SEX 2.0 Power Transformer Question

[Williston]

Hi,

I'm rebuilding a SEX amp that I originally built in 2006. In doing a voltage check I found low voltages on the transformer terminals 6 and 9. AC voltages should be 163 on both; I have 113 on 6 and 134 on 9. Voltage coming in on power terminal 1 is AC 120.2.

I measured my other SEX amp (I've built two) and got AC 174 on both 6 & 9.

Is this a transformer problem? It is 8 years old.

Thanks for any help.
Peter

[Doc B.]

Hi Peter,

The only way to be sure is to disconnect the red wire from each high voltage secondary to disconnect it from the power supply and amp circuit, and measure the voltage at each secondary again. If it goes up the transformer is fine and the problem is downstream of that - maybe old filter caps. If the voltage of the high voltage secondaries does not go up when disconnected, then yes it is transformer related.

[Williston]

And there it is. Disconnected the red wire and voltages on both went up to AC 175.

I had mistakenly thought that nothing downstream would affect voltages at the transformer terminals—shows what I know.

OK—thanks Doc. Think I'll just pull out the whole B+ section and re-build it.

Sorry for posting in the wrong section.

Thanks again for the very quick reply.

Peter