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VT-25 linestage + step-down trafo
VT-25 linestage + step-down trafo
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Old 8th October 2006, 11:09 AM   #1
Klimon is offline Klimon  Belgium
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Location: Leuven
Default VT-25 linestage + step-down trafo


I'm contemplating a vt-25 linestage terminated by 4:1 step-down trafo. How many DBm should the transformer be able to handle in this circuit, no parafeed?

Thanks a lot!!!

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Old 8th October 2006, 12:35 PM   #2
Gluca is offline Gluca  Italy
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Working on that right now but using a ccs loaded VT62 (801A). Well, the answer depends on the gain you need.

If your source is 2Vrms (CD player) your VT25 will step that signal up by a factor of 8 (actually less) so your transformer will see 16Vrms ... or 25dBu if you like.

4:1? So this seems to be a 10K:600R tranny, make sure it has enough inductance to load the tube. I would consider to parafeed it btw.

For your info, the tranny I am going to use is a 7.5K:600R with +160H @ 30Hz (no gap).

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Old 9th October 2006, 07:55 AM   #3
Klimon is offline Klimon  Belgium
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Thanks for clearing that up Gianluca.

Looks like I'll better do things right the first place and save for some $$$ Lundahls

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Old 9th October 2006, 08:32 AM   #4
Zoran is offline Zoran  Serbia
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Location: Belgrade
If You use VT25 as preamplifier,
You can lower the Load resistance,
even the inductance of primary windings
(based on that and capacitance...)
You use the small voltage swing...
I wrote some article for Costruire
"designing high-end tube preamplifier"
i used 10Y like example...
with excelent results...
But the PDF is too large to post here
try to lower load line (and inductance)
bearing in mind the distorsion,
the dynamic load line You can see
with spice simulation...
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