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Old 22nd February 2011, 01:08 PM   #1
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Default REN904 for linestage?

REN904 (or similar) is an audio triode specifically made for transformer coupling. Would it be a good candidate for a linestage with a 30k:500 line output transformer, you think? The gain is approx 30x.

Vf 4
Af 1
Va 250
Vg -3.5
mAa 6
ra 12,500
gm 2.4




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Last edited by bequerel; 22nd February 2011 at 01:17 PM.
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Old 22nd February 2011, 01:42 PM   #2
kevinkr is offline kevinkr  United States
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Plate resistance is pretty high for use with full audio bandwidth transformers, building a 30K transformer that is reasonably flat over a range of just 20Hz - 20kHz would be very difficult.

Tubes with an rp half that of the REN904 or less would be much easier to source a transformer for.
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Old 22nd February 2011, 02:08 PM   #3
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[QUOTE=kevinkr;2478657)
Tubes with an rp half that of the REN904 or less would be much easier to source a transformer for.[/QUOTE]

In my experience tubes with an Rp around 6-7k (6SN7 for instance) are about the limit with inductive coupling. Plate chokes and dedicated 1:1 transformers will do, but everything else becomes problematic. The combination of high Rp and winding capacitance will result in loss of treble and/or early HF phase shift.
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Old 22nd February 2011, 02:34 PM   #4
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Bartolucci has a 30k/1200 transformer. Have look at type F here.
Data seems to be good.

Ricerca e Sviluppo - Bartolucci Transformers - Products List - Preamplifier OPTs
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Old 22nd February 2011, 03:26 PM   #5
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Bequerel,

Data of this transformer seems to be good, but in what regard?
It has some 240H of inductance, needed for bass response.
Frequency response is indicated to be -3 dB at 10 Hz.
But the problem, without doubt, will be "at the other side" of the spectrum.
Don't expect audio treble with a 12k Rp tube; we can't cheat nature.
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Old 22nd February 2011, 03:33 PM   #6
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Quote:
Originally Posted by pieter t View Post
Bequerel,

... we can't cheat nature.
No, you are sure right about that.
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Old 22nd February 2011, 04:40 PM   #7
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Hi!

Agree to the comments above. In addition:

To my taste the tube would not have enough headroom for linestage duty, especially if the volume control would be placed at the output.

Do you really need that much gain in a linestage?

Thomas
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Old 23rd February 2011, 06:39 AM   #8
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Originally Posted by Vinylsavor View Post
Hi!

Agree to the comments above. In addition:
...

Do you really need that much gain in a linestage?

Thomas
With the Bartolucci transformer the gain would have been approx. 6.
But I agree, you usually do not need that much gain either.
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