Rectifier question

[zapped]

I have a power trans. with 340-0-340v. wired to a 6x5 rectifier tube, the dcv out of tube is 308 there are no caps installed I was trying to test the tube and trans,. does the voltage seen low???Thanks

[38Super]

Without filter caps, there is still a large amount of AC on the rectifier output.  If your circuit is wired correctly and you add a filter cap, you should see expected DC supply voltage.  Output of FW rectifier is 120Hz AC + DC.  Addition of filter caps smooth out the AC signal riding on top of DC voltage.

cheers,


rob

[RicharD]

As noted, you need some filtering to get rid of AC ripple.  You should expect to see 374VDC.  Stick a 50uF/450V cap on there and load it with a 220k resistor so it will eventually drain when switched off.

[firemedic]

That cheat sheet is great, thanks buttery!

[zapped]

Thanks for the help. I did not have a 50mf cap on hand but i tried it with a 20 which gave me about 430v. unloaded. Will that voltage change much with other value caps if used in a treew deluxe type of build ?? Butterylicious thanks for posting the cheat sheet...           regards  Ed

[jjasilli]

Whoa, max input filter cap value for a 6X5 is only 4uF.

[zapped]

The original schem. for the unit this transformer was removed from had a 25uf/450v and listed 375-415vdc off that Cap., so with todays line voltage 440 should be about right. I may use it for a tweed deluxe type build, would 440v be too high for a pair of 6v6's. I should assume the voltage will be pulled down some with the full compliment of tubes. This trans used to power a 6sc7, a 6sl7, a 6sn7, a 6k6, a 6e5, and the 6x5 rectifier. Could it do a princton reverb style????  Thanks

[RicharD]

Whoa, max input filter cap value for a 6X5 is only 4uF.

I read that as typical.  22uF should be fine.  My previous 50uF might be a bit much.

[zapped]

So is it the specs. of the rectifier and voltage output for the PT that dictate what the filter capacitors should be???and should i stay with the 25uf/450v. even if i were to try to go with a tweed deluxe type circuit???? Thanks again...  Ed

[ThermionicEngine]

The first stage of filtering is the one that has the most impact on the rectifier.  If you use a 5E3 circuit, first cap is 16uF @450, which should work fine.  The Specs for operating characteristics of the tube goes like this- input 325VAC RMS (measured without load) each plate with input filter cap of 10uF results in 450VDC at cap input. So your measurements sound okay to me. 

Good luck,
Larry