solder bonding the ground wire to the equipment. With a disconnection, the cassis now becomes a shock hazard.
You can't always count on a panel breaker to trip and interrupt the fault current soon enough to keep a soldered ground wire bonded to the chassis. Breaker trip currents are usually much higher than rated breaker currents. The specification is also there to safeguard against fault currents being applied to equipment from an external source. External fault currents can occur when several pieces of equipment are interconnected via cable and a ground fault occurs in one of them.
If a grounding stud cannot be welded to the equipment chassis, then a dedicated screw can be used instead. The way to attach a grounding screw to a chassis is to drill and tap the chassis for the screw thread (say 8-32 NF). Bare metal must be exposed on the cassis for the head of the screw and the nut that locks the screw to the chassis. The grounding screw is attached to the chassis by screwing it all the way into the chassis, such that the screw head firmly seats on the exposed bare metal of the cassis. On the other side of the chassis, a star washer and nut are used to secure the grounding screw to the chassis. The entire assembly must be screwed together tightly.
To bond the power cord ground wire to the chassis, slide the open hole of the ground wire terminal onto the cassis bonding screw and thread a nut behind the lug to clamp it down tightly to the chassis nut. Note that, only the power ground wire may be attached to the chassis ground bonding screw; no other ground may be attached to this screw.
A great video series, D-Lab is a wealth of knowledge for anyone looking to get a better grasp of electronics. Terry covers tidbits that the classroom tends to leave out. Thank you Terry.
I wondered early on when you said both output transistors had collectors to ground, yet they were a NPN/PNP pair. "Oh, well" I thought, "Terry's got the schematic in front of him, he'll do his usual methodical checks along the way and find out what's up." Sure enough, I wasn't disappointed. Good job, sir!
That is beautiful bridge rectifier you built Terry. Going to steal that one.
Transistor amp repair, wow, good job! Loved the look on Tony's face at the end. Talk about caught in a bind.
Thanks Terry! This video was very helpful. I just repaired a Gibson G-55 a friend gave me, along with some other projects. I hope to have a tube amp repair under my belt soon.
My family looks forward to all your educational videos. Thank you for sharing your wisdom with us!!! We want more:)
Hey Terry, I own a 4x10 version of this amp. Have a look for schematic/info for a Randall RG-60 Commander. Same amp, and these were built by Randall for Gibson, to the best of my knowledge.
Ah, after reading your comment, I did notice they have very similar color schemes and layout. I have a Randall Rg80PH head that I recapped and the amp is a masterpiece in terms of build quality, and it's an amazing sounding amp. Randall used the preamp design for the RG series in several models until the late 80s.
Some power transistors do not require insulated mounting hardware. This could be the reason there were metal screws holding the transistors in.
Fantastic video, Terry, thanks for sharing so much of your expertise.
Nice troubleshooting on this amp Terry. Looks like someone once thought he could fix it without a schematic. Sounds great with that big old 15" speaker in it too!
Always something good to watch on D-LAB it's better than T.V. thanks Terry.
Watching you use your meters has helped me out. I'm not very confident in some of the reading I get and find myself returning back to where I was testing the amp.
Terry another awesome video thank you I learned alot about these solid state amps.
Great video. Lot's of folks sing the praises of the Tube amp and its vintage tone and feel.
Then they put a solid state Drive pedal in front of it. LOL.
Years ago I rescued a SS Vox Cambridge that someone had rewired incorrectly. With the schematic in hand,I successfully brought back to life! It sounded great! I must say the 60s- 70s SS amps were not too bad. Your systematic troubleshooting this amp was exactly what a tech should follow! While watching this repair I thought to myself each step to take, which you took. Too bad the owner did not have you bring the reverb and tremolo back to life. Maybe find out what the relay did. It looked like the second output jack was for recording ? Love from NW Colorado. Thanxz
Nice to see some Solid State amps on your channel. I feel like I'm one of the only amp techs willing to mess with them on UA-cam. Granted, I like my tube amps too, but no hate for Solid State. I really liked my Standel.......and I did a smaller Gibson that was great.
First:) thx terry your videos help in this hard time 4 everyone and especially myself. Hope you have a great day!!
Very cool video and a surprisingly good sounding amp. Interesting and intelligent repair. Love your work. Thanks.
You're the best! I appreciate your work.
Love the videos. I'm trying to learn a lil more about amp repair.
It sounds nice. I'm surprised the filter caps still work.
Nice repair and presentation Terry. When I fix an amp like that I always wonder how long it’s been since it made sound? In your case you know that your coworker had it sitting for a looong time. Great to bring stuff back to life!
Thanks for this ! I wonder if the collectors to ground short measurement is explained by the fact that the shorted bridge was still in place at that point. Also if the outputs are all plastic body with no metal exposed, they would not need insulated mounting hardware. And finally, i noticed that on the schematic they drew the top output Q as PNP instead of NPN. I am learning from some of your other videos and thanks again!! Rob in Rochester NY
Great video!! I have the smaller G40, owned it since 1977. The G10 through G80 amps were built by CMI for Gibson. They had the reputation of sounding surprisingly good for being solid state. I always loved the sound of mine -it’s like a clean Princeton. I did my own re-cap and power cord replacement, but did not know about the flakey circus breaker! Thanks for this tip. I’ll be replacing mine with a fuse very soon. So what was that extra jack in the back? Mine had a hole covered by the model name sticker I used for a speaker jack. Maybe I shouldn’t have defaced it like that. I turned my friend onto the Gibson Super Thor bass amp with two 15” that looks almost identical. The “G” models that end with a ‘0’ seem to be blackface, and the models ending with a ‘5’ are silverface (G-55, 105, 115). Hmmmmmm . . . Gibson Blackface /Silverface, I think I just invented something new!
It looked like the added jack and relay circuit was connected near the LDR. I take it this amp has a tremolo/vibrato effect built in? So I'd wager it was an extra footswitch to switch that circuit on/off. Also, should definitely wire the amp with a 3-way prong for proper safety grounding.
The factory jack in the back panel for reverb and tremolo was a TRS (Tip, Ring, Sleeve “stereo”) that connected to a dual button footswitch. There is not ONE picture on the internet of a 70’s Gibson solid state amp dual footswitch (there is one, but not branded as Gibson). Maybe CMI/Gibson provided no footswitch? I bought my amp used and it came with a Linemaster L-2-D footswitch. I always thought it came from Gibson, but maybe the reseller added it. It works surprisingly well. Of all the pictures on the internet the hole I found is always covered with the model name. I always wondered what they might have intended it for. It’s in a mildly inconvenient place for a speaker jack.
I have the Epiphone EA 600 Rvt Maxima it's the sister amp of Gibson's ga 600 rvt and its beautiful and needs work but i wouldn't part with it ever. Great looking amps they were building then and SS amps from that era are becoming very rare.
I have a similar Gibson SS amp that ate it's voice coil due to the aforementioned DC. If I remember correctly they used JBL speakers with a Gibson sticker slapped on them.
ive been watching soo long, i can tell Tony was playing on the intro! LOL!
Hey, this thing sounds pretty good. Reminds me of the Lab L series amps that BB King used. Very, very clean with a pretty fat frequency response.
@D-Lab…I have purchased two older (early1950’s) radios. One is a Zenith Trans-Oceanic non leather case and one RCA Victor, leather covered that is similar to the Zenith. I would like to get them both restored. Can you do this?
Hey Terry, do you have a video on 'Death Caps' ??
I repaired one of these a few years ago and it's still at my shop. The outputs were blown and had to replace most of the pots too. The reverb is pretty noisy and I suspect the reverb IC is the culprit, but I can't find a suitable replacement (out of production). I replaced all the res and caps in that circuit but no luck. Other than that, it's all original. Replacing board mounted components requires unmounting the outputs and remounting to test with a signal. If I had some female pins of the right size I could have soldered them to the wires leading to the outputs and just removed them with every board pull.
You stepped quietly through that one with good results. Thanks for the look.
I have this exact same amp! It powers up with a horrible loud buzz/hum so it is in need of some help. I'd love to get it back in action!
Terry, can you tell us non-SS types which leads you were testing across on the power transistors?
Hey Terry - really nice job !!! Are you loving that Cable restraint tool ? Makes it easy work for sure. You've done a nice job with that amp.... I did notice there was a sticker in there that said G80, handwritten ... I wonder if someone tried their own upgrade from a G60 to a G80..... crazy kids.....
I was curious to see what you were going to do with that relay mod and the 2nd input jack.
Yep, just left it, sorry
@@d-labelectronics =by
Any ideas about my question brother
I'm glad to see this cause I'm a solid state sinner :-)
Hey, nothing wrong with solid state, they're just different. Besides, every transistor amp means more replacement tubes are out there for those kind of amps!
OMG, Terry, you did a 'boo-boo' talking about your lead guitar player giving up his Fender Princeton for the Gibson G-60......tsk, tsk ! ! ! ! I'll take a valve amp over any SS amp ! Another great job by Terry @ D-Labs ! ! ! !
How about the burned out pilot light?
Replaced with new neon
I have a Epiphone EA-600 RVT that has a blown Motorola mr1033b rectifier Diode and it powers up but blows the fuse immediately. I would really appreciate your help with some pointers on fixing it. I love these videos you put out. I have electrical knowledge and know how so i can do the repair but need some questions answered also i have the Schematic for it
Bit of an odd choice to be replacing the heatsinked rectifier with discrete diodes of rather limited power dissipation to be honest... the original 50-year-old part may be obsolete but these square bridge rectifiers with center hole have remained super common, especially for 10-15 amps up.
You the man terry
Great video. Thank you.
Great channel and vids..I have a problem with my solid state Roland Cube 15 amp..when i turn it on it sounds like a machine gun and there is no sound from guitar. ? do you have a clue what might cause this. Regards.
Did you forget Power Light?? Can you find me a schematic for a Woodson 150-2 / Solid State Amp??
I have a 6o cycle hum ....I’m thinking Filter Capacitors??
have you not tried gibson ga-50 60 70 80 transistore sch - Elektrotanya
No joke, I've also found a cut lead floating around loose before in one of these solid state Gibson amps from the same era. I think it was a G20? The 1x10 combo. They must have been really driving those workers to make these things in a hurry.
It could have happened during the modifications that had been done to it.
A sweet little ditty
How did you manage to clean the pots? I'm working on a G70 and the pots will not clean up regardless what I try cleaning them with. Good work by the way, your work is always top notch.
I see your new line chord is the EU colour coded type brown, blue, green. Is the US adopting this colour scheme? In the UK the live wire used to be red, obviously for danger, I don't know why the EU thought brown would be better!
I wonder what would happen if you had those transistors connected to chassis with the 3 prong chord...
KaBoom!
Sounds like a job for ElectroBOOM
You'd just have a very high current fusible link; the chassis! 😨
@@bobblum5973 , I'd say the transistors would behave like firecrackers :)
@@danielsaturnino5715 Not on the same scale, but a friend asked me to fix one channel on a stereo receiver he'd picked up at a flea market. After troubleshooting, I replaced a small signal transistor in a TO-92 plastic case with what should have been a functional equivalent replacement. Turned power on, and SNAP! Where the transistor had been was just the three tiny leads, the case was blown completely off! That was around 1977, so long ago that I don't recall if I ever got it working or not.
Great sir
That's a rare model, I have all the Gibson schematics I thought. No solid state ones though. I do have a 1947 Gibson BR6 amplifier I restored.
Hi D-Lab I encaunting a problem with my Peavey transtube it whent to a clip mode and it doesn't go away by turning it off even if it doesn't have a guitar plug in it,any suggestion.
i would shorten the transistor leads
I had a heath TA 16 from that same era. Kind of similar design. I know he used music man, but maybe they all sort of followed the same thought patterns. Very interesting, Gibson did some weird stuff in the early 70s
I hear “Heartbreaker” by Grand Funk Railroad.
I didn't even know solid state amps had death caps!!! SHOCKING!!!!!!!!!!!!!!
is it dual supply + g -
Solid state shenanigans
ok ok i got it two cap body ground pnp and npn complimentary....its dual supply
Tony!
What's with the inductors, I mean long wires, on the output transistor leads? Good recipe for ultrasonic oscillation!
Seeing that makes me think some one did it for some nasty reason I have seen it my self.
Cup of tea??? What's happened, Terry?
This guy TONY is HORRIBLE!!! Find someone else. LOVE THE CHANNEL
As a qualified repairs engineer what really annoys me when all the people that are not qualified mess around with electrical equipment
prolly sabotaged when it was made , there was some of that in US made stuff in the 1970s when labor and companies had arguments........