Tube rectifier to diode

[bereanbill]

Ok folks...time to coddl a newbie with a lot of dead brain cells...if you don't mind that is. I remember reading about using 2 IN4007 diodes on the rectifier socket to replace the rectifier tube, but I can't remember how it was done. I'm guessing the anode goes on the AC side of the socket and the cathode on the DC side?? Is this also the way to add surge protection with the rectifier tube in place ?? I'm thinking the voltage increase is about 20 volts versus a 5Y3 tube? Please correct me if I am wrong...and as usual, thanks for all the advice on my previous threads....

Afterthought...I have some 1000 volt, 1.5 amp diodes here...they would work not ? I think the IN4007 is 1000 volt, 1 amp ???

[kevinkr]

Correct on all except one count. To provide some additional protection for the rectifier tube you place the diodes in series with the plates, cathode end to rectifier plate.

The 1.5A 1KPIV diodes will work just fine.

[Miles Prower]

Originally posted by bereanbill
Ok folks...time to coddl a newbie with a lot of dead brain cells...if you don't mind that is. I remember reading about using 2 IN4007 diodes on the rectifier socket to replace the rectifier tube, but I can't remember how it was done. I'm guessing the anode goes on the AC side of the socket and the cathode on the DC side??

Yes, that's right. However, there are other issues with doing this. Replacing a hollow state diode with an Si diode will result in a significantly higher DC output voltage. The forward drop for an Si diode is about 0.7V, and doesn't rise much higher with increasing current. The forward drop for a hollow state diode is much higher.

In a project I did, I needed 350Vdc at about 100mA. In the junk box, I had a Stancor power xfmr rated at 650Vct @ 150mA. Looked good so far as current. However, connecting that to Si diodes gave a no-load voltage of 458V, and even under load, that didn't drop below 400V. It was either get a new xfmr, or include some sort of voltage dropper, or go with hollow state. A 5U4GB had just the forward drop I needed to get the DC where I needed it.

Is this also the way to add surge protection with the rectifier tube in place ?? I'm thinking the voltage increase is about 20 volts versus a 5Y3 tube? Please correct me if I am wrong...and as usual, thanks for all the advice on my previous threads....

Paralleling solid state and hollow state diodes doesn't work. The hollow state diode will have less than a volt across it, and will draw microamps.

Afterthought...I have some 1000 volt, 1.5 amp diodes here...they would work not ? I think the IN4007 is 1000 volt, 1 amp ???

If your PRV is high enough, the 1KV / 1.5A diodes will certainly work. Any reasonable DC ripple filter won't come close to its Isurge rating.

[bereanbill]

Thanks...I can always rely on you, Kevin and Miles. One other ?...is it safe to run a tube rectifier with the diodes in place? If so, what is the result...do I end up with the voltage drop accross the 5Y3 or the increased voltage of the diodes???
This is really beginning to be fun !!!
BTW...anyone following my first build...I replaced the OT with a higher output/quality one and the result was almost unbelieveable...output and sound quality improved remarkably !! Thanks for all your input everyone !!!!

[kevinkr]

Originally posted by bereanbill
Thanks...I can always rely on you, Kevin and Miles. One other ?...is it safe to run a tube rectifier with the diodes in place? If so, what is the result...do I end up with the voltage drop accross the 5Y3 or the increased voltage of the diodes???
This is really beginning to be fun !!!
BTW...anyone following my first build...I replaced the OT with a higher output/quality one and the result was almost unbelieveable...output and sound quality improved remarkably !! Thanks for all your input everyone !!!!

Yes it's safe to run them in parallel, however in this scenario because the forward drop of the silicon diodes is so much lower than the 5Y3 all of the load current will flow through the ss diodes and not the tube rectifier - the voltage drop experienced will be that of the SS diodes exclusively. Basically the 5Y3 becomes a decoration.. You can also configure things with a switch to select which one you want - at its simplest just tie the two ss diode cathodes together at a spst toggle switch rated to handle the voltage, and connect the other side of that switch to the cathode of your rectifier tube, voila switch open - tube rectified, switch closed < possibly small to not so small POP> and then the SS diodes take over.

[bereanbill]

Thanks again, Kevin...that was a question I wanted to ask as well. Would it be better to use an on-on switch...even though it would be harder to wire ? Would the pop be enough to damage a speaker ???

[bereanbill]

Next thought...these 1KVPIV diodes I have are rated at 20pf capacitence...is that any cause for concern ???

[kevinkr]

Originally posted by bereanbill
Next thought...these 1KVPIV diodes I have are rated at 20pf capacitence...is that any cause for concern ???

No, shouldn't be a problem..

[bereanbill]

Ok, I'm ready to do this alteration...I decided to use a switch to toggle between diode and tube rectifier. One ? ...what voltage rating do I need on the switch ?

[bereanbill]

Ok, Kevinkr's post on switching rectifier has me a bit confused...are the diodes installed with the anode of the diode to the anode of the tube ? That would make sense I guess...