BYV96D diode replacement in HD83?

[buddam]

Hello all

I've just dismantled a home-built HD83 I bought off ebay c.6 months ago. Full of Black Gates, Kiwames, etc. The builder seems to have added extra diodes as well as changing from the original BYV96Ds. There are 4 x 1N5820 and 4 x RHRP8120. The FAQ on diode choices mentions both these, but it is not clear to me whether they are replacements for the BYV96D

I'm going to rebuild along standard lines using the HD83 pcb. Would therefore be grateful for guidance on the diodes - which of these types are replacements for the BYV96Ds? I have the data sheets but don't know whether the the various measurements should be higher than those for BYV96D, the same, or lower?

Thanks

Adrian

[Richard]

Hi Adrian

The RHRP8120 will be replacements for the BYV96D for the HT bridge.

The 1N5820, at a guess, will be to convert the standard ac heating to dc. You may find a pi filter of cap, resistor (1-3ohms), and another cap, following that bridge, to smooth and set voltage.

[buddam]

Thanks Richard,

now you've mentioned the pi filter, I see that it's the other way round. The RHRP8120 were used just before those caps and a 3W resistor, feeding the valves. The 1N5820s must substitute for the BYV96Ds therefore.

Adrian

[Richard]

Hi Adrian

1N5820 are 20v schottkies so won't be for the HT. They aren't standard so my guess is someone's converted to dc heating and you'll find a cap-R-cap (or maybe just a cap) after them feeding the heaters.

The RHRP8120 are 1200v fast diodes and will be the HT diodes in place of the BYV96Ds. They feed that pi arrangement you mention as standard. (Apologies if I'm confusing you by trying to guess about the other set.)

[buddam]

Thanks again Richard. I can leave the 1N5820 out, but the RHRP8120 - I presume these are directional, but which way round? K is on the left as you look at the front, but does this correspond to the small shaded end of an axial diode a la BYV96D?

Thanks

adrian

[Richard]

Yes directional indeed, K = cathode and the marked end/band/shading of an axial is cathode.

Beware the metal mounting tag though as that too is cathode and will carry high voltage so mount clear and don't touch