Looking for info on filter capacitors

[Alley_Cat_Jack]

I am working on designing my first tube amp. I have a transformer and a tube rectifier that should be suitable for the amp. What I don't know is how to go about picking what filter caps to use. Was wondering if anyone knows of any good resources for determining size for filter caps as well as the resistors that accompany them.

[Zozobra]

The Valve Wizard

That should get you started.

[mozz]

The tube datasheet would have the maximum size filter capacitor for that particular tube. Also, the resistors that come after them are determined buy what voltages you want at the other nodes.

[stokes]

I wouldnt put much stock in the listed input capacitance in tube data sheets.I have 2 amps I built with 5R4 rectifiers.The data sheets say 4uf for the cap.I have been using 80uf for years with no problems.Also the 5v4 lists 10uf have been using 40uf and better.

[Alley_Cat_Jack]

The Valve Wizard

That should get you started.

Ahh perfect. Exactly what I was looking for. Thanks.

[mozz]

I wouldnt put much stock in the listed input capacitance in tube data sheets.I have 2 amps I built with 5R4 rectifiers.The data sheets say 4uf for the cap.I have been using 80uf for years with no problems.Also the 5v4 lists 10uf have been using 40uf and better.

5R4 There is a data sheet that says 20uf. maybe it was GE? Anyway, that usually says typical usage and it was at 20,000 or 40,000ft. The 5V4 does say 10uf, but typical again but also on the bottom is says capacitance may be increased as long as the peak plate current is not exceeded, which is 525ma.

They are both good rectifiers, but anyone designing or building their very first guitar tube amp should kind of stick with common or known good rectifiers such as 5y3, 5ar4 or 5u4gb. There are also many who think solid state diodes are great (they do have their places) and tube rectifiers are useless today, me, not so much.

[Alley_Cat_Jack]

I have a 5V4G that I am likely to use. I am going with the tube rectifier because of sag. I saw somewhere that someone said that single ended power amps wont experience sag, but I am thinking of going with paired EL84's.

[Chuck H]

A simple circuit for avoiding excess capacitance right off the rectifier tube is just another capacitor and a 100R resistor. Just stick to the spec value off the rectifier, then the 100R, hang a bigger cap off that and use it as your first node. The rectifier charges the smaller cap safely and the bigger cap charge time is limited by the 100R. There is very little sag in this circuit, really. Maybe 10V +/- depending on current. But the ripple rejection is improved enormously. I'd really recommend doing this with a 5V4 because they don't sag a lot anyway (so another 10V is ok) and tend toward a lower capacitance spec.