5R4 rectifiers

[Brownie]

I like to use the 5R4 to lower the B+ when the transformer may not be spot on for the circuit.  How much filtering on the reservoir is allowable with this tube. Am I to believe the tube data sheet and only use 20uF?   

[scstill]

Doesn't the 5r4y datasheet say 4uf
updated to 20uf if you have the 5r4yB

http://vinylsavor.blogspot.com/2020/08/tube-of-month-5r4.html

[bmccowan]

I have some 5R4s of various types - flea market box of rectifier tubes. It was a while ago, but it seems to me that most info I found stated that the filter rating was based on the tube running at full limit on the other specs, and that you could go beyond the filter rating at the conditions found in guitar amps. Caveat emptor, that's web surfing info, so I do know that I have used them with a 32uf reservoir. But I do not play very long or very loud.

[tubeswell]

20uF should be okay. (4uF was a standard reservoir cap size way back when, and conservatively rated on the data sheet to cover the tube manufacturer's arse against warranty claims). If you're concerned, wire in some 1000V 1A diodes in series between the PT High Tension winding ends and the plate pins of the rectifier tube as protection against the tube rectifier failing short. It won't affect the tube rectifier's 'performance' as you still get the tube's forward voltage drop.

[Brownie]

I do like those safety diodes on the back of the recto socket for sure.  I think I'll run the 5R4 into a 10uF cap, then a small Hammond "Deluxe Reverb" choke and then 32uF cap and run the B+ to the center tap.  Then a resistor and the Screen supply.  Does this sound feasible?  Thanks for the replies.

[tubeswell]

I think I'll run the 5R4 into a 10uF cap, then a small Hammond "Deluxe Reverb" choke and then 32uF cap and run the B+ to the center tap.  Then a resistor and the Screen supply.  Does this sound feasible? 

Depends what you're supplying. If its a little 5W SE amp with one 6V6 (or EL84) and a preamp tube or two, then yes a 40-50mA DR choke will have enough puff to keep up in a 'whole-of-supply' CLC filter (and such a CLC filter will be ideal for PS ripple cancellation in a SE amp)

[sluckey]

I do like those safety diodes on the back of the recto socket for sure.  I think I'll run the 5R4 into a 10uF cap, then a small Hammond "Deluxe Reverb" choke and then 32uF cap and run the B+ to the center tap.  Then a resistor and the Screen supply.  Does this sound feasible?  Thanks for the replies.

Sounds like a big mismatch. The 5R4 kinda implies big tube power amp. But the DR choke is only rated for 45mA. Using that choke as you described is barely big enough for a 5E1 Champ.

[tubeswell]

Also, see Note 2) on p1 for recommendation for reservoir cap larger than 4uF


https://frank.pocnet.net/sheets/201/5/5R4G.pdf

[Brownie]

Steve, do you suppose the larger "Fender" choke of 4Hy@90mA would be large enough for a 6V6 P-P like a Tremolux or 6V6 Plexi?  I may end up just going to 5U4 anyhow.  This 5R4 idea was just an attempt to lower the B+ back to vintage levels in the original Fender schematic.  Thanks everyone

[tubeswell]

5G9 tweed tremolux has a 40mA choke in a CLC filter between the OT plate supply and the screen supply node (input/reservoir cap on the plate side = 40uF). About 380V B+ with 300-0-300 HT and 5U4G tube. PS ripple is cancelled out in each half of the OT primary.


For a ‘whole of supply’ choke in a CLC filter in low power 5E4A tweed super (with 2 x PP 6V6), minimum of 90 mA rating. (Preferably 100mA), although if you follow the 5G9 logic, you can use the smaller 40mA choke.