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In Reply to: RE: Dowdy choke for an headphone/preamplifier. posted by 5129 on July 07, 2016 at 13:50:36
Hi Michael,
The output transformer is your TL404, standard version.
The I on the plate of the tube could be between 35-40mA.
Thank you for your reply
Follow Ups:
The Dowdy choke is more than adequate for use with a TL-404.I could make you a plate choke with double, triple or quadruple the L but at great expense monetarily and an even greater cost in terms of performance.
The Achilles heel becomes at least twofold. As the size becomes greater and greater so doesn't the winding capacitances increase to the point where your tube would have difficulty driving the capacitance.
As the core becomes larger and larger the energy required to kickstart the core and supply the magnetizing current becomes a limiting factor.
Builder of MagneQuest & Peerless transformers since 1989
Edits: 07/07/16
Some times ago my friend measured the primary inductance of your tl404. He found about 27H.
So the anode choke and primary of the tl404 are in series in a parafeed design.
The total inductance isn't a great value.
But I trust you. If in your opinion the dowdy is great for my application (vt52 parafeed) i'm ready to buy a pair.
Have you got in stock a pair of dowdy chokes?Regards
Edits: 07/07/16 07/07/16
The two inductors (plate choke & output trans) are in parallel.
What was the signal level and frequency that you used to measure the L? What test instrument did you use?
To get true inductance readings you really need to use a professional inductance bridge and drive the unit under test properly.
Builder of MagneQuest & Peerless transformers since 1989
Sorry for the mistake….
I thought to parallel connection but i wrote series…..
We are speaking about parafeed design…
:-)
About the measurement, ASAP i'll send you more information about instrument that my friend used.
Thank you very much Michael,
Regards
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