Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Quickie => Topic started by: karl on June 30, 2012, 10:37:38 AM

Title: 3S4 Lineararity
Post by: karl on June 30, 2012, 10:37:38 AM

How linear is the 3S4 in the Quickie?

BTW, why is the filament powered at 1.5V and not 3V?

Regards,

Karl

Title: Re: 3S4 Lineararity
Post by: Paul Birkeland on July 02, 2012, 11:09:07 AM

Hello Karl,

Here is a datasheet with triode curves: http://www.mif.pg.gda.pl/homepages/frank/sheets/137/3/3S4.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/137/3/3S4.pdf)

Because the 3S4 is a directly heated triode, and we prefer cathode bias over fixed bias, each tube requires its own independent filament supply. Within the design of the 3S4, the filament is center tapped to allow for either 1.5V or 3.0V filament power (much like the heaters on the 12AU7, which we power with 6.3v). Consequently, it was sensible to use a pair of 1.5v cells instead of four 1.5v cells to make 3V, or one of the other expensive 3V batteries floating around.

Rest assured, you could design a similar preamp with two 3v supplies if necessary.

-PB

Title: Re: 3S4 Lineararity
Post by: Paul Joppa on July 03, 2012, 04:48:18 AM

In fact, seeing those curves was the inspiration for the Quickie. They are unusually linear.

Title: Re: 3S4 Lineararity
Post by: karl on July 03, 2012, 05:15:36 AM

Thanks, PB and Paul.

BTW, I need, surprisingly, some gain after my DVD/CD player and before my swichting amp. I hope the Quickie fits the bill.

Regards,

Karl