Adcom gfp-1A preamp from the early 90s with dead power supply: transistor regulator on +ve rail is blown; its a motorola MDS 9401, to-202 case with e-b-c pin out. Google didn't turn up any other specs on this transistor, nor a supplier for this now obsolete transistor. Anyone have a datasheet or know where to get these? Willing to use a suitable substitution, but don't know what are needed specs and pin out doesn't match more common to-220 or to-126 transistors.
Thanks in advance for anyone who can offer any help...
Thanks in advance for anyone who can offer any help...
Is your collector terminal + voltage or minus vs emitter terminal? + is probably NPN, - is probably PNP. The details of how the base is driven will determine for sure. Make sure replacement transistor Vceo is higher than rail voltage (if <1 ma Vceo rating) or 50% higher (if >10 ma Vceo). > 10 ma Vceo ratings are a big lie, nobody buys a transistor to leak that much off, but everybody rates it that way now. You can probably buy a TO202 transistor like NTE49 (npn) or NTE50 (pnp) but you'll pay a shipping charge from a big warehouse. Probably easier to buy a TO220 and twist the leads around. TIP41C (npn) and TIP42C (pnp) are what I keep around to do middle sized jobs, they have a Vceo of 100. How old and leaky is the filter cap? Transistors go for a reason.
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Thanks for the input, indianajo.
The MDS 9401 is an NPN. According to the NTE site, it actually crosses to an NTE184...BUT that's a TO-126 with a pin arrangement of ECB and the MDS9401 is a TO-202 with a EBC pin arrangement! The NTE49 is a better match (at least its a TO-202) but is no longer available from NTE. Don't really want to, or can, twist the leads on a TO220 since the space on the board is limited. You're right about the caps, the plan is tor replace all the electrolytics in the PS once I get hold of the transistor.
The MDS 9401 is an NPN. According to the NTE site, it actually crosses to an NTE184...BUT that's a TO-126 with a pin arrangement of ECB and the MDS9401 is a TO-202 with a EBC pin arrangement! The NTE49 is a better match (at least its a TO-202) but is no longer available from NTE. Don't really want to, or can, twist the leads on a TO220 since the space on the board is limited. You're right about the caps, the plan is tor replace all the electrolytics in the PS once I get hold of the transistor.
Newark doesn't have TO202 or TO5 either except darlington. Pick up an old TV off the curb, they are full of TO5 stuff. TO5 is EBC. I've got boards of old junk around here like that. I'm looking at a Wyse terminal board I pulled from the trash can about 1986 with 2 or 3 TO5 transistors on it. I've already salvaged out the resistors diodes and disk caps. Used the diodes already, I blew about 20 diodes when I plugged an amp driver board in to the output assy 1 pin off. Takes 3-4 days and $10 freight to get anything around here, RS has batteries and cell phones and toy cars- only.
I checked Mouser, and they don't carry any TO-202. Some more web searches showed that Central Semiconductor still makes 2N6553, here's link to the datasheet: 2N6553 datasheet pdf datenblatt - Central Semiconductor Corp - Power Transistors ::: ALLDATASHEET :::
I estimate that the rail voltage is about 30V (based on the fact that the caps downstream from the transistor are rated at 35V) so with a Vceo of 100V the 2N6553 seems to fit the bill. Is there any other specs. I should worry about for this application?
I estimate that the rail voltage is about 30V (based on the fact that the caps downstream from the transistor are rated at 35V) so with a Vceo of 100V the 2N6553 seems to fit the bill. Is there any other specs. I should worry about for this application?
I hate alldatasheet.com, they have a tiny picture of page 1 but you can't read it. Try datasheetcatalog.com, their datasheets you can actually read.
Some transistors are higher gain than others, hope your circuit is not sensitive to that as you don't have much choice. Some transistors are lower noise than others, or more suited to amplifiers than switches. Amplifier application is in the text on the datasheet. Lots of people are using switcher 2n2222 on their AO39 reverb on Hammond organs, instead of the Ge original transistor so using a switch for an amp is not tragic, just not ideal. 35 V is lower Vceo voltage than about anything developed after 1970. 2N2219 was the most common TO5 transistor, which was EBC, but the only metal can newark had was TO18. Pinout is fine on TO18 but the power dissipation may be wimpy on a TO18 for a TO202 application. If you do buy a TO5 transistor, try to get a TO5 heat sink at the same time. Again, junk will have the heat sinks in there. The bad thing about junk, you might get real high voltage transistors that are not suited for audio medium current. Look at the capacitor ratings hooked up to any transistors from junk to figure out what the transistor is used for. Suffix K,L, M on the ceramic caps, your into the HV parts of the TV, no good for audio. The numbers on junk transistors are useless, everybody had house numbers that meant nothing.
There are a couple of distributors in Vancouver, tickle them and see what they have.
I buy some things from electronicsurplus.com in Buffalo NY, their service is okay but their prices are high on obsolete semiconductors. They do have them, though. Apexelectronic.com in LA is also a surplus house. Both have a minimum order, buy some teflon or kynar insulated non-ROHS wire or something. I'm having a ball with the kynar, you can't burn it with a soldering iron unless you try hard. I got some nice 8 gang fuse holders I saw into singles and doubles, and some nice pushbutton switches from e-surplus last time I bought. Both electronicsurplus and apexelectronic charge minimum $10 freight (USPS priority boxes) and higher for export probably.
Somebody on the bargain board below on this website might have something.
Some transistors are higher gain than others, hope your circuit is not sensitive to that as you don't have much choice. Some transistors are lower noise than others, or more suited to amplifiers than switches. Amplifier application is in the text on the datasheet. Lots of people are using switcher 2n2222 on their AO39 reverb on Hammond organs, instead of the Ge original transistor so using a switch for an amp is not tragic, just not ideal. 35 V is lower Vceo voltage than about anything developed after 1970. 2N2219 was the most common TO5 transistor, which was EBC, but the only metal can newark had was TO18. Pinout is fine on TO18 but the power dissipation may be wimpy on a TO18 for a TO202 application. If you do buy a TO5 transistor, try to get a TO5 heat sink at the same time. Again, junk will have the heat sinks in there. The bad thing about junk, you might get real high voltage transistors that are not suited for audio medium current. Look at the capacitor ratings hooked up to any transistors from junk to figure out what the transistor is used for. Suffix K,L, M on the ceramic caps, your into the HV parts of the TV, no good for audio. The numbers on junk transistors are useless, everybody had house numbers that meant nothing.
There are a couple of distributors in Vancouver, tickle them and see what they have.
I buy some things from electronicsurplus.com in Buffalo NY, their service is okay but their prices are high on obsolete semiconductors. They do have them, though. Apexelectronic.com in LA is also a surplus house. Both have a minimum order, buy some teflon or kynar insulated non-ROHS wire or something. I'm having a ball with the kynar, you can't burn it with a soldering iron unless you try hard. I got some nice 8 gang fuse holders I saw into singles and doubles, and some nice pushbutton switches from e-surplus last time I bought. Both electronicsurplus and apexelectronic charge minimum $10 freight (USPS priority boxes) and higher for export probably.
Somebody on the bargain board below on this website might have something.
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