Question re: rectifier diodes in Sunn 190L

[jhebass]

Just got done replacing most of the electrolytics in a Sunn 190L. Brought her up on a variac and she’s popping fuses. Haven’t had time to verify the integrity of my install, although it truly seems ok. That said, it obviously isn’t...

My question is that in the process I decided to replace the original pair of rectifier diodes with 4007s. The original diodes, “K416” type on the parts list, have a forward voltage of about 1.5V each. The new diodes obviously don’t. Is this problematic? Just seems weird!

[martin manning]

You might have a shorted diode. You will need diodes rated at a minimum for twice the 520V B+, and thrice would be better. 1N4007 are rated 1kV; so two in series would probably work fine.

[Stevem]

There's always a chance the a new filter is bad, ask me how I know this!

[tubeswell]

... The original diodes, “K416” type on the parts list, have a forward voltage of about 1.5V each. The new diodes obviously don’t. Is this problematic? ...

But 1N4007 only have a 0.6V forward voltage drop, so they are technically more efficient.

Forward voltage drop is a measure of the voltage across the anode and cathode when the diode is conducting forward current.

See: https://www.globalspec.com/learnmore/se ... _all_types

Forward voltage drop is not a critical parameter for the purposes of rectifying AC at the scale of voltages seen in a tube amp.

What's more critical, as Martin mentioned, is the Peak Inverse Voltage rating (For a 1N4007, this is 1kV) and the maximum forward current rating (1A in a 1N4007). The need for having sufficient current handling is obvious and you simply add up the current draw that the load is comprised of in order to work out what rating you need.

For any required PIV rating (i.e. if you don't know what the rating of a K416 is), you can work out what you need by factoring in the rms voltage across the HT winding and the type of rectifier that the circuit is using (i.e. FW Bridge, 2-Phase, 1/2-wave etc).

Useful article for reading about PIV for guitar amp rectifiers: http://www.valvewizard.co.uk/bridge.html

[sluckey]

I would not be surprised if that "K416" diode was really two diodes in the same plastic container. That would explain the 1.5V forward drop.

[jhebass]

Thanks all. Interesting point re: the K416 really being two diodes.

I’ll experiment further and report back.