80's Yamaha G-100

[Valvehead]

Working on an early 80's ? G100 Yamaha combo. Looks just like the old JC120 Roland.

No reverb.

Tank tested bad--installed new tank.

wires test ok--tried swapping them.

reverb pot tests good.

tried shorting the rev jack on the back.

anyone have a schematic or familiar with these amps ??

[Enzo]

Should be two cables to the reverb pan. One is the drive and the other the return. Pull them off the reverb pan and hold them ready. Power the amp, set it up to play, turn reverb up midway. Touch the tip of each plug with your finger. One of them ought to makie hum out the speaker when you touch. That is the return cable and plugs into the OUTPUT jack on the pan. If neither hums, your return circuit is dead.

Play into the front of the amp, the drive cable opught to have the music signal on it. Does it?

You swapped the reverb pan. Are you sure it is an appropriate type?

Don't forget to test both reverb cables.

[Valvehead]

yes--there is the hum touching the return cable. pan is correct--i even tested the new pan. cables tets good from pcb to pan.

i will test to see if i have signal all the way to the drive cable here in a bit

[Valvehead]

ok---yes i get ac when playing---at the drive cable where it connects to the pcb .


now that i think about what you said...about the wrong type tank....

i took out an Accutronics. Ill go see if i can dig it out of the trash barrel.
I couldnt find the EXACT part #. lets just say it was 1AB222AB. the closest i could find was a (example) 1AB222AC . I think it was 1 letter off --and made by Belton.Same exact size, etc.. Could it be THAT different and not work at ALL ?


cant find old one------new tank is a Belton RBL2AB3C1B equivelent to a 4AB3C1B aCCUTRONICS

[g1]

4AB3C1B is for tube amps with a drive transformer, like vintage Fenders. The input impedance is very low. The second digit in the part number is probably the one that was off, it is the input impedance of the tank.
For a solid state amp you would need something with a higher input impedance to work.
I would guess probably a 4BB or 4EB even.
Maybe someone here will know the exact number.

[g1]

This sounds right: http://music-electronics-forum.com/t16899/#post138196

[Enzo]

I would think 4EB or even 4FB. These are solid state amps, they won;t have a tube driving a transformer as the drive stage.


Count my vote against an AB type as well. Go with EB.

[Valvehead]

thanks guys--i didnt consider tube vs ss when ordering...

[Valvehead]

ok--new tank is in--- no reverb. I dont have the scem for this-where shall i start testing?

EDIT---- god i am an idiot..........i didnt look inside the new tank--there was a piece of foam on the springs......

so it works, but... with the control on 10 , its not super big reverb,, sounds like the pot is on 3 instead of 10 . Anyway to boost it ?

[52 Bill]

Works but is low in effect, is where you start checking things like do you have the tank plugged in correctly? Did you get the correct tank? Which tank didi you finally order?

[Valvehead]

maybe im being picky...it seems to be fine...yes-i even swapped the 2 wires..

its the tank mentioned above.

I just am used to having TONS of reverb when its on 10

[Mick Bailey]

Here's what I've got on Yamaha. Already in PDF and I can't get CuteFTP to write out the files to post them directly for some reason. Could do with them being uploaded permanently onto this site as my location is extremely slow. Will leave them here for a few days.

G100_SM_E.pdf
G100-112(3)_Main_C.pdf
G100-112(3)_PCB_C.pdf
G100-212-2_SM_E.pdf

[g1]

its not super big reverb,, sounds like the pot is on 3 instead of 10 .

Recall playing another amp in that series long ago, I could be mistaken but seems to me the reverb was weak even on 10, especially at lower volumes. Nothing like what you get from a vintage Fender reverb. Your description of "sounds like the pot is on 3 instead of 10" is what I remember.

[Valvehead]

ok--in that case , ill call it fixed

[g1]

Does it have the distortion circuit with the switched pot? Apparently switching dist. on but not turning it up will boost the reverb.