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previous: Bruce Charles... Bruce here again,Yes... -- 9/9/1997 10:25 AM

Re: rectifier diodes

9/12/1997 4:54 PM
R.G.	Re: rectifier diodes Actually, there are two ways to do this, each with slightly different results. One is to put a single diode in series with each rectifier tube anode, the other is to connect the cathodes of the diodes to make a full wave rectified point, and then tie BOTH anodes of the rectifier tube to the cathodes of the SS rectifiers. In the first way, the tube rectifier acts as it normally would, alternate anodes conducting. In the second way (which is what I think you are talking about here) both anodes conduct every half cycle, effectively in parallel. The difference is that in the first case, the "plate resistance" of the tube rectifier is the same as it would be if there were no SS diodes there at all; in the second, since both halves of the rectifier tube are in parallel at all times, the effective internal resistance of the tube is halved. This will make some slight difference in the DC voltage and sound. The diode after the choke is a neat trick that stabilizes the power to the preamp stages; I saw that in the first issue of Glass Audio. On bypassing HV diodes, there are a couple of aims in doing that. In series strings, it does help to equalize the voltage distribution to keep from blowing the "weakest" diode first. In single diodes, though, it's a way of snubbing the turn off transient. As a diode turns off, it can reverse conduct for a very short time until all the carriers are swept out of the junction. This reverse conduction quits abruptly when all the carriers are gone, causing the diode to "snap off", a very abrupt change in current. This transient can literally be transmitted; it's a known source of EMI. The snubber helps that a lot. I've heard that the IR HexFRED diodes are very good for audio use because they have little or no snap off transients to get into the audio path.

9/12/1997 4:54 PM

R.G.

Re: rectifier diodes

Actually, there are two ways to do this, each with slightly different results. One is to put a single diode in series with each rectifier tube anode, the other is to connect the cathodes of the diodes to make a full wave rectified point, and then tie BOTH anodes of the rectifier tube to the cathodes of the SS rectifiers.

In the first way, the tube rectifier acts as it normally would, alternate anodes conducting. In the second way (which is what I think you are talking about here) both anodes conduct every half cycle, effectively in parallel. The difference is that in the first case, the "plate resistance" of the tube rectifier is the same as it would be if there were no SS diodes there at all; in the second, since both halves of the rectifier tube are in parallel at all times, the effective internal resistance of the tube is halved.

This will make some slight difference in the DC voltage and sound.

The diode after the choke is a neat trick that stabilizes the power to the preamp stages; I saw that in the first issue of Glass Audio.

On bypassing HV diodes, there are a couple of aims in doing that. In series strings, it does help to equalize the voltage distribution to keep from blowing the "weakest" diode first. In single diodes, though, it's a way of snubbing the turn off transient. As a diode turns off, it can reverse conduct for a very short time until all the carriers are swept out of the junction. This reverse conduction quits abruptly when all the carriers are gone, causing the diode to "snap off", a very abrupt change in current. This transient can literally be transmitted; it's a known source of EMI. The snubber helps that a lot.

I've heard that the IR HexFRED diodes are very good for audio use because they have little or no snap off transients to get into the audio path.

Replies:

Bruce I connected up to Microsemi and dow... -- 9/12/1997 8:23 PM
PAUL C I've seen these caps and resistors ... -- 9/12/1997 8:24 PM