Which tubes for this OPT?

likeDIY · 15th November 2007, 02:02 AM

Hi dudes.
I got a pair of 3,2K/8Ohm, 100mA OPT, but i'm a bit reluctant choosing the rite tubes for it. Any ideas which one should I go with? probably easy with EL34, 6B4G, but I'm thinking of EL34 PSE, not sure if the OPT can handle 2 EL34/channel?

Any comments are appreciated.
Thanks.

Eli Duttman · 15th November 2007, 02:29 AM

A 300B with 350 V. on the plate, - 74 V. on the grid, and I_B = 60 mA. working into a 3 KOhm load yields 8.3 W. 3.2 KOhm is certainly close enough for the load.

You could go the combination bias "route", with an unbypassed 330 Ohm resistor under the cathode and the rest of the bias voltage coming from a negative supply. The local current NFB (degeneration) associated with the unbypassed cathode resistor raises the effective plate resistance, which would mate nicely with that "extra" 200 Ohms. The improved linearity local NFB yields aids the cause too.

15th November 2007, 02:02 AM	#1
likeDIY diyAudio Member Join Date: Sep 2006	Which tubes for this OPT? Hi dudes. I got a pair of 3,2K/8Ohm, 100mA OPT, but i'm a bit reluctant choosing the rite tubes for it. Any ideas which one should I go with? probably easy with EL34, 6B4G, but I'm thinking of EL34 PSE, not sure if the OPT can handle 2 EL34/channel? Any comments are appreciated. Thanks.

15th November 2007, 02:29 AM	#2
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	A 300B with 350 V. on the plate, - 74 V. on the grid, and I_B = 60 mA. working into a 3 KOhm load yields 8.3 W. 3.2 KOhm is certainly close enough for the load. You could go the combination bias "route", with an unbypassed 330 Ohm resistor under the cathode and the rest of the bias voltage coming from a negative supply. The local current NFB (degeneration) associated with the unbypassed cathode resistor raises the effective plate resistance, which would mate nicely with that "extra" 200 Ohms. The improved linearity local NFB yields aids the cause too. __________________ Eli D.

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