Yamaha G50-112 owners manual wanted

[JoeM]

Dave,

I just got a scanner this week, so give me a few days and I'll scan and post them just in case anyone else may find the info useful.

[upstairsdave]

Hey Joe,
You da man!!! Thanks
Dave

[rami939]

Yamaha G50-112 II

Hi there,
is it easy to replace the 2 electrolytic caps on the G50-112 amp.?
What should I do to avoid an electric Zap from them.
I already have the replacement parts,but not sure how to proceed .
Thanks.

[upstairsdave]

I'd contact your local repair shop and ask their technician what you should do.
Do you know where I can find an input jack assembly for the G50?
Thanks
Dave

[JoeM]

Here's the scan. It's not real high-res to save some space, so if you can't read something let me know.

[rami939]

Yamaha G500112

I've just been working on mine,because there was a broken tip of a guitar cable inside the high input,and for what I saw,i think that you might have to buy a used amp and try somehow to swap it.,or see if an amp tech can do something for you,but it will cost you some money though.

[upstairsdave]

If I can't find the replacement part, I'll buy two input jacks and hard wire them using a schematic and following the circuit on the board. I'd most likely only use the first input jack anyway and use the volume to decrease the output.
I took out the A-B input jack to clean it and being it's a piece of crap plastic, I can't tighten the nut to hold it on the back. I ordered a stereo replacement jack from Mouser electronics and I'll replace it with a steel threaded mount. The speaker output jacks seem to be OK, so I'll leave them alone for now. I'm replacing all of the POTs so it should sound even better than it already does. I think someone spilled a beer or two on the front of the amp. Man is it crusty in there.
Here is Mouser site:
Mouser Electronics - Electronic Component Distributor
Here’s a list of the parts I ordered
Mouser #: 450-1171-GRX
Knobs & Dials .93D X .56H DELTA MK
10 knobs at $1.03 ea

Mouser #: 568-NYS234-3
Audio/Video Connectors 1/4 STEREO VERTICAL
1 $0.57 ea

Mouser #: 313-1600F-50K
Panel Mount Potentiometers Linear W/SW 50K PC Mount
3 $4.14 ea

Mouser #: 858-P160KN-0QC15B25K
Panel Mount Potentiometers 16mm Rotary Panel Potentiometer
4 $0.80 ea $3.20 1 extra for a spare

Mouser #: 652-PDB181-K420K102A
Panel Mount Potentiometers 1K SINGLE
2 $1.32ea $2.64 I extra

Mouser #: 858-P160KN0QC15B250K
Panel Mount Potentiometers 16mm Rotary Panel Potentiometer
4 $0.80ea $3.20 1 spare

Mouser #: 568-NYS234-3
Audio/Video Connectors 1/4 STEREO VERTICAL
1 $0.57ea $0.57 A-B input jack on rear of chassis

[rami939]

Yamaha G50-112

I finished changing the 2 big caps next to the power supply today,and now the amp runs quietly.

[upstairsdave]

How did you discharge them? Where did you get the caps and how much were they. I'd like to pick up two while they are still available.
Do you have the owners manual? It's not rocket science figuring out how to use he amp but it would be cool to have it.
Dave

[rami939]

the caps were dry(after 30 years),so there was not discharge,but,just in case,i attached the end of a piece of cable to the chassis of the amp,and the other end to one of my left fingers.You can get one of those wrist bands with a chord and a clip at the other end,but i was lazy and didn't want to drive to the store to buy one.
The 2 caps cost $10 + shipping @
http://www.tedss.com/item.asp?id=2020030884
these caps are 4700uf -100v,and are a bit bigger in diameter than the stock ones,so what i did was,to use the same round metal support ,I opened them up with my hand to make the new ones fit,and then drilled 1 new little hole in the chassis for each support because of the larger diam. .
It may sound like a lot of work,but trust me,it's not,is very easy to do,even for me that I had a hand surgery last Thursday,so,I basically use one hand.
By chance does anybody knows how to add a loop effects on the pre amp section of these amps?
I know is doable but don't know where to solder the in/out jacks.
Why do you want the owner's manual?Everything is old school,very simple on these,but not,I don't have one.

[upstairsdave]

What is the direct out on the back of the amp for. Is it to go to another amplifier or a sound board? What kind of pedal is necessary for reverb and for the A-B switch. Is the A-B a stereo cable type pedal.
It would still be cool to have a manual for the amp if an when I sell it.
Thanks
Dave

[J M Fahey]

Warning danger

,but,just in case,i attached the end of a piece of cable to the chassis of the amp,and the other end to one of my left fingers.You can get one of those wrist bands with a chord and a clip at the other end,but i was lazy and didn't want to drive to the store to buy one.

That is a sure fire way of getting gravely hurt or dead.
What you did is normally done to "discharge static" from *yourself* which is necessary when working with electrostatic-sensitive components such as microprocessors, etc. which was not the case here.
What everybody talks about is discharging *THE POWER SUPPLY CAPACITORS* in which case you must NOT touch them with your bare fingers at all.
You did exactly the opposite, you grounded very well your left hand (I assume you are right handed) creating a great path through your chest for any voltage your right hand might touch.
This particular amp, being single-supply, has close to 100 Volts on many points in its circuit.
You were lucky ... this time.

[rami939]

Well then,I've got lucky twice,because yesterday (Sunday) I did the replacement of the caps on my other Yamaha.
The funny thing is when I asked in this forum how to discharge them,nobody said a word.
I asked a friend,and he told me to do what I've explain before.
These amps(G50's) are about 30 years old(my other one is even older I think),and for anybody to expect that the original caps are still holding their own is a stretch since the life span of the caps is about 3000 hours.
But for the record,I'm left handed and that's the hand that I've insulated for that task.
Obviously the was not electric current running through them for a while(over a month).
I would do it this way now since the caps are new.

[JoeM]

Well then,I've got lucky twice,because yesterday (Sunday) I did the replacement of the caps on my other Yamaha.
The funny thing is when I asked in this forum how to discharge them,nobody said a word.
I asked a friend,and he told me to do what I've explain before.
These amps(G50's) are about 30 years old(my other one is even older I think),and for anybody to expect that the original caps are still holding their own is a stretch since the life span of the caps is about 3000 hours.
But for the record,I'm left handed and that's the hand that I've insulated for that task.
Obviously the was not electric current running through them for a while(over a month).
I would do it this way now since the caps are new.

Seriously, you did get lucky. On a tube amp you could have really hurt yourself. Learn how to properly discharge the filter caps if you ever work on one. You dont use an anti-static wrist strap for that at all!

[upstairsdave]

I put a response on the thread as follows:

I'd contact your local repair shop and ask their technician what you should do.
Do you know where I can find an input jack assembly for the G50?
Thanks
Dave
A capacitor is like a sponge. There is a negative side and a positive side. The both sides try to get to ground but they can't because they are insulated from each other. If you touch both terminals, you are the complete path to each other and ZAP!!!! Right through you. Look up capacitor s and how they work and how to discharge them on a google. There's tons of info out there. But then if a friend told you to do it the way you did, who would have thought.
Here you go.

discharging capacitors - Google Search