Transistor alternatives and replacements (Pro-Electron, EECA, JESD370b)

[Cicada]

Hi

I have to recreate an very old plugin card in a power supply. There are some transistors which I cannot source anymore. For example Motorola BU205

Then there are some transistors like the Texas Instruments 2N4240 for which I can source the same part number from other manufacturers. https://octopart.com/search?q=2N4240&currency=USD&specs=0
Click on the Manufacturers button to see (NJS, RCA, Microchip, Solid State Manufacturing)

All these devices are named according to these naming standards "Pro-Electron a.k.a. EECA" or "JESD370b".
This article describes the standards and gives a quick overview how the transistor codes are derived. https://www.electronics-notes.com/articles/electronic_components/transistor/transistor-codes-numbering.php

Now my questions.
1. For the BU205 I will have to look for alternatives. Is there a online database of alternatives, website, app or any tool of any kind that can make this easier than comparing datasheets? Maybe even a paid service?
2. For the 2N4240 I will have to buy a device from a manufacturer other than Texas I. Does devices with the same name have to have comparable/compatible specs? I.e. are these devices interchangeable

Cicada

[Terry Bites]

These transitors abound on ebay at low prices. But make sure you test them first

[Cicada]

Relevant JEDEC documents can be downloaded from www.jedec.org free of charge after registration.

UNDERSTANDING DATASHEETS
JESD10.pdf
This standard define terminology and test methods for the transistor parameters listed in a typical datasheet. This is a great aid to understand transistor datasheets to identify alternatives.
The index of this doc:
1.
2.
3. Verfication tests
   3.1 Maximum ratings
   3.2 Safe Operating Conditions
   3.3 Electrcal Characteristics Tests
4. Thermal Characteristics
5.
6.

JESD10 refer to https://www.jedec.org/committees/jc-25

You can also look at JESD77D


TRANSISTOR NAMING CONVENTIONS
JESD370b can also be downloaded from the Jedec site.

EDIT. Sorry if this bump this post up again. I just wanted to add this link for my future reference.
https://www.jedec.org/standards-documents/focus/registered-outlines-jep95/transistor-outlines-archive

[BrokenYugo]

I don't think any slow 1500V BJTs are still in production, especially in TO-3, so that one will have to be NOS.

The whole point of part numbers is they're supposed to be interchangeable, compare datasheets (good idea to grab a period correct one) to confirm. There are some exceptions like the 2N3055, but that's a special case of a very early and poorly specified part that ended up having a very long life.

[pardo-bsso]

Look into the NTE catalog for equivalences.

Also in some places (like my country) you can buy NOS over the counter.

[kripton2035]

245 equivalents to the bu205 here :

https://alltransistors.com/crsearch.php?mat=Si&struct=NPN&pc=10&ucb=1500&uce=700&ueb=5&ic=2.5&tj=150&ft=7.5&cc=80&hfe=2&caps=TO3

[Cicada]

Look into the NTE catalog for equivalences.

Also in some places (like my country) you can buy NOS over the counter.

I came across the NTE catalogue.  Was not sure how to interpret what they are doing. I searched for BU205 on their website and found this result NTE165. https://www.nteinc.com/search.php
I am not sure if they manufacture their own semiconductors or if they take NOS from other brands and relabel it with their own number. The datasheet values look like it match those of the BU205
https://www.nteinc.com/specs/100to199/pdf/nte165.pdf

I wonder this company compares to Rochester which I think have a very good reputation. They also make devices from original silicon wavers that they have in storage. As far as I know they also manufacture old semi
 waivers under license.

[Benta]

Those transistors are nothing spectacular, typical parts of their era. One is 700/1500 V, the other 300 V. Look out for the switching specs.

The big issue is, that TO-66 parts are unobtainium today, and TO-3 are few and far between.
Good news is, that modern TO-3P (TO-218/TO-247) and TO-220 parts can be used as drop-in replacements, provided you snip off the middle lead.

[strawberry]

KT838A  TO-3 seems most popular USSR TV transistor
some transistors have built in resistors

[Benta]

BU508A. Obsolete, but still available.

[Messtechniker]

Time for a transistor curve tracer.
Pic shows curves for an old (about 1974) BCY 79-9 (Aus UPGR)
and a few new (2021) BCY 79-9 (Reichelt)

[Cicada]

245 equivalents to the bu205 here :

https://alltransistors.com/crsearch.php?mat=Si&struct=NPN&pc=10&ucb=1500&uce=700&ueb=5&ic=2.5&tj=150&ft=7.5&cc=80&hfe=2&caps=TO3

This is exactly what I have been looking for. Enter the transistors parameters and get suggested alternatives. BUT... I think it might have been more relevant in the past since it seems that all alternatives are also not that easily available. Will of course be very handy if you have access to new old stock or if you buy from people that still stock these old devices.

Thanks