# Help me bring a YBA4 back to life!



## sj250 (Oct 26, 2010)

I scored this well loved gem off Kijiji for $80 with the full understanding it wasn't functioning. The owner had a few ideas of what it needed, 3 prong cord resoldered and transformer reattached to the chassis. I got it home, opened it up and he wasn't far off.

The issues he listed are correct, as well as both filter caps were loose as the retaining straps had broken. Also the ground lift switch is still wired in along with the 3 prong cord.

I have new filter caps on the way, I resoldered the 3 prong cord, grabbed a cord retainer for the chassis, and swapped in some old Mullard EL34's I've been hanging onto. At this point the only thing left to do is deal with the ground lift switch. I will admit straight up that my knowledge of amp wiring is very limited. That being said I'm fully aware of the dangers, safe working methods and can competently work on this myself following directions from those more knowledgeable.

It looks like the hot from the transformer has been swapped directly to the AC switch already. At this point judging from a few shiny solder joints I'm thinking the ground switch has been removed from the circuit for the most part but I'm assuming it wouldn't be a terrible idea to remove it completely while I'm in there. I will post a few pics and if anyone is willing to guide me in the right direction it would be greatly appreciated.





































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## jb welder (Sep 14, 2010)

Clip the yellow off at the circuit board. The green from the ground switch goes to the chassis? Clip it at the chassis.
One of the blacks from the ground switch goes to the AC switch? Clip it at the AC switch. Can ground switch now be removed from chassis?

Now where the yellow went in to the board and the white from the line cord is connected: clip off the white and the black (that goes to PT). Strip and connect white to black with a butt splice connector. No need to have neutral connecting to the board.


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## sj250 (Oct 26, 2010)

jb welder said:


> Clip the yellow off at the circuit board. The green from the ground switch goes to the chassis? Clip it at the chassis.
> One of the blacks from the ground switch goes to the AC switch? Clip it at the AC switch. Can ground switch now be removed from chassis?
> 
> Now where the yellow went in to the board and the white from the line cord is connected: clip off the white and the black (that goes to PT). Strip and connect white to black with a butt splice connector. No need to have neutral connecting to the board.


That's exactly what I had in my head, thank you for confirming it! The only other wire on the ground switch is the black one in the last photo running to the jumper wire with the 2 other blacks. You can definitely tell by the solder that has been messed with. 

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## jb welder (Sep 14, 2010)

sj250 said:


> The only other wire on the ground switch is the black one in the last photo running to the jumper wire with the 2 other blacks. You can definitely tell by the solder that has been messed with.


That black can be clipped off at the jumper wire on the board.


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## sj250 (Oct 26, 2010)

Thanks, I appreciate the help. Only issue now is replacing the bias filter cap. Currently a 68uf/63v and I can't find anything close. Closest so far is either 100/100 or 80/450v

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## jb welder (Sep 14, 2010)

100/100 is good.


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## MarkusV (Sep 24, 2009)

Agree
100/100 works well
I had a YBA 4 that I sold in a moment of stupidity.
It's one of the amps I miss most. Just Huge sounding with that 15 inch speaker. At around 6 on the volume it just rips ...Angus all the way

Markus


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## sj250 (Oct 26, 2010)

MarkusV said:


> Agree
> 100/100 works well
> I had a YBA 4 that I sold in a moment of stupidity.
> It's one of the amps I miss most. Just Huge sounding with that 15 inch speaker. At around 6 on the volume it just rips ...Angus all the way
> ...


I'm so excited to get this thing up and running again. Once I do I'll be kindly suggesting the wife and kids go for a play day at a friend's house, haha

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