REN904 for linestage?

bequerel · 01:17 PM

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

kevinkr · 22nd February 2011, 01:42 PM

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.

pieter t · 22nd February 2011, 02:08 PM

[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.

bequerel · 22nd February 2011, 02:34 PM

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

pieter t · 22nd February 2011, 03:26 PM

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.

bequerel · 22nd February 2011, 03:33 PM

Quote:

Originally Posted by pieter t

Bequerel,

... we can't cheat nature.

No, you are sure right about that.

Vinylsavor · 22nd February 2011, 04:40 PM

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

bequerel · 23rd February 2011, 06:39 AM

Quote:

Originally Posted by Vinylsavor

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.

22nd February 2011, 01:08 PM	#1
bequerel diyAudio Member Join Date: Sep 2003	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 __________________ Thanx! Last edited by bequerel; 22nd February 2011 at 01:17 PM.

22nd February 2011, 01:42 PM	#2
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	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. __________________ www.kta-hifi.net

22nd February 2011, 02:34 PM	#4
bequerel diyAudio Member Join Date: Sep 2003	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 __________________ Thanx!

22nd February 2011, 04:40 PM	#7
Vinylsavor diyAudio Member Join Date: Feb 2002 Location: Lindau	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 __________________ http://vinylsavor.blogspot.com/

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22nd February 2011, 02:08 PM	#3
pieter t diyAudio Member Join Date: Apr 2009	[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.

22nd February 2011, 03:26 PM	#5
pieter t diyAudio Member Join Date: Apr 2009	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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