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

Hi,

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!!!

Simon
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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).

Ciao
Gianluca
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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

Simon
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Old 9th October 2006, 08:32 AM   #4
Zoran is offline Zoran  Serbia
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If You use VT25 as preamplifier,
You can lower the Load resistance,
even the inductance of primary windings
(based on that and capacitance...)
because:
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
*
tip
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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