Gibson G70

[gtrplayr1976]

Hey Folks ! Anyone know where I can find a Gibson G70 schematic/layout ?

Thanks !

[J M Fahey]

Here's the annotated power amp.

Can search for the preamp if you need it.

[Enzo]

Um... shouldn't Q6 be an NPN?

And are they not darlingtons?

[gtrplayr1976]

Thanks Juan ! I'll take all I can find. I'm coming up empty.

[J M Fahey]

Um... shouldn't Q6 be an NPN?

And are they not darlingtons?

Hey !!! this is the official GIBSON schematic!!!!!!
Don't tell me you know more than them !!!!
Just answer: did Eric Clapton and Jimi Page use a Gibson guitar or an Enzo guitar , huh ?????? <--typical TGP/MyLP/Harmony Central/etc. argument

Q3 , Q4 , and Q6 are NPN .
MJE1102/1092 are Darlingtons (notice the 1000/1200mV BE bias I expect to find there) and to boot are way underpowered for a 70W amp : 5A max current , "70W" , in that tiny smaller than TO220 case, like typical Peavey drivers .
They were notoriously unreliable (I wonder why ) and upgraded 3 times.
MJE1102 pdf, MJE1102 description, MJE1102 datasheets, MJE1102 view ::: ALLDATASHEET :::
I suggest TIP142/147 there, but pinout will no match, check both datasheets.

I posted what I found first, there's an old thread here, also search for other Gibson amps, there's one called something like G50/60/80 somewhere in MEF, all preamps were basically the same.

[gtrplayr1976]

Hey !!! this is the official GIBSON schematic!!!!!!
Don't tell me you know more than them !!!!
Just answer: did Eric Clapton and Jimi Page use a Gibson guitar or an Enzo guitar , huh ?????? <--typical TGP/MyLP/Harmony Central/etc. argument

Q3 , Q4 , and Q6 are NPN .
MJE1102/1092 are Darlingtons (notice the 1000/1200mV BE bias I expect to find there) and to boot are way underpowered for a 70W amp : 5A max current , "70W" , in that tiny smaller than TO220 case, like typical Peavey drivers .
They were notoriously unreliable (I wonder why ) and upgraded 3 times.
MJE1102 pdf, MJE1102 description, MJE1102 datasheets, MJE1102 view ::: ALLDATASHEET :::
I suggest TIP142/147 there, but pinout will no match, check both datasheets.

I posted what I found first, there's an old thread here, also search for other Gibson amps, there's one called something like G50/60/80 somewhere in MEF, all preamps were basically the same.

Thanks for the info. I'm trying to find out what the values of the two big can caps are ?

[J M Fahey]

Here's a Gibson G50/60/70/80 schematic, obviously a very different version under the same name.
It's in SSGuitar
Login
Gibson G-80
As said before, they kept replacing them under warranty, this one is a little stronger, used TIP33 powerhouse transistors .
Don't know which you actually have, a Darlington or a Discrete one?
Post a couple pictures.
For good measure, I'm adding G10/20/30 too so you have all the family.
By the way, what are you trying to fix?


PD: that said, yours might be *completely* unrelated

EDIT: that's the easiest part: 2200x50V or 4700x50V .

Tne earliest ones used large chassis clamp mounted electrolytics, modern ones will be radials 1/2 (or less) the size, solder their legs where approppriate.

Unless you want to keep the Mojo and insist on $65 a piece NOS Electrolytics.
If so, I also have a couple bridges you might interested in, you give me U$5000 in cash, in small denomination unmarked bills and then you can charge toll to cars using it, how's that?

[gtrplayr1976]

Here's a Gibson G50/60/70/80 schematic, obviously a very different version under the same name.
It's in SSGuitar
Login
Gibson G-80
As said before, they kept replacing them under warranty, this one is a little stronger, used TIP33 powerhouse transistors .
Don't know which you actually have, a Darlington or a Discrete one?
Post a couple pictures.
For good measure, I'm adding G10/20/30 too so you have all the family.
By the way, what are you trying to fix?


PD: that said, yours might be *completely* unrelated

EDIT: that's the easiest part: 2200x50V or 4700x50V .

Tne earliest ones used large chassis clamp mounted electrolytics, modern ones will be radials 1/2 (or less) the size, solder their legs where approppriate.

Unless you want to keep the Mojo and insist on $65 a piece NOS Electrolytics.
If so, I also have a couple bridges you might interested in, you give me U$5000 in cash, in small denomination unmarked bills and then you can charge toll to cars using it, how's that?

Thanks Juan ,I'm good on bridges lol
I'll get some pictures asap.

[gtrplayr1976]

Here are a couple of chassis shots.

[J M Fahey]

Ok, then you seem to have the same power amp as the original "orphan/annotated" schematic, because on ther right edge of the first picture I see 2 x TO92 transistors (Q3/Q4?) , a TO220 one (Q5?) , 2 puny small plastic transistors (TO126 case? ... ridiculous) 2 bias diodes clamped to chassis/heatsink and the very old style bias trimmer.
I'd replace the power transistors with TIP142/147 without even checking them, go figure.
Pay attention to pinout which does NOT match.

The preamp might match though:
2 DIP ICs
2 trimmer pots (reverb & tremolo)
5 TO92 transistors
1 heatshrinked *lamp*/LDR tremolo roach.

Oh well.

[gtrplayr1976]

Ok, then you seem to have the same power amp as the original "orphan/annotated" schematic, because on ther right edge of the first picture I see 2 x TO92 transistors (Q3/Q4?) , a TO220 one (Q5?) , 2 puny small plastic transistors (TO126 case? ... ridiculous) 2 bias diodes clamped to chassis/heatsink and the very old style bias trimmer.
I'd replace the power transistors with TIP142/147 without even checking them, go figure.
Pay attention to pinout which does NOT match.

The preamp might match though:
2 DIP ICs
2 trimmer pots (reverb & tremolo)
5 TO92 transistors
1 heatshrinked *lamp*/LDR tremolo roach.

Oh well.

Thanks Juan ! I don't have this amp in hand yet. It belongs to my cousin ,and I'm waiting for him to bring it to me. We'll get a parts list together also.

[gtrplayr1976]

Ok, then you seem to have the same power amp as the original "orphan/annotated" schematic, because on ther right edge of the first picture I see 2 x TO92 transistors (Q3/Q4?) , a TO220 one (Q5?) , 2 puny small plastic transistors (TO126 case? ... ridiculous) 2 bias diodes clamped to chassis/heatsink and the very old style bias trimmer.
I'd replace the power transistors with TIP142/147 without even checking them, go figure.
Pay attention to pinout which does NOT match.

The preamp might match though:
2 DIP ICs
2 trimmer pots (reverb & tremolo)
5 TO92 transistors
1 heatshrinked *lamp*/LDR tremolo roach.

Oh well.

I finally have this amp in hand. Looks like someone tried to mod? ,or repair at one time. Added caps ? Some places you can see were disconnected from the board ,and hardwired. May have to strip all the mods? ,and start over.

[gtrplayr1976]

Could Admin please move this ?

Could this thread be moved to repair ,and troubleshooting , or should I start another for repair help ?

Thanks !

[Leo_Gnardo]

Could this thread be moved to repair ,and troubleshooting , or should I start another for repair help ?

Thanks !

No admin here but you could start a new thread at the appropriate spot R&T, & put a link back to this thread for e-z reference. Costs nothin' but a minute of your time.

[gtrplayr1976]

No admin here but you could start a new thread at the appropriate spot R&T, & put a link back to this thread for e-z reference. Costs nothin' but a minute of your time.

Thanks Leo_Gnardo lol