Input filter cap value 5V4

[lowell]

I'm designing a power supply 460-0-460 w/ 5V4 rectifier tube. The data sheets says that typical value here is 10uf for capacitive input. What if I'm using a choke pi filter? I want to do 16uf-choke_16uf. Will the first cap need to be changed to 10uf? EG 10uf-choke_16uf?

[tubeswell]

Nah it should easily handle 16 if it handles 10.

BTW the 5V4 datasheet says 10uF, but the 5V4G says 60uF - which one have you got?

If you're worried about it, put a 1N4007 on the HT winding in series with each anode. That'll protect the PT if the tube shorts

[Enzo]

That first cap is what the tube sees. The fact you have a choke after it won;t diminish the size of the cap as far as the tube cares.

[lowell]

Ok guys thanks for that. Not sure if I'll be using the 'G' version or not. Tubeswell, does the anode go towards the winding and the cathode towards the tube plates? Also, does this affect the rectifier function in any way, especially the sag factor?

[GibsonLover]

I had a GZ34 question today, and this is a quick reference of all the good ones

[tubeswell]

Tubeswell, does the anode go towards the winding and the cathode towards the tube plates? Also, does this affect the rectifier function in any way, especially the sag factor?

Anode (band) goes towards the plate. It doesn't affect the rectifier function in any way whatsoever. The tube will sag same as always. FWIW I've gone to doing this on all my tube-rectified amps

[unparalleled]

Radiomuseum.org

I'm designing a power supply 460-0-460 w/ 5V4 rectifier tube. The data sheets says that typical value here is 10uf for capacitive input. What if I'm using a choke pi filter? I want to do 16uf-choke_16uf. Will the first cap need to be changed to 10uf? EG 10uf-choke_16uf?

I use this site as a reference:

5V4, Tube 5V4; Röhre 5V4 (5V4)

[lowell]

ok that's good info. tubeswell, I'm thinking that the 1n4007 will open if current surpases the 1000ma PIV? Is that how they protect the ot?

[tubeswell]

Its not so much that the diodes will open, as that if the tube shorts, then it won't destroy the PT, because it won't hurt the diode if there is a 5V winding connected at the diode's anode end.

[lowell]

Ok hmmm... so I'm trying to grasp this. Lets say the HT is 460-0-460 and then there's the 5V rect winding AND the tube is a dead short. So 5VAC on the anode side and 460VAC on the cathode side. I'm trying to understand this and correct me if I'm looking at it wrong. When the HT is swinging negative the 5V winding must also be, right? So the two windings are in tandom frequency-wise but obviously the HT is larger peak to peak. So this being the case, the 1N4007s are never forward biased. They just act as a buffer b/t eachother when the tube is shorted. I'm also assuming that the rectifier plates seeing pulsating DC is not a problem. The rectifier tube only conducts the positive half of the signal even when it sees AC? This'd make sense as the tube's name infers.

[tubeswell]

When a rectifier tube shorts and dumps high voltage AC power into the filter caps, the caps fail, and if they short, then this shorts the HT winding (because the rectifier tube is shorted). The diodes prevent this

[lowell]

Ok yeah so it's basically a "backup" rectifier in case the tube shorts. What I'm not totally clear on is how these diodes are only letting the negative pulsating DC through, and the rectifier tubes still functions the same. Is that the case? And if so, how does the tube flip that to positive pulsating DC?

[tubeswell]

Ok yeah so it's basically a "backup" rectifier in case the tube shorts. What I'm not totally clear on is how these diodes are only letting the negative pulsating DC through, and the rectifier tubes still functions the same. Is that the case? And if so, how does the tube flip that to positive pulsating DC?

Each diode is letting the +ve cycle through (the diode anodes are pointing away from the HT winding). The voltage drop is virtually nil, so the tube rectifier is seeing almost the same +ve swing that it would see if there were no diodes there.

[lowell]

The band is the cathode and the anode goes to the HT...? I think that's what you mean. In your first reply here you said the anode was the band. Ok I get it, thanks!

[JoeM]

The band is the cathode and the anode goes to the HT...? I think that's what you mean. In your first reply here you said the anode was the band. Ok I get it, thanks!

Yeah, the banded side is the cathode. Anode to the HT (same direction as the tube).

R.G. Keen has a good article on this:

The Immortal Amplifier Mod - Premier Guitar