1176 Power Supply Repair

[Rob Flinn]

Several years ago I found a LED replacement for the famous #47 bayonet bulb and I installed it behind the "jewel" of a friend's Fender (model forgotten) guitar amp. Wow that was bright.

Bri

Did you notice any ufo's trying to land in the vicinity when it was switched on ? Haha

 

[Cqwet Dbdfte]

I think at some point in the near future, a small utility PCB designed to replace the 30v Zener rail with the Rev G design would be in order! Seems like that’s a better/safer bet moving forward.

An LM431, a MOSFET plus 2 resistors can replace any Zener.

 

[CJ]

You can use vellum paper to diffuse light,

 

[Brian Roth]

You can use vellum paper to diffuse light.

We put a small piece of toilet paper behind the jewel.

Bri

 

[David Kulka]

If the new zener doesn't fix this, check to make sure that nothing after the zener is drawing excess current. Sometimes an output transistor will short, pulling DC current through the power transformer. Or possibly you have leaky filter capacitor.

 

[kags]

+1 on checking output transistor. I spent hours chasing that down on one unit. The bad transistor pulled the 30 V rail down to around 26V if I remember correctly.

 

[corgan4321]

If the new zener doesn't fix this, check to make sure that nothing after the zener is drawing excess current. Sometimes an output transistor will short, pulling DC current through the power transformer. Or possibly you have leaky filter capacitor.

Thanks David, I just installed the new Zener from you and it’s got the voltage up to 32.4V, technically out of spec according the 1176 manual stating 30v +/- 0.5v but better than what I had previously.

 

[David Kulka]

It that bothers you I'll select one that's closer and we can exchange them. But the slightly higher voltage won't really be an issue.

 

[corgan4321]

It that bothers you I'll select one that's closer and we can exchange them. But the slightly higher voltage won't really be an issue.

Thanks David! I’ll roll with it - seems to be working well now.