Filter Cap Value

[DaveWell]

Hi !
For A Express New Built
I recently order some ARS Cap for the filter cap stack.
The thing is that I got 3 47Uf and 3 22Uf

I have no worries for the 22Uf,
But for the 47uf,
For the 2 first Filter cap connected together, is 2 47uF will be OK ou should i put a 33Uf and a 47uF ?

What is the impacy on the sound ?

Thanks for help and information you can give me !

Dave

[RJ Guitars]

Dave,
If you were to use the JJ can caps like some of us have done, you would parallel the two 50uF's to make it 100uF. Historically these amps sound really goood -- the Express I built with them actually sounds awesome, behaving like the text book Express (if such a thing exists).

I can also add another data point from actual measurements made on the NOS Mallory TC75 caps. I sent a handful of 47uF caps to David Root when he was interested in characterizing them. Among them was a NOS Mallory TC75. Much to my surprise this cap measured out above 47uF, well above the label value. This is only one data point but it gives you a hint that things are not always what they appear to be.

The design of the Wreck power supplies is intentionally very stiff. This has a subtlety to it that as a player you can hear and feel over a soft power supply. In this case you are talking about a subtle difference in the values that control this subtle property. There can potentially be other properties of a cap that also impact how this sounds and feels to the player so it's not entirely about uF numbers.

So, try it both ways and see if you can hear or feel it. My expectation is that if you are using high quality caps you'll like how it turns out with a pair of 47uF caps in parallel.
rj

[Roe]

I prefer 33uf at the screens instead of 47uf. For the mains 33+47uf works well. I use BC vishay 450v axials - highly recommended

[M Fowler]

I use 47uf-47uf on main filter and another 47uf on screens.

If I am using can caps I use 50uf-50uf on main filter and 40-20-20-20 can cap on remaining B+

[Colossal]

I prefer 33uf at the screens instead of 47uf. For the mains 33+47uf works well. I use BC vishay 450v axials - highly recommended

Hi Roe,

Those axial leaded Vishay/BC 450VDC caps are impossible to find here in the States The 100V and 250V 118 and 138 series are available, but all the big ones are now screw-in or snap-in only. Even then, most of them are listed as Non-Stocked by the big supply houses.

[Roe]

you can find them on ebay

[R.G.]

Electrolytic capacitor values are very often not close to the nominal value. That is because the capacitance varies with the thickness of the insulating layer, and that varies with the forming voltage, and that varies over the lifetime of the cap.

Electros used to have tolerances of as bad as +80%, -20%. The manufacturers knew that over the lifetime of the cap, the oxide would get thinner and so the capacitance would go up, but the voltage it will >really< tolerate will go down. So the "capacitance" on the label is a goal, not a promise.