Simple rule of thumb for phase of output transformer?

[sabredude]

I've built probably 4 amps in a row now that I've wired the output transformer backwards and had the amp do the whole oscillation thing. I understand why this happens (all had NFB) and I quickly reversed the leads on the power tubes to the transformer but is there a simple rule of thumb so I don't keep making the same mistake? Perhaps something like count the stages and if odd, reverse polarity if even leave alone? I know there's a polarity dot on the transformer but I still end up confused in the end.

Thanks!!

[Structo]

Yeah I've done it before.

I haven't built many amps but if the layout and schematic are right, then you get lucky.

You could use test leads with clips and hook up the OT at low volume and see if it oscillates.

If you have already cut and soldered the OT in place, you can also switch the two wires on the PI to switch the phasing.

[ic-racer]

If you can get a schematic of the transformer, sometimes it will give a clue. Sometimes the phase is actually indicated as below.
[img]http:370:233]http://softone.a.la9.jp/english/opt21.gif[/img]

[ic-racer]

Sometimes, only two dots are shown. For the Hammond, connect dot to dot for proper NFB response.

[briane]

theres no luck to it - basic layout.....pic would be better, but Ill try and describe

I dress each side of the PI out with a different color wire


say PI out (junc 220k & .1 cap) right red, left black...

then Power tubes same - right pair red, left black...

then OT blue right Power tubes, OT brown left tubes


just keep it straight, and do it the same each time.

hopefully you have brown and blue OT wires - most do.

and thats looking down as your wiring it....