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8116A Code 42

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Mick B:
Yep, TO18 that's the same conclusion I came to. Compare this datasheet 2N5771 to the 2N4209. also, I have the heatsink on it.
can you believe they want $17. plus, about $8. freight for that 28c part. NO lube and you don't even get a kiss.

Working on the 3 coax cables for the HP 5005A. Trying to reuse their old ferrule and hold-down/strain relief that were bent in the removal process is turning out to be quite challenging. I did find a sheath to use from an 02 sensor I changed out last weekend.
Slow going, but going

MarkL:

--- Quote from: Mick B on August 02, 2024, 06:17:02 pm ---Yep, TO18 that's the same conclusion I came to. Compare this datasheet 2N5771 to the 2N4209. also, I have the heatsink on it.
can you believe they want $17. plus, about $8. freight for that 28c part. NO lube and you don't even get a kiss.
...

--- End quote ---
Hmmm...  I don't see any differences with the electrical specs on the 2N5771 either, apart from the case as you point out.  However (and even though the thermal resistance characteristics are essentially the same), the 2N4209 has a much higher power dissipation of 1.2W vs. 350mW.

You could measure the quiescent Vbe and the voltage across collector resistor R526 to calculate if you're near or above 350mW.  Unfortunately, if R526 is close to 12.1V, then the parallel VR502 will interfere with the measurement, in which case you could more annoyingly measure across all the emitter resistors R519, R521, R523, R529, and R531 to compute the total collector current.

Mick B:


--- Quote --- Quote from: MarkL on: Today at 04:14:00 pm
You could measure the quiescent Vbe and the voltage across collector resistor R526 to calculate if you're near or above 350mW.  Unfortunately, if R526 is close to 12.1V, then the parallel VR502 will interfere with the measurement, in which case you could more annoyingly measure across all the emitter resistors R519, R521, R523, R529, and R531 to compute the total collector current.

--- End quote ---

Well, fortunately all those resistors are exposed I could do that. but to what end? The 2N4209 is not available until Jan (maybe) I waited over a year for an opamp to fix a power supply once. Here are the specs on the heatsink, It's better than a poke in the eye with a sharp stick. I Unfortunately am an expert at this comparison.

I have some Sunon 12V fans I could mount it up front where it would blow directly on Q502 and Q501. OVERKILL? 
I will post the heatsink & fan specs
 

MarkL:

--- Quote from: Mick B on August 02, 2024, 10:53:34 pm ---

--- Quote --- Quote from: MarkL on: Today at 04:14:00 pm
You could measure the quiescent Vbe and the voltage across collector resistor R526 to calculate if you're near or above 350mW.  Unfortunately, if R526 is close to 12.1V, then the parallel VR502 will interfere with the measurement, in which case you could more annoyingly measure across all the emitter resistors R519, R521, R523, R529, and R531 to compute the total collector current.

--- End quote ---

Well, fortunately all those resistors are exposed I could do that. but to what end? The 2N4209 is not available until Jan (maybe) I waited over a year for an opamp to fix a power supply once. Here are the specs on the heatsink, It's better than a poke in the eye with a sharp stick. I Unfortunately am an expert at this comparison.

I have some Sunon 12V fans I could mount it up front where it would blow directly on Q502 and Q501. OVERKILL? 
I will post the heatsink & fan specs

--- End quote ---
To what end?  To determine if your substitute is above the max power spec.  We already know a lot of components in this circuit run hot and HP may have designed Q502 to normally run above 350mW.

It's odd that the lower power dissipation of the 2N5771 is not reflected in any other parameter compared to the 2N4209, but I'm not a semiconductor designer.  Maybe there's something in the structure of the die that it can't support more power, or something else I'm overlooking.  But in general, when I select a part I make sure I stay within the specs and not think I know more than the manufacturer.

Fan or heatsink, if you're above 350mW, you're out of spec.  It's your unit - check the power dissipation of Q502 or not.

Mick B:
Mark, the point of "to what end that would be me thinking out loud
If it's out of spec there is nothing, I can do about it, well maybe a fan, at least until Jan. and then it wouldn't matter. and do I want to spend another $25.00 on it? I'm into it for a bunch already. OF CORSE I DO! I have to remind myself occasionally why". 

 The whole purpose of this is a learning experience, I have a working one with OPT. 001. (we fixed) This has been a wonderful learning experience, with your guidance, I will definitely check the power dissipation of Q502, I had no idea how to do this before yesterday. I just put in this part knowing that the TO92 pkg. was only 350mW this was the closest thing I could find, hence the heatsink, I was waiting for it to go up in smoke, but it didn't. now I am questioning if this is overheating and not going up in smoke but causing distortion resulting in overshoot & high slew rate. 
Be easy on me, I'm in my 70's and just started getting into electronics on a component level a short while ago to occupy myself after physical injuries retired me. I'm a fast learner. most times.
I will post the results for Q502 after repairing the HP5005A, perhaps tommorow. Once again Mark, thanks for your help. I'm just sorry you don't live next door.   

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