Russian K40-Y Caps Recommended Value

So I read often on the recommendation to try the Russian K40-Y capacitors for the Dynaco amps. It provides a good bang for the buck. I do see that the voltage rating should be no less than 400 volts and to give it around 200 hours of break-in time. However, very few instances in the postings are recommended values for the cap. Specifically for the Mark III with the upgraded VTA board what specific value of the K40s are recommended? 0.33? 0.22?

Thanks

The oil is almost like a thin grease .. It's thick ...


KY jelly?   

Thank you Bob for elaborating.

"You can really use any cap between .10 uF to .33 uF and not hear any difference in the sound of the amp"

When in doubt split the difference......0.22uF.

You don't want to go too low on capacitance...if you limit the low frequency bandwidth so that some frequencies do not pass, the result will be a large feedback signal to the first stage, in an attempt to correct the roll-off. Not good.

Some say larger-value capacitors don't sound as good, all other things being equal. However, since those "other things" are seldom equal, it's hard to judge the truth of this claim.

"You don't want to go too low on capacitance"

You shouldn't go too high a value either as you don't want to pass near DC voltages that take a long time to settle due to the added capacitance.  This "blocking" distortion can throw off the DC bias until the voltage bleeds.  0.22uF are good values to try.

BNR_1 wrote:So I read often on the recommendation to try the Russian K40-Y capacitors for the Dynaco amps.    However, very few instances in the postings are recommended values for the cap.  Specifically for the Mark III with the upgraded VTA board what specific value of the K40s are recommended?

Let's assume that the circuit designer was competent, knew the math, and had the equipment to measure the amp's output.  What's wrong with using the original values?  You certainly do not want to go below the design voltage (irrespective of the part's actual voltage rating) just as a matter of safety, and wandering too far from the capacitor's value (uF) risks throwing off the circuit operating parameters.  Diddle too much with some capacitor values and you end up with an expensive oscillator.  Or a dead rectifier tube.  Is there truly any realism added to the music by being able to amplify record warps?

I vote for staying pretty close to the designer's value, whether it be on the original Dynaco input board or the VTA (or any other brand) upgrade board.

Just my two cents.

Thanks Darth. You do bring up valid points. This is why I asked these questions. I have no experience whatsoever as to the recommended capacitor values and seek feedback with others that do.

"I have no experience whatsoever as to the recommended capacitor values and seek feedback with others that do."

What is the standard value for the VTA board? I would just use that value.