5T4 sub for 5Y3 ?

[HaroldBrooks]

Looking for a higher capacitance handling rectifier, and I came across this one :

https://frank.pocnet.net/sheets/127/5/5T4.pdf

Something like a 5U4 ( I think ) but only 2A filament draw.

Can I use this in place of a 5Y3 ? I would like to be able to run a higher (40uf) first filter cap off the rectifier without adding any additional resistance of voltage drops.

Thank for the help !

[mozz]

5ar4 is what you want. That being said, 5t4 is gonna be hard to find anyway. Data sheet says to add resistance when you go about 40uf, so in that case just use a 5y3 with a resistor then a big cap.
A 47uf on a 5y3 won't kill it instantly, they are pretty common and old USA made tubes are easy to find.

[Chuck H]

5ar4 is what you want. That being said, 5t4 is gonna be hard to find anyway. Data sheet says to add resistance when you go about 40uf, so in that case just use a 5y3 with a resistor then a big cap.
A 47uf on a 5y3 won't kill it instantly, they are pretty common and old USA made tubes are easy to find.

This^^^^^^^^^^^^^^^^^

Except that a 5ar4 is going to have a lot less voltage drop. A larger change (voltage going up) than you would get using a pi filter arrangement (voltage going down).

The pi filter also has the benefit of more filtering, lower ripple than simply bumping the uf's.

[Justin Thomas]

Bazillions of Champs & Vibro-Champs have been running for decades reliably with a 40μF filter cap on a 5Y3. Look into a tR4 maybe, too. Drops more voltage than a 5AR4 but has better PIV & current ratings.

Justin

[HaroldBrooks]

Thanks for everyone's input !

Chuck, I am just getting started with this. What is a PI filter ? I don't mind bumping up the voltage a bit in this particular amp as I have all new caps and they are rated to 500V, and the B+ currently is right around 383vdc, so there is some cushion. Also, could I use the PI arrangement with the 5AR4 tube ? The main goal here is to reduce ripple, so if what I am saying doesn't make sense, please feel free to point it out.

As always, thanks for the help !

[Chuck H]

A pi filter has nothing to do with pi outside of it's appearance, which when drawn in some schematics looks vaguely similar to the symbol for pi.

A pi filter would be a filter capacitor to ground, then a resistor and then another capacitor to ground that acts as your circuits voltage supply. You will lose very little voltage with this arrangement. Less than if you just used a resistor for certain. And this arrangement allows you to show a smaller capacitance to the 5y3 and then follow with a resistor that insulates the rectifier tube from inrush current to the larger, downstream capacitance. I guess it's enough to protect the rectifier tube, though I don't entirely understand how since the sag and voltage drop from a modest pi filter are really negligible. There's still plenty of tech that's beyond my skill set. Anyhoo... Here's a champ I did not long ago. The user wanted something very different from stock. Notice the 5y3 "see's" the standard 20uf cap, then there's a 100r resistor and then the 47uf cap I'm using as the first power supply node. This is a pi filter.

[HaroldBrooks]

Fantastic !

Thanks for your expert tutorial. I will try this out for certain, and forsake the rest. Looks like an elegant way to 'trick' the power supply node and save the rectifier from the torrent.

I have to get off this "I'm using a Big Filter Cap" obsession LOL. Better ways to tackle that I see.