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Replacement Transistors & Substituting

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Replacement Transistors & Substituting

Postby dashpuppy » November 18th, 2019, 1:29 pm

What is your favorite way of finding substitutes & replacement transistors.

I have a list of them I want to find substitutes for, along with converting to SMD..
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Re: Replacement Transistors & Substituting

Postby amb » November 19th, 2019, 1:33 am

There is no hard and fast rule. It depends on what the transistor's function is in the circuit. The basics are that it must be the same basic technology (silicon vs. germanium), polarity (NPN vs. PNP), case style and pin out, voltage, current and power ratings. But in many circumstances the application may be particular about other characteristics such as gain (hfe), high frequency response (ft), noise level, junction capacitances, etc. in order to perform optimally.

Some manufacturers offer cross-reference guides for device substitutions, but they should only be used as a starting point to finding the right parts, based on the aforementioned criteria.

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Re: Replacement Transistors & Substituting

Postby dashpuppy » November 22nd, 2019, 9:07 pm

amb wrote:There is no hard and fast rule. It depends on what the transistor's function is in the circuit. The basics are that it must be the same basic technology (silicon vs. germanium), polarity (NPN vs. PNP), case style and pin out, voltage, current and power ratings. But in many circumstances the application may be particular about other characteristics such as gain (hfe), high frequency response (ft), noise level, junction capacitances, etc. in order to perform optimally.

Some manufacturers offer cross-reference guides for device substitutions, but they should only be used as a starting point to finding the right parts, based on the aforementioned criteria.



Well my Goal is to turn the circuit i have now that uses all Through hole devices into SMD devices, only a hand full of small Transistors to do.
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Re: Replacement Transistors & Substituting

Postby amb » November 22nd, 2019, 10:52 pm

If you post the schematic of the circuit, and describe what it does, then maybe we could offer some suggestions.
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Re: Replacement Transistors & Substituting

Postby dashpuppy » November 25th, 2019, 4:25 pm

amb wrote:If you post the schematic of the circuit, and describe what it does, then maybe we could offer some suggestions.


I asked the Designer of the schematic and he would prefer i don't post the schematic on line! I can give the part numbers or maybe screen shots of certian parts of the schematic.

It's basically an amplifier but wanting to convert front end parts to SMD if possible.
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Re: Replacement Transistors & Substituting

Postby amb » November 25th, 2019, 5:13 pm

The original part numbers would help, but without knowing the operating parameters of the circuit it would be hard to make good suggestions.
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Re: Replacement Transistors & Substituting

Postby dashpuppy » December 2nd, 2019, 2:31 pm

amb wrote:The original part numbers would help, but without knowing the operating parameters of the circuit it would be hard to make good suggestions.



I can use this schematic as it's a bit different. It's the AV800 .

Image
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Re: Replacement Transistors & Substituting

Postby amb » December 3rd, 2019, 4:41 am

- The direct SMD equivalent for the BC546B is BC846B.
- A good SMD substitute for 2SC2240 is FJV1845.
- 2SA1306 and @SC3298 are medium power transistors with high voltage ratings. I can't find good SMD equivalents of these. Perhaps you could bend the leads on these transistors and mount them flat on the board SMD-style, as long as they don't require extra heatsinks.
- The output MOSFETs IRFP240/IRFP9240 are meant to be heatsinked, and there are no SMD equivalents.
- is Q32 a BD681? The schematic is a bit blurred there. If it is, it's also a medium power transistor of high-ish voltage rating. The same comment for 2SC3298 applies here.
- Is Q22 marked IRF9600? Such a device doesn't seem to exist. Maybe it's a IRF9610. At any rate, it's probably a TO-220 package, chosen so that it could be mounted on the main heatsink with the output MOSFETs for thermal feedback. Thus it doesn't make sense to use a SMD device here.
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Re: Replacement Transistors & Substituting

Postby dashpuppy » December 3rd, 2019, 8:40 am

Well my plan is to convert all the "front-end" into smd. I know the irf9610 has to be mounted to the output stage heatsink :) I also know that the outputs have to be mounted to heatsink :P

Goal output stage as one pcb doubble layer with 2oz copper small size SMD resistors.
Goal Front-end small pcb 2oz copper and all smd if possible.

The amplifier is capable of 800watts into 4 ohm with 95v rails but there is now way in HELL ill need that much power maybe 120 MAX peak, BUT the project is for fun and to build it into SMD and learn & have fun ! I know it's possible just have to dig & experiment! I also just bought 4 x av800 pcb's :) so in therory i could build the through hole version then tack on the smd part's to the pcb's and do testing on the bench.



amb wrote:- The direct SMD equivalent for the BC546B is BC846B.
- A good SMD substitute for 2SC2240 is FJV1845.
- 2SA1306 and @SC3298 are medium power transistors with high voltage ratings. I can't find good SMD equivalents of these. Perhaps you could bend the leads on these transistors and mount them flat on the board SMD-style, as long as they don't require extra heatsinks.
- The output MOSFETs IRFP240/IRFP9240 are meant to be heatsinked, and there are no SMD equivalents.
- is Q32 a BD681? The schematic is a bit blurred there. If it is, it's also a medium power transistor of high-ish voltage rating. The same comment for 2SC3298 applies here.
- Is Q22 marked IRF9600? Such a device doesn't seem to exist. Maybe it's a IRF9610. At any rate, it's probably a TO-220 package, chosen so that it could be mounted on the main heatsink with the output MOSFETs for thermal feedback. Thus it doesn't make sense to use a SMD device here.
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