GU-50 output trafo

croccodillo · 10th May 2007, 12:04 PM

Hi all,

I read everything I found about GU-50 tubes, here on the forum and on the net (I'm thinking to use them for my new amplifier).
The problem is that it is not clear to me the actual outrput impedance of such a tube: I found reference to a 10K, 5K, 2K transformers, and I don't know which is the right value.
The datasheet I found do not report any value for the output impedance, nor any graph for triode-strapped condition.
Can you help me?

Thanks in advance,
Giovanni

Colt45 · 10th May 2007, 06:43 PM

What topology are you planning on using them in?

Wavebourn · 10th May 2007, 06:49 PM

Hi Giovanni!

For pentodes (regulated G2):

GU-50 100W output and power transformers

For triodes with 400V plate voltage you'll probably need 2-3K CT

Tweeker · 11th May 2007, 07:09 AM

Triode curves.

croccodillo · 11th May 2007, 07:22 AM

Hi, thanks for the answer.
The topology will be a parafeed SE amplifier.
I would like to use two or more paralleled GU-50 as output tube, driven with a High Voltage CCS (not decided yet if use a solid state one or a tube one).
Output trafo will be a toroid (I found a good -and cheap- manufacturer here in Italy).
THIS is a draft of the idea I have.
The output tubes will have an idle voltage of about 300V (low, I know), while the CCS will work between 200 and 0V, with a current of 100mA.
I'm thinking to use two paralleled GU-50 tubes also for the upper CCS.
If I can keep the output impedance as low as 1K, I can have about 20W of RMS output power...

I don't know if use the GU-50 in pentode mode, triode-strapped mode, enhanced triode or whatever else comibnation of grid1, 2, 3 voltages...

My idea was to use them as triode as output tubes, and use pentode mode (if I will ever use tubes) for the CCS.

Ciao,
Giovanni

Boeing · 11th May 2007, 07:31 AM

Hi ! I am using my GU 50 SE tube amp with 3.5KOhm OPT, at 330V plate voltage. It sounds beautiful .
Regards.

croccodillo · 11th May 2007, 07:37 AM

Thanks boeing for the feedback; some more information?
Do you use a single tube? How is it connected (triode, pentode, what else)?

Ciao,
Giovanni

Boeing · 11th May 2007, 08:55 AM

Hi Croccodillo ! My tube amp is triod connection. My OPT has Ultra linner terminal, but I have never tried it.
Regards.

10th May 2007, 12:04 PM	#1
croccodillo diyAudio Member Join Date: Mar 2005 Location: Bergamo	GU-50 output trafo Hi all, I read everything I found about GU-50 tubes, here on the forum and on the net (I'm thinking to use them for my new amplifier). The problem is that it is not clear to me the actual outrput impedance of such a tube: I found reference to a 10K, 5K, 2K transformers, and I don't know which is the right value. The datasheet I found do not report any value for the output impedance, nor any graph for triode-strapped condition. Can you help me? Thanks in advance, Giovanni __________________ In Nomine Libertatis Vincula Edificamus, In Nomine Veritatis Mendacia Efferimus.

10th May 2007, 06:49 PM	#3
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Hi Giovanni! For pentodes (regulated G2): GU-50 100W output and power transformers For triodes with 400V plate voltage you'll probably need 2-3K CT __________________ The devil is not so terrible as his mathematical model! Wavebourn: We Create Creativity!

11th May 2007, 07:22 AM	#5
croccodillo diyAudio Member Join Date: Mar 2005 Location: Bergamo	Hi, thanks for the answer. The topology will be a parafeed SE amplifier. I would like to use two or more paralleled GU-50 as output tube, driven with a High Voltage CCS (not decided yet if use a solid state one or a tube one). Output trafo will be a toroid (I found a good -and cheap- manufacturer here in Italy). THIS is a draft of the idea I have. The output tubes will have an idle voltage of about 300V (low, I know), while the CCS will work between 200 and 0V, with a current of 100mA. I'm thinking to use two paralleled GU-50 tubes also for the upper CCS. If I can keep the output impedance as low as 1K, I can have about 20W of RMS output power... I don't know if use the GU-50 in pentode mode, triode-strapped mode, enhanced triode or whatever else comibnation of grid1, 2, 3 voltages... My idea was to use them as triode as output tubes, and use pentode mode (if I will ever use tubes) for the CCS. Ciao, Giovanni __________________ In Nomine Libertatis Vincula Edificamus, In Nomine Veritatis Mendacia Efferimus.

11th May 2007, 07:37 AM	#7
croccodillo diyAudio Member Join Date: Mar 2005 Location: Bergamo	Thanks boeing for the feedback; some more information? Do you use a single tube? How is it connected (triode, pentode, what else)? Ciao, Giovanni __________________ In Nomine Libertatis Vincula Edificamus, In Nomine Veritatis Mendacia Efferimus.

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10th May 2007, 06:43 PM	#2
Colt45 diyAudio Member Join Date: Feb 2002 Location: Canada	What topology are you planning on using them in?

11th May 2007, 07:31 AM	#6
Boeing diyAudio Member Join Date: Apr 2007	Hi ! I am using my GU 50 SE tube amp with 3.5KOhm OPT, at 330V plate voltage. It sounds beautiful . Regards.

11th May 2007, 08:55 AM	#8
Boeing diyAudio Member Join Date: Apr 2007	Hi Croccodillo ! My tube amp is triod connection. My OPT has Ultra linner terminal, but I have never tried it. Regards.

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