Solid State Cathodyne Phase Splitter Device?

ben_f_m · 9th February 2011, 10:00 PM

I'm working on an amplifier with what appears to be a solid state cathodyne phase splitter. It has +300VDC on one leg and -300VDC on the other, with the signal coming from a triode (12AX7) gain stage. The solid state device cannot be read. It's a TO-220 package or similar. What sort of solid state device would be appropriate in this application? Any recommendations for one to try?

aardvarkash10 · 9th February 2011, 10:58 PM

a very high voltage one - possibly a MOSFET.

kenpeter · 12:57 AM

IGBT survive the most insane of voltage... What value the resistors?

http://search.digikey.com/scripts/Dk...60hd&WT.srch=1

I guess even a MOSFET will do... Original more likely a MOSFET anyway.
Just cause IGBT is a newer lesser known device, definitely not inferior.

http://search.digikey.com/scripts/Dk...=497-5980-5-ND

Note IGBT is 50cents cheaper and half the capacitance of the MOSFET.

Eli Duttman · 10th February 2011, 12:29 AM

A 1 KV. rated MOSFET seems to be indicated. You want a part with a low reverse transfer capacitance. At 9 pF., this looks like a reasonable candidate. However, you did say the driving element will be a 'X7 section. I don't know if that low gm/high R_P triode has enough "stones". Frankly, the only MOSFET I'm comfortable with in combination with 'X7s is the ZVN0545A and that part can't handle the voltage described.

SY · 10th February 2011, 02:05 AM

With an effective C of 18pF, the f3 from a 12AX7 would be 140kHz or higher. Not tragic.

smoking-amp · 10th February 2011, 02:19 AM

Obtanium: 2.7 pF
http://www.fairchildsemi.com/ds/FQ/FQD1N80.pdf

Un-Obtanium: 2 pF
http://ixdev.ixys.com/DataSheet/98812.pdf

ben_f_m · 10th February 2011, 02:37 AM

Thank you all for your helpful responses.

The resistors are 23k's.

I had not thought of an IGBT. Does anyone have experience with them in an audio signal path application?

The other options look good too (and I'm always interested in more). The fun thing with solid state components is they're inexpensive and have only three leads, so I can try them all, if I'm careful.

ben_f_m · 10th February 2011, 02:43 AM

The IXYS mosfets are truly unavailable! Do you think one could hear a difference? It would be fun to try, if it were possible.

kenpeter · 03:24 AM

Obtainium $1.78 qty 1 (1200V 6pf reverse)
Digi-Key - 497-4353-5-ND (Manufacturer - STGF3NC120HD)

Nelson Pass built a very nice amp of IGBTs.
Complimentary pair was once available.
Not sure why P-IGBT was dropped?

12,000V P-Unobtainium?!? Silicon carbide: Go figure...
http://www.scientific.net/MSF.600-603.1187

For your circuit:
600V/(23K+23K) = 13mA max. (probably biased at half this amount)
300V*6.5mA = 1.95W max (and probably biased to idle on this peak).

Wonder what blew the original? Is there a Zenier Diode nearby?

kenpeter · 03:48 AM

Regarding 800V Fairchild 2.7pF FQD1N80 as "obtainiumed" by Smoking.
0 quantity at Digikey, 73cent TO-252 SMT at Mouser but no TO-220.

Only need 2W, why we wouldn't opt for a fully insulated package???

9th February 2011, 10:00 PM	#1
ben_f_m diyAudio Member Join Date: Mar 2009	Solid State Cathodyne Phase Splitter Device? I'm working on an amplifier with what appears to be a solid state cathodyne phase splitter. It has +300VDC on one leg and -300VDC on the other, with the signal coming from a triode (12AX7) gain stage. The solid state device cannot be read. It's a TO-220 package or similar. What sort of solid state device would be appropriate in this application? Any recommendations for one to try?

9th February 2011, 10:58 PM	#2
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	a very high voltage one - possibly a MOSFET. __________________ Yes, conservatism thrives on low intelligence and poor information. But the liberals in politics... continue to back off, yielding to the supremacy of the stupid. It's turkeys all the way down. - George Monbiot, guardian.co.uk, 6 Feb 2012

10th February 2011, 12:27 AM	#3
kenpeter diyAudio Member Join Date: Nov 2007 Location: Dallas	IGBT survive the most insane of voltage... What value the resistors? http://search.digikey.com/scripts/Dk...60hd&WT.srch=1 I guess even a MOSFET will do... Original more likely a MOSFET anyway. Just cause IGBT is a newer lesser known device, definitely not inferior. http://search.digikey.com/scripts/Dk...=497-5980-5-ND Note IGBT is 50cents cheaper and half the capacitance of the MOSFET. Last edited by kenpeter; 10th February 2011 at 12:57 AM.

10th February 2011, 12:29 AM	#4
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	A 1 KV. rated MOSFET seems to be indicated. You want a part with a low reverse transfer capacitance. At 9 pF., this looks like a reasonable candidate. However, you did say the driving element will be a 'X7 section. I don't know if that low gm/high R_P triode has enough "stones". Frankly, the only MOSFET I'm comfortable with in combination with 'X7s is the ZVN0545A and that part can't handle the voltage described. __________________ Eli D.

10th February 2011, 02:05 AM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	With an effective C of 18pF, the f3 from a 12AX7 would be 140kHz or higher. Not tragic. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

10th February 2011, 02:19 AM	#6
smoking-amp diyAudio Member Join Date: Dec 2001 Location: Hickory, NC	Obtanium: 2.7 pF http://www.fairchildsemi.com/ds/FQ/FQD1N80.pdf Un-Obtanium: 2 pF http://ixdev.ixys.com/DataSheet/98812.pdf __________________ Ohms Law V = I R

10th February 2011, 02:37 AM	#7
ben_f_m diyAudio Member Join Date: Mar 2009	Thank you all for your helpful responses. The resistors are 23k's. I had not thought of an IGBT. Does anyone have experience with them in an audio signal path application? The other options look good too (and I'm always interested in more). The fun thing with solid state components is they're inexpensive and have only three leads, so I can try them all, if I'm careful.

10th February 2011, 02:43 AM	#8
ben_f_m diyAudio Member Join Date: Mar 2009	The IXYS mosfets are truly unavailable! Do you think one could hear a difference? It would be fun to try, if it were possible.

10th February 2011, 02:55 AM	#9
kenpeter diyAudio Member Join Date: Nov 2007 Location: Dallas	Obtainium $1.78 qty 1 (1200V 6pf reverse) Digi-Key - 497-4353-5-ND (Manufacturer - STGF3NC120HD) Nelson Pass built a very nice amp of IGBTs. Complimentary pair was once available. Not sure why P-IGBT was dropped? 12,000V P-Unobtainium?!? Silicon carbide: Go figure... http://www.scientific.net/MSF.600-603.1187 For your circuit: 600V/(23K+23K) = 13mA max. (probably biased at half this amount) 300V6.5mA = 1.95W max (and probably biased to idle on this peak). Wonder what blew the original? Is there a Zenier Diode nearby? Last edited by kenpeter; 10th February 2011 at 03:24 AM.*

10th February 2011, 03:30 AM	#10
kenpeter diyAudio Member Join Date: Nov 2007 Location: Dallas	Regarding 800V Fairchild 2.7pF FQD1N80 as "obtainiumed" by Smoking. 0 quantity at Digikey, 73cent TO-252 SMT at Mouser but no TO-220. Only need 2W, why we wouldn't opt for a fully insulated package??? Last edited by kenpeter; 10th February 2011 at 03:48 AM.

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