Tweedle Dee Deluxe electrolytics Q

[Oddvar R]

Hi. I am thinking about building a TD Deluxe- I have a lot of leftover parts from previous builds. I see there are 33uf's in that build, and I am wondering what significance sound wise the UF has since there a a lot of difference values in different amps. What would be the difference between 25/25 vs 47/50 in the V1 bypass? And 33uf vs 47 or 22uf in the filter section?

[erwin_ve]

For the triode gain stages, cathode caps define the frequency knee. The larger the bypass cap the lower the frequency that will be amplified. And vice versa.
For the power supply filtering: a 33uF or 47uF is not going the be a massive change in sound but will affect the feel of the amp as larger Ps caps dont have the compression(in the feel of the amp) of a smaller ps filter cap.

I recommend you take a look at valve wizard, there are some great explanations how these things work which maybe are too big to post here.
http://www.valvewizard.co.uk/gainstage.html

[martin manning]

For the triode gain stages, cathode caps define the frequency knee. The larger the bypass cap the lower the frequency that will be amplified. And vice versa.

In part, but there is more to it. Doubling the bypass capacitor will lower the frequency of the Rk-Ck roll-off by half, but there is a point beyond which it doesn't matter much. A 22u bypassing the typical 100k Ra, 1k5 Rk 12AX7 stage is said to be "fully bypassed," as the -3dB frequency is at about 10Hz. The low frequency roll-off due to the coupling capacitor and the load following it is also around that frequency range, and in the Deluxe it will depend upon where the volume and tone controls are set. The short answer is go ahead and use the 47u. The Rk bypass capacitor is much more of a player when its value is in the 1-10u range.

[Oddvar R]

So I have two Rifa 33uf, 450v, and one F&T 32-32 uf 500v. Would they be combinable?

[martin manning]

Sure. I think I would use the 32-32 for the plate and screen since they share a common ground.