IRF140 power mosfets

[diy student]

While looking back through "The Return of Zen" I noticed that Pass makes a comment about how much more he prefers the IRF040 and the IRF140 than the IRF240. He also states that as you go from the 040 to the 140 distortion increases by 50%, and as you go from the140 to the 240 it increases to 100%. The 040 is discontinued, but the 140 is still out there. What's more I can't find the 240 for as cheap as I can the 140, but Pass warns of a shortened life for the amp if the 140's are used. I don't know very much about circuitry (thanks for putting up with me guys), but I'd imagine it's because the 140 has a rating of 40V. I was wondering if the 140 could be used for some of the smaller Aleph models? Specifically the Aleph 3 and Aleph 5. What kind of change in lifespan might the amp be looking at, and if a MOSFET did go on an Aleph what else if anything might it destroy? Thanks in advance for any input.

Rob

 

[GRollins]

Rob,
The key to this is the specs, in particular the SOA chart of the spec sheet. Go to http://www.irf.com and look up the IRF140. It will come up as a PDF file. The SOA chart is on page 4.
The Alephs vary in how much current and voltage they apply to the output devices, but the power dissipation (per device) always ends up in the 22-25W range. The IRF140 is a 125W device, which leaves you a little elbow room. It then boils down to the particular ratio of voltage and current Nelson used in that Aleph. By all means, check the chart and calculate the wattage for your chosen circuit. You will probably find that it will work.

Grey

 

[Petter]

Zen is a one-stage design. Transistors with higher current gain will probably yield better results in that setting.

Petter

 

[Nelson Pass]

I don't recall warning about a shortened life span
for the 140's or 040's per se. The comments were
about running any of these devices at much higher
bias currents, so use the 040's or 140's if you
can get them.

 

[diy student]

Thanks so much for the feedback. I found the transistors I priced may have been the 1404's and 1405's, but I'm going to see if I can find a place to pick up some 140's. Your advice truly is invaluable. Thanks for your time.

Rob

 

[promitheus]

The 040´s are hard to find. Mostly I find the 240 and 250´s.
If you find the 140´s go for it. They are very good.