Tube rectifiers

[razorrick1293]

Hello, ive got my new transformer now and i plan to build a parallel SE EL84 in triode mode, possibly pentode later on. anyway, ive got a free winding and thought i'd look into tube rectifiers since ive never considered them before. which one would suit a 225-0-225 @100mA with a 5v @ 3A rectifier winding?

Ricky

[6L6]

Any of the 5v rectifiers. 5U4 5R4 5AR4 will work well.

What B+ are you trying to get? Valve rectifiers have significant voltage drop vs. silicon.

[razorrick1293]

i was thniking of having both silicon and tube and switching between the 2. aiming for at least 280v HT at least, which shouldnt be a problem. what sort of voltage drop am i looking at? and will i only need the one or will i need 2 rectifiers?

[Eli Duttman]

The 5V4/GZ32 and 5Y3 will also be fine. The 5AR4/GZ34 has the lowest forward drop. The 5V4 has the next lowest drop, then the 5U4, then the 5R4, and the 5Y3 has the largest drop. The 5AR4, 5U4, and 5R4 are all rated for 250 mA. of B+. The 5V4 is rated for 175 mA. and the 5Y3 is rated for 125 mA. The 5AR4 and 5V4 have cathode sleeves and start slowly. The other 3 are directly heated and turn on almost as fast as SS diodes.

Check the data sheets for the I/P filter capacitance limits.

[6L6]

Without looking at my notes, a 5AR4 is 17v, 5U4 30-something, and 5R4 close to 60.

[razorrick1293]

thank you very much, this could be an interesting build

[razorrick1293]

by the way, i've heard tube rectifiers are very sensitive to filter caps? any values i should stick to?

[Gilgy]

Originally Posted by razorrick1293

by the way, i've heard tube rectifiers are very sensitive to filter caps? any values i should stick to?

Check on the data sheets for maximum values of filter cap

5U4 is around 47uF, some specify 33uF

[6L6]

Yes, good point. You CAN have too much filter cap on the first position of a CLC filter with a valve rectifier. As Gilgy said, check the datasheet to find the correct value.

I have had very good luck with 630v rated Solen caps in this position, they are awfully difficult to hurt.

[VictoriaGuy]

Originally Posted by razorrick1293

i was thniking of having both silicon and tube and switching between the 2. aiming for at least 280v HT at least, which shouldnt be a problem. what sort of voltage drop am i looking at? and will i only need the one or will i need 2 rectifiers?

If you don't already have Duncan Amps PSUD software, download a (free) copy. It's a good tool for answering questions like this.

Switching rectifier types is a bit tricky- if you want to have the same B+, you'll need some good-sized dropping resistors on your ss rectifier.