In Reply to: Autoformers: Need Technical Explanation.... posted by Dr. Toobz on September 15, 2009 at 16:53:05:
The grounds are not exactly "common" on an autoformer. Think of the secondary of your average run of the mill tube output transformer. You have 16, 8, 4, and common on the secondary. If, let's say, you had a solid state amp that worked its best at 16 ohms, you could drive the 16 ohm tap with the amplifier and connect your speakers where they need to go to properly load the amp.
Now if we look at applications in tube amps, the autoformer would be like an extended secondary, and in the case of the Quickie you have a winding with 8k, 500, 8, 0. (Initially I didn't wire in the secondary, so it was really 8k, 500, 0). The ground of the primary connects to the 8 ohm tap on the secondary, and the secondary common is now the ground for the autoformer.
The downside to all of this is that you cannot have any DC on the coil! If you have a SEX amp and have the manual handy, you will see that some effort has been made to supply the output grid with a negative bias and to leave the cathode grounded to get the most optimal performance from the autoformer. This is the main difference between an autoformer and an output transformer, the autoformer is devoid of isolation.
The other downside is that pulling a truly balanced output off an autoformer is quite the challenge.
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Topic - Autoformers: Need Technical Explanation.... - Dr. Toobz 16:53:05 09/15/09 (5)
- RE: Autoformers: Need Technical Explanation.... - Caucasian Blackplate 12:19:22 09/16/09 (3)
- On the other hand, - Skip Pack 13:26:38 09/16/09 (2)
- RE: Autoformers: Need Technical Explanation.... - ironbut 09:54:39 09/16/09 (0)