Question of D3a driving 300B

Tubenstein · 21st January 2012, 03:31 PM

Hi!
What is the sensitivity of an amplifier with D3a (triode wired) 1:1 transformer coupled driving the a 300B in SE?

Assume output transformer primary is 3.5K or 5K.

Thanks!

euro21 · 21st January 2012, 06:12 PM

Depends on 300B operating point.

At 385V/70mA, no grid current (A1 mode), Ug= cca -80V (max. cca 57V RMS).
D3a (10mA, 155V), LL1160 (4:4.5) -> Au: about 50.

57/50=1.14 V RMS

Tubenstein · 22nd January 2012, 02:24 AM

Assume this is a transformer coupling amplifier with interstage. Between 437A and D3a, which one is consider as a better drive for 300B??

I heard the 437A needs 1:2 step up for optimal drive, but D3a triode wired is no needed.

commstech · 22nd January 2012, 06:26 AM

the 437A is unobtainium. when u can find them, they cost an arm or leg. Use the D3a in triode and they sound better than a lot of triode drivers i have tried for SET amps.

monolith61 · 22nd January 2012, 04:39 PM

Hello

It is always better to stick to a 1:1 IT topology if possible. A good bifilar wound transfomer has a fantastic bandwidth when driven from a resonably low impedance such as the triode wired D3A. We can achieve a 5Hz to over 300 kHz in such a case. The D3A is a nice sounding tube, not expensive and easy to source.

Kind regards, //WDC
________________________
www.monolithmagnetics.com

Tubenstein · 25th January 2012, 04:30 AM

This is kind of difficult to use 437A 1:1 transformer coupled since it has limit on voltage swing and requires some step up while driving the 300B.

Quote:

Originally Posted by monolith61

Hello

It is always better to stick to a 1:1 IT topology if possible. A good bifilar wound transfomer has a fantastic bandwidth when driven from a resonably low impedance such as the triode wired D3A. We can achieve a 5Hz to over 300 kHz in such a case. The D3A is a nice sounding tube, not expensive and easy to source.

Kind regards, //WDC
________________________
www.monolithmagnetics.com

21st January 2012, 03:31 PM	#1
Tubenstein diyAudio Member Join Date: Aug 2011	Question of D3a driving 300B Hi! What is the sensitivity of an amplifier with D3a (triode wired) 1:1 transformer coupled driving the a 300B in SE? Assume output transformer primary is 3.5K or 5K. Thanks!

22nd January 2012, 02:24 AM	#3
Tubenstein diyAudio Member Join Date: Aug 2011	437A and D3a?? Assume this is a transformer coupling amplifier with interstage. Between 437A and D3a, which one is consider as a better drive for 300B?? I heard the 437A needs 1:2 step up for optimal drive, but D3a triode wired is no needed.

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21st January 2012, 06:12 PM	#2
euro21 diyAudio Member Join Date: Sep 2004 Location: Budapest	Depends on 300B operating point. At 385V/70mA, no grid current (A1 mode), Ug= cca -80V (max. cca 57V RMS). D3a (10mA, 155V), LL1160 (4:4.5) -> Au: about 50. 57/50=1.14 V RMS

22nd January 2012, 06:26 AM	#4
commstech diyAudio Member Join Date: Oct 2002 Location: SINGAPORE	the 437A is unobtainium. when u can find them, they cost an arm or leg. Use the D3a in triode and they sound better than a lot of triode drivers i have tried for SET amps.

22nd January 2012, 04:39 PM	#5
monolith61 diyAudio Member Join Date: Nov 2011	Hello It is always better to stick to a 1:1 IT topology if possible. A good bifilar wound transfomer has a fantastic bandwidth when driven from a resonably low impedance such as the triode wired D3A. We can achieve a 5Hz to over 300 kHz in such a case. The D3A is a nice sounding tube, not expensive and easy to source. Kind regards, //WDC ________________________ www.monolithmagnetics.com

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