Magnatone Starlett Dead

[1WoodHippie]

Had a guy bring me a little Magnatone Starlet he needed help on. He attempted to put in an isolation transformer in it. Looks like he's got everything wired up correct but it's dead. No pilot light and heaters don't glow. (Note this amp uses the 35w4 rectifier)

All the grounds are now tied together at Chasis ground and the ground on the cord goes there also.
One of the outs of the ISO tranny go to ground and the other to the hot lug of the Pilot light.
He's removed the 270ohm and .05 cap from underneath the filter caps, then installed new 2 new filters tied to chasis ground.

I know the bulb is good. I've got 140VAC on all my heaters but they won't glow.

I've never had to tackle a iso tranny but it can't be that tough. I'm probably overlooking something obvious.

thanks in advance!

[Jazz P Bass]

You must be careful of what you call ground.

On the schematic, all of the components that have the vertical line with the three bars (like at the input jack) can be considered a chassis ground connection.



That is all.

Everything else that you would think is ground should be kept separate as they tie into L2 (Neutral/White) on the power cord.

(then installed new 2 new filters tied to chasis ground) This is wrong.

I cannot find these parts on the schematic. ( He's removed the 270ohm and .05 cap from underneath the filter caps)

Edit: found it, it's a 270K resistor.

The .01uf capacitor on the output tube plate should be removed.

[1WoodHippie]

Since it's got an ISO tranny installed, doesn't that basically do away with "neutral", since the 2 legs of the secondary on the ISO tranny are hot and ground?

[Enzo]

The way to install the iso is to wire the iso primary to the wall plug cord, then wire the iso secondary to the former power cord connections. Don;t go changing anything else, unless you know what you are doing.


You tried to make it more complicated than it rally was.


I don;t see a pilot light in the schematic.

That 0.01uf plate cap on the output tube might be there to drain off any radio stations that make it through the amp.


"I've got 140v on all my heaters" doesn;t tell me anything. What matters is the voltage across each heater, not the voltage to ground. And especially when you have reinvented what ground is. I suspect you may have interrupted the complete path for the series heater current.

[1WoodHippie]

wait, i just had the "light bulb coming on" moment. I think I get it now.

think I know what I need to do now.

thanks gang!

[Jazz P Bass]

Since it's got an ISO tranny installed, doesn't that basically do away with "neutral", since the 2 legs of the secondary on the ISO tranny are hot and ground?

The two legs of the secondary are technically L1 & L2.

They are not Hot & Ground.

They are both Hot.

Ground is a term that should be considered & reserved as a reference point.