HexFred diodes for Luxman MB3045

[tutor_turtle]

Has anyone modified their MB3045 with Hexfred diodes?
Looking at VS-HFA08TB60HN3

I just repaired a Cary tube amp, they used two in-series.
Do I need to series two?

 

[gadget73]

usually diodes in series are to deal with limited PIV values. Datasheet on this one lists it as VR, which I assume means voltage reverse. Same thing. 600 volts. A 1N4007 for example is good for 1000 volts.

so yes you probably do need 2 in series but see what the stock diodes are and confirm their rating. You may need 3, I don't happen to remember the power supply config in these.

or leave the stock diodes if they aren't causing you trouble.

 

[tutor_turtle]

usually diodes in series are to deal with limited PIV values. Datasheet on this one lists it as VR, which I assume means voltage reverse. Same thing. 600 volts. A 1N4007 for example is good for 1000 volts.

so yes you probably do need 2 in series but see what the stock diodes are and confirm their rating. You may need 3, I don't happen to remember the power supply config in these.

or leave the stock diodes if they aren't causing you trouble.

No problems that I know of....
I'm always looking for little tweaks that may incrementally reduce noise etc.
I am an old school tech (retired after 50+ years) I love to tinker, roll tubes.

 

[kward]

HexFred diodes would be a good upgrade for a 70's amp, in my opinion. If you can find a 1000V PIV (VR) HexFred version you would probably not need to apply them in series, but it depends on the secondary voltage used on the power transformer on that particular amplifier and how the rectification is performed. (full wave bridge, full wave center tapped, etc).

 

[Blue Shadow]

but it depends on the secondary voltage used on the power transformer on that particular amplifier and how the rectification is performed. (full wave bridge, full wave center tapped, etc).

Maybe this will answer some questions

 

[Tom Bavis]

For the full-wave rectifier, 600V diodes would be marginal - works out to 1088V reverse split across two 600V diodes, and that's not allowing for any imbalance or higher voltage at turn-on. UF4007s would give some margin.

 

[gadget73]

I meant to post yesterday, had it half typed and got distracted. 385v * 2.828 will give you the peak to peak voltage from the schematic's RMS voltage, which also happens to end up being the reverse voltage it needs to handle. One diode definitely not enough, and I agree two is pretty marginal.