20/10/10 cap can for Supro 1624

[oc disorder]

Two years later...Any postscripts/conclusions to this Tone Meister and Gingertube ?

"Well, nothing like a real-world test to see what is and what is not fact. The Supro here has 10 uF on the screens and Gingertube has one with 22 uF on the screens. If the advice I received is accurate, it shouldn't be too awful long before the tubes self destruct in his amp. Otherwise, it's much ado about nothing."

I guess it's too small a sample to be of any significance.

[Gingertube]

The unit I restored with 22uF on the screens is going strong. No issues since the restoration was completed Feb 2014. So I conclude that there is no significant issue with the 22uF screen supply filter cap in lieu of the 10uF.
Cheers,
Ian

[Tone Meister]

I limited the amp I worked on to 10 uF on the screens, so nothing meaningful to report.

[oc disorder]

Ok so it goes in the " it's much ado about nothing" basket !

It seems both your values were still in the ball park.

From EL34 world
"In a nutshell: low supply R and high voltage => low capacitance, say up to 20µF for a real 5Y3GT; highish supply R and medium voltages => higher capacitance, say up to 47µF or so. Anything between 16 and 33µF is usually safe."

From AX84
Exceding the max value will shorten the life of the tube. Use any value you like, but accept you will have to change rectifiers more often if you go bigger

When the amp is first switched on, the 5Y3 sees that first cap as an empty container to fill (almost like a short to ground). The tube charges the cap at maximum (the PT and 5Y3 are pulse-charging the first cap at this point). If that first cap value is too large, it will stress the 5Y3. The values of later filter caps are less critical, because the chokes, resistors and other components in the PS filter section buffer the current rush.

[Gingertube]

So the "Penny" Drops - thanks OCD
They are not talking about eating output tubes but rather eating the 5Y3 rectifier.
Max Cap for 5Y3 is 32uF (From data sheet). On the1624 the first cap is 22uF and then there is a 1K to the screen cap. That 1K will suppress (to some degree) initial charge current in the screen supply cap so either 10uF or 22uF will be fine in that position.
Just make sure to NOT increase that first 22uF cap.

Cheers,
Ian