Re: transformer-coupled pre - Dave Davenport - Tubes Asylum

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Re: transformer-coupled pre

In Reply to: Re: transformer-coupled pre posted by spkrplus on August 20, 2002 at 19:11:22:

Jim,
YMMV, short for "Your Mileage May Vary" from the automobile ads in the '70s. They would make claims for their gas mileage and then cover themselves by saying "your mileage may vary." In the Internet world it has come to mean that I have certain opinions or perhaps results that are not universal and you may have a different experience.
In a traditional transformer stage the transformer primary is connected between the plate and the B+ power supply. All of the current that flows through the tube also flows through the transformer primary because the transformer is in series with the tube.
In a "parafeed", or parallel feed, connection the transformer is connected between the plate and ground. There is a separate path from the plate to the B+ supply and then to ground. Thus the transformer is connected in parallel with the tube and hence the name parallel feed. One other thing: a transformer that was just connected between the plate and ground would draw a lot of direct current which would saturate the transformer and perhaps also fry the transformer. So to eliminate any DC there is a capacitor in series with the transformer, either between the transformer and the plate or between the transformer and ground. This is called the parafeed capacitor. All of the direct current operating the tube flows through the power supply and none of the audio signal flows through the power supply. All of the audio signal (and none of the DC) flows through the transformer. I believe that keeping the audio signal out of the power supply is one of the big reasons that parafeed sounds so good. Another big reason is associated with transformer design but I'll leave that up the transformer experts.
I hope that this helps.
Dave

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Follow Ups Full Thread

Topic - transformer-coupled pre - spkrplus 17:33:04 08/20/02 (10)

Re: transformer-coupled pre - twystd 14:52:00 08/21/02 (0)

Re: transformer-coupled pre - pushpullltriode 19:31:42 08/20/02 (3)

Series or parallel-coupled? - spkrplus 07:38:31 08/21/02 (2)

Re: Series or parallel-coupled? - pushpulltriode 21:25:56 08/25/02 (1)

Elliano vs. EAR - Spkrplus 22:10:40 08/26/02 (0)

Re: transformer-coupled pre - Dave Davenport 18:44:28 08/20/02 (4)

Re: transformer-coupled pre - spkrplus 19:11:22 08/20/02 (3)

Re: transformer-coupled pre - Dave Davenport 19:58:25 08/20/02 (2)

Re: transformer-coupled pre - spkrplus 23:09:05 08/20/02 (1)

Re: transformer-coupled pre - JC Audio 08:05:04 08/21/02 (0)

Follow Ups

Re: transformer-coupled pre - Dave Davenport 19:58:25 08/20/02 (2)

Re: transformer-coupled pre - spkrplus 23:09:05 08/20/02 (1)

Re: transformer-coupled pre - JC Audio 08:05:04 08/21/02 (0)

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