TW Express (or similar) with Parallel Triode Input

[PCollen]

Has anyone ever tried using a parallel 12AX7 input on an Express or similar build ? I hate to see a triode go to waste...

[Ken Moon]

Sure.

I think lots of folks have done this.

The Talon amp here is a tweaked Express preamp, with a cathode-biased, non-NFB 2x6V6 power amp, and an improved PSU. Here's the schematic so you can see the resistor/cap values around V1 (if you want V1 fully bypassed like on the Express, try between 33uF and 47uF for the cathode bypass cap):

[img808]http://moonguitaramps.com/images/talon_schematic.png[/img]

[guitarmike2107]

Yes I have done this, I found that you need to keep the first anode resistor at 56k or so , if you use 100k the gain is too much and you will spend days trying to perfect your lead dress.

[PCollen]

Yes I have done this, I found that you need to keep the first anode resistor at 56k or so , if you use 100k the gain is too much and you will spend days trying to perfect your lead dress.

As I posted recently to another thread, I got into my Dr. Z MAZ-18 once and noted the parallel 12AX7 V1 using (AIR) 68K on the anode and 1.2K on the cathode with a 22uF Ck bypass. 56K in the TW would likely be better than 68K, as you say, given the gain in the remeiner of the pre-amp.