Iam looking for a good replacement for 1854-433

[hnjmkl]

Hi, I ask with which transistor to replace the 1854-433 placed on the +17 V. positive branch of my 8012B being repaired. the manual only specifies 80W 2MHz device.

[Hamelec]

it is a NPN in the power supply, not a very special transistor.
Depending on the package take something like a 2N3055 / BD245 ..

[Edwin G. Pettis]

Hello, the 1854-0433 was sourced from Motorola at the time (ON-Semi) and the commercial version of it was SJE931.  I don't have a full data sheet on it but Vce=60V, Ia= 10A, 90 watts shouldn't be too hard to find a replacement.  I don't know if any SJE931 is available, they date back to the 70s.

[hnjmkl]

thank you for the very useful information, certainly it is not easy to find a TR with those characteristics in TO126.

[Kleinstein]

A TO 126 is a bit small for that level of power. So there is likely something wrong. Chances are a modern part would be more like TO220 or even larger.

If available the circuit diagram around where the transistor is used can help. When looking for a replacement part it is a good idea to look at the plan anyway as the relevant parameters can vary with the circuit. 

[floobydust]

thank you for the very useful information, certainly it is not easy to find a TR with those characteristics in TO126.

Is it TO-126 package? I think it must be TO-220. Q43 pass transistor with uA723 for +17V rail, on A6 board.

[Hamelec]

i think the power supply is designed for 0.5-1A only (according the 1000µF cap in) and almost every NPN transistor >20W and >30V can do the job..

[hnjmkl]

The package is TO126, the latest information is certainly helpful in choosing the replacement, thank you, Franco

[Kleinstein]

The transistor for a power supply is not that critical. In a good design the voltage drop should not be very high to run into SOA problems. So the main point would be to find an NPN that can handle relatively much power in the given small case at you favorite ssupplier.   E.g. a BD437 or BD177 could be an OK choice.

The heat sink size could also give clue about the heat level expected.

If the heat sink is large and there is space one could consider a slightly larger TO220 or similar case.

[Hamelec]

..but be aware:
TO126 and TO220 having different pinout (ECB vs BCE)

[Edwin G. Pettis]

Frankly that 10A rating is suspect for a TO-126 package, but if the power supply is limited to under 2A I would look for either a BD189 or 2N5191/2N5192 transistors, they should be able to take the current and have a Vceo of 60V, the BD437 is only rated to 45V Vceo so it may not work.

[hnjmkl]

Hi At a low price in France on ebay I bought N. 4 2N5192A, from the suggestions I received I think they are largely adequate as substitutes, once the +17 has been fixed I will have much greater problems with the circuit than this 8012B. Bought dead for $40.

[hnjmkl]

I got the 2N5192G, unfortunately the package is a small version compared to the 1854-433, I have trouble understanding what the pacage of this transistor is called.

[Hamelec]

I have trouble understanding why you would fix a 8012 without any idea of hardware.

[hnjmkl]

I ordered some TIP3055. C-E are reversed but patience.

[Clear as mud]

This may be helpful: Common Transistor Cases

I also just found this: HP / Agilent Service and Repair Parts and Cross Reference Information.  If you scroll part of the way down the page, there is a link to a .pdf file with HP part numbers cross-referenced to industry standard part numbers.

[hnjmkl]

Thank you last suggestion for tracing the case of 1854-433, I have concluded that the case is not standard, as it does not match any current model, in any case I have ordered some TIP3055's and will try to fit it on the board.

[hnjmkl]

Well, the TIP3055 successfully replaced the failing transistor, now the +17 is restored.
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