For the sake of learning ! Germanium vs Schottky Diodes

[whiteastro]

I keep thinking about improving the receive on my DX 2547 and have been told Germanium is better than Schottky as far as the diode replacement goes so I thought this might create a interesting discussion amongst the experienced repair techs. I figure it is better to make all my mistakes on paper before I make them in my wallet. And yes I have been told that it will bring in more noise also but I'm counting on my West Mountain Radio noise filter to help me out in that department. I look at it as The majority Wins ! Fight Nice ! LOL

 

[brandon7861]

Germanium have more reverse leakage than shottky, but I havent figured out the implications of that for given circuits yet.

Comparing the turn on curve of the germanium 1N60 to shottky diodes like the BAT46 and the 1N5711, the germanium passes much more current for a given value of Vf. At .4v, the 1N60 is passing about 40mA whereas the BAT46 is passing about 9mA and the 1N5711 passes just over 1mA. If all you have is .2V to forward bias the diodes, the 1N60 might pass a mA or two, whereas the shottky diodes will be passing mere uA's. If I had to choose between the BAT46 and the 1N5711, I'd probably take the BAT46 as it is much closer to the 1N60 than the 1N5711.

If someone knows of a shottky closer to the 1N60, I would love to know about it.

Luckily, I see the germaniums are still in stock over at RFParts, just ordered some. Germaniums are disappearing fast. I have a feeling that they will be impossible to find by 2030.

 

[whiteastro]

Luckily, I see the germaniums are still in stock over at RFParts, just ordered some. Germaniums are disappearing fast. I have a feeling that they will be impossible to find by 2030.

Thanks for the input of info because I have had no electronic training at all, just the bits and pieces I've picked up along the way. I wished I would have pushed myself to learn more earlier because it would have been a good retirement job setting at the bench and restoring some of these radios plus doing Mods. But you also have to have the manual dexterity for the small work. Every field has the technical side of it but it is nice just to learn it. Thanks again! I'm sure there is some out there that have tried them both and it would be nice if they tried each on the same radio.

 

[brandon7861]

I found a datasheet that shows the 1N60 and 1N60P together. I put those charts on the same page as the BAT42 shottky.

I was surprised to see the differences between the 1N60 and 1N60P. The 1N60P turns on at a lower forward voltage but has more capacitance and leakage than the 1N60. The BAT42 looks like it fits right between the two germanium diodes. In terms of continuous current handling, the BAT42 handles more than the BAT46 or the 1N60(P) parts. My last post mentioned the BAT46 because a forum mentioned using that as a replacement, but the BAT42 looks better. I wish I could look at datasheets all day.

 

[SuperLid]

I keep thinking about improving the receive on my DX 2547 and have been told Germanium is better than Schottky as far as the diode replacement goes so I thought this might create a interesting discussion amongst the experienced repair techs. I figure it is better to make all my mistakes on paper before I make them in my wallet. And yes I have been told that it will bring in more noise also but I'm counting on my West Mountain Radio noise filter to help me out in that department. I look at it as The majority Wins ! Fight Nice ! LOL

The main difference in this circuit is the forward voltage drop, which is slightly lower with a schottky. The original design used germanium,which cost more than schottky. Then the genius RX mods came around, that use schottky. I have found the germanium to work better and remove schottky's and install real 1N34's.