A question about diodes...

[mr mojo]

Hello!

I'm using two rectifier diodes-one off each of the HV secondary leads, capacitor/resistor shunt and two 50k IIRC 10 turn wirewound pots with electrolytics grounded positive for bias. I've read this isn't the best set-up, but this is my first DIY and I didn't want to stray from the schematic.

Circuit shows, IIRC, .25 amp 600v selenium diodes-it's an old circuit.

I was wondering if using 3 amp 1000v silicon diodes would cause any problems. I've got 800vct on the HV secondaries and need @ -20v per side.

I've got the 3 amp 1000v silicon diodes on hand, and I like the idea of over-rating for less heat and greater longevity, but I don't know if using the larger diodes will lower the voltage significantly.

Any and all help would be appreciated,

mr. mojo

[leadbelly]

Originally posted by mr mojo
but I don't know if using the larger diodes will lower the voltage significantly.

No, not at all.

Use them, they will work well.

[Sch3mat1c]

Wadaminit, for BIAS SUPPLY!? You can use fraggin' signal diodes...well if they'd handle the voltage. Even for a hearty 250mA B+ the old 1N4007 is still FOUR times overrated.

Tim

[mr mojo]

I know replacing a selenium rectifier with a new silicon rectifier will result in lower voltage due to higher efficiency-but I always used over-rated bridge rectifiers in the Scotts I restored and didn't know if the efficiency difference was due to silicon vs. selenium or the higher voltage/current capacity.

I know it's way overkill-but I've got 'em on hand and it saves me a trip across town and the heartburn of dealing with our local electronics distributor.

Thanks for the help guys-I do appreciate it!

mr. mojo

[Sch3mat1c]

Nah, it's the semiconductor. One thing you'll notice about big diodes is they have basically the exact same characteristics as a 1N4007, but because the current runs higher, they actually have more voltage drop. 1N4007 is something like 0.8V at 1A; 1N5408 is like 1V @ 3A, and stud rectifiers well I don't have data offhand. For the same current, bigger diodes are slightly better, due to the larger junction, but you'll notice the pocketbook hit long before you see any difference in efficiency between other silicon diodes. Unless you use free or junk diodes, in which case I'll all for reusing parts.

Tim