Strange 5AR4 "Problem"

[jmaf]

What becomes of that difference when you put a tube after the diodes? This is what I'm missing and that's what concerns me. I don't want to end up with 500v on the plates os my power tubes.

Think of the tube rectifier as a resistor after the silicon diode. When you add a tube after the diode, it drops voltage, like every resistor does when there's current through it.

If you substitute a tube for a diode, and remove the tube, you remove that "virtual" resistor. When you put the tube in, that's how it "steals" voltage which I believe is your question?

[Diablo]

Thanks for both of your posts. Chucked the 5ar4. I'm going back to back to 5881's anyway. As for diodes in series with the rectifier plates, I'm not really worried about that. I have HT fuses to protect my transformers but in 30+ years of playing I've never had one fail. Adding diodes would just push my B+ too high for 5881's. There are times though when I'm gigging frequently that I'll stick a weber copper cap in an amp just to avoid the physical abuse to a $100 Mullard. But the advice is always appreciated.

I bought a used amp for cheap and it's main issue was that it would pop the fuse when you turned it on. It had a Mullard GZ34 that was shorted. It was likely an original rectifier tube in the fifty year old amp. Now it runs happily on a copper cap.

[Zer09]

That's the bit of information I needed. The tube resistance dominates the diode. All makes sense to me. It just sounded contrary to everything I've learned about rectifiers to this point. I'm actually going to go back and do it to all of my amps with tube rectifiers.

Now, when I did my first build, an ab763 deluxe reverb, I had a tech sort of guiding me through it via email support. he had me add 1.5kv, 1.5amp diodes in a similar manner with one on each plate. Would those be sufficient? I think I still have a bunch around but have plenty of 1n4007's as well. He was concerned about new production rectifiers and I hadn't started using Mullards yet. Like I said in the first post, I never had one fail but the peace of mind would be well worth the minimal effort. I'd be lying if I didn't say that rectifier tube failure has entered my mind at least once during every gig I've ever played.

[Diablo]

Now, when I did my first build, an ab763 deluxe reverb, I had a tech sort of guiding me through it via email support. he had me add 1.5kv, 1.5amp diodes in a similar manner with one on each plate. Would those be sufficient? I think I still have a bunch around but have plenty of 1n4007's as well. He was concerned about new production rectifiers and I hadn't started using Mullards yet. Like I said in the first post, I never had one fail but the peace of mind would be well worth the minimal effort. I'd be lying if I didn't say that rectifier tube failure has entered my mind at least once during every gig I've ever played.

Yes, one 1.5kv 1.5 amp diode on each plate should work fine as protection for tube rectifier shorts. If you run out of those diodes, you could use 1n4007 or 1n5408 (3-amp).