Filmosound / Spitfire Conversion Amp Project Questions

[taskforce]

Hello all,

I'm working on a fun little project using a vintage Filmosound amp chassis/transformers to build a Spitfire clone with some tweaked values. I'm a huge Matchless fan (own an actual Lightning Reverb), and I'd like to use the Spitfire base for my conversion with some changes.

-First of all, I do not wish to use a master volume, is it okay to simply clip it out of the circuit?

-I was going to change the PI plate resistors from 100K to 470K, will this work out okay? From my understanding it will produce more gain in the PI section?

-Was also going to change the coupling caps on the PI to 0.1uF similar to a 5E3, are there any other changes to make when doing so?

-Splitting the cathode on the input stage to some Marshall-y values that I've used in my Plexi mods I've done.

-Would adding a negative feedback resistor kill the vibe of this amp? I'm torn because I'm a fan of amps that have it and also don't have it. Thoughts?

Any advice would be appreciated.

Here is the Watts layout I'm adapting to.
[img:4513:3450]http://www.tubeamplifierparts.com/layou ... layout.jpg[/img]

Thanks!

[M Fowler]

Yes just eliminate the MV wiring.

Can go with Marshall value 470K/470K rather then 220k/220k keep 100k/100k and you may want to reduce the PI bias resistor 1k2 down some to 820R less treble.

1M/1M to 470k/470k, 820R bias, 47k tail resistor in PI

1k5 grids to 8k2 on the power tubes

Dartanion made a nice little 18w layout EF86 lite I like

[taskforce]

Thanks for the reply!

Just wondering with playing with those grid resistors would do. Am I going to lose a ton of top end by upping them to 8.2k? How about somewhere in the middle, 4.7k maybe? If I left them at 1.5k, would I have issues after changing the other values?

[M Fowler]

It will depend on how bad the amp fizz gets. You might be just fine with 1k5 these EL84 based amps need tweaking to get right.