Home » Audio » Thermionic Emissions » Why parafeed?
Why parafeed? [message #77793] Sat, 07 September 2013 22:02 Go to next message
steve f is currently offline  steve f
Messages: 219
Registered: May 2009
Master
The title says it all. Why? Why do so few manufacturers use them?

Steve
Re: Why parafeed? [message #77794 is a reply to message #77793] Sun, 08 September 2013 14:23 Go to previous messageGo to next message
gofar99 is currently offline  gofar99
Messages: 1353
Registered: May 2010
Location: Southern Arizona
Illuminati (3rd Degree)
Hi Steve, Cost is my guess. Plus a few other things that might complicate the design. The output device(s) will see two different inductors. Regardless of their respective values it will introduce anomalies. The primary benefits would be to SE amplifiers. Then the dc power would not have to go through the output transformer. This would make it possible to use a much smaller output trannie as you would not be likely to saturate it. In push-pull designs I see no value as if operated within spec. A PP output transformer should never saturate.

Good Listening
Bruce
Re: Why parafeed? [message #77856 is a reply to message #77794] Sat, 14 September 2013 19:11 Go to previous messageGo to next message
steve f is currently offline  steve f
Messages: 219
Registered: May 2009
Master
Thanks Bruce.
Re: Why parafeed? [message #86325 is a reply to message #77793] Sat, 14 October 2017 16:57 Go to previous messageGo to next message
Zohanna is currently offline  Zohanna
Messages: 39
Registered: August 2017
Baron
Wow, you guys are so savvy here that I'm embarrassed about my relative novice. Can someone explain Para feed to me? I don't even know what it is.. Confused
Re: Why parafeed? [message #87874 is a reply to message #86325] Tue, 24 April 2018 21:04 Go to previous message
hudelson2 is currently offline  hudelson2
Messages: 3
Registered: May 2016
Esquire
Normally the primary of the output transformer is connected to B+ voltage and the plate of the output tube. In a single ended amplifier there is direct current passing though the output transformer. There has to be a gap in the core to keep the core from being saturated. Then you need an expensive large transformer to pass low frequencies.

Parallel feed (parafeed) has the DC passing through a separate inductor from B+ voltage to plate of the output tube. There is a DC blocking capacitor to the output transformer. Since there is no DC passing through the output transformer no gap is required in the transformer core so the transformer can be smaller and cheaper.

See https://www.tubecad.com/2014/09/blog0308.htm for further explanations.
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