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Author
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Topic: MSPF 576 Transistor??
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Dennis Detweiler
Member From: Solon, Iowa, US
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posted 20 May 2005 09:41 AM
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I can't locate this transistor anywhere on the internet or at Radio Shack. It's the only odd transistor on the preamp circuit board in my session 400. Someone replaced it by clipping the leads of the original transistor and soldered the very short leads of a new one (probably a used one) to the old leads (sloppy). Is this transistor still available? Or is there an optional replacement?
Dennis |
Paul Arntson
Member From: Bothell ,WA (just outside Seattle)
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posted 20 May 2005 10:23 AM
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.[This message was edited by Paul Arntson on 24 May 2005 at 08:04 PM.] |
Bob Lawrence
Member From: Lwr Sackville, Nova Scotia, Canada
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posted 20 May 2005 10:54 AM
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Here's the Preamp schematic from Brad Sarno's website. Which transistor is it?Preamp Schematic: http://home.earthlink.net/~bradsarno/session400pre.html Additional 400 info http://home.earthlink.net/~bradsarno/session_400page.html |
Jack Stoner
Sysop From: Inverness, Florida
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posted 20 May 2005 12:48 PM
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I don't recall anything with "MSPF" as a transistor type. MPS or SPS plus a number would be a typical part number. I have a (1997) Peavey cross reference for many tranistors if you can find out what the original one was. |
John Tipka
Member From: Reynoldsburg,OH
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posted 20 May 2005 02:56 PM
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Dennis,
The transistor you are looking for is not an ordinary run-of-the-mill p-n-p or n-p-n bipolar - it's a 2SJ576 - a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET). John |
Dennis Detweiler
Member From: Solon, Iowa, US
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posted 20 May 2005 03:22 PM
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I'm installing a Sarno kit into a 1974 session 400. I have a schematic that is dated 1974. I also have Brad's schematic, which is newer. I notice an extra transistor circuit in the newer schematic. I confirmed this after pulling the chassis out of my 1976 session 400 and visually compared both preamp boards. I got Brad's preamp upgrade finished when I noticed the bad transistor replacement job that was done in the past. I bought the amp new in 1974 and it's had repairs over the years. I'm not sure who did the quickie transistor replacement?
I used a magnifying glass to recheck the numbers on the replaced transistor. It still looks like MSPF. Below the letters it reads, 576. This same transistor is in the 1976 400.
Thanks
Dennis[This message was edited by Dennis Detweiler on 20 May 2005 at 04:22 PM.] |
Jack Stoner
Sysop From: Inverness, Florida
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posted 20 May 2005 05:34 PM
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There is nothing in the Peavey list I have that has "576" in any number.
Also there is no MOSFET listed with that number, either in the Original House Number, Alternate In-House number or Field replacement number. |
Dennis Detweiler
Member From: Solon, Iowa, US
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posted 20 May 2005 05:43 PM
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My schematic literacy isn't very good. But, looking at the schematic, I think it's maybe the tremelo circuit?...it has the numbers 576 next to one of the transistors. ??
Thanks
Dennis |
Paul Arntson
Member From: Bothell ,WA (just outside Seattle)
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posted 20 May 2005 10:47 PM
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.[This message was edited by Paul Arntson on 24 May 2005 at 08:04 PM.] |
Dennis Detweiler
Member From: Solon, Iowa, US
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posted 20 May 2005 11:26 PM
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Thanks for all the replies. Maybe Mike Brown can ask a tech at Peavey and come up with some input.
The transistor hasn't given me any trouble. I don't use the tremolo, so maybe it's not important. I just thought I would put a clean finish to the project if I could replace the transistor with a proper solder joint. I doubt it would break and fall into the circuit board. I'm more concerned that one of the 3 leads would crack at some point. It looks like the leads were just held in place and "blob" soldered together. |
Dennis Detweiler
Member From: Solon, Iowa, US
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posted 21 May 2005 08:28 AM
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I found out that it is a discontinued transistor. So, I'll have to find out from Peavey, if they have a substitute recommendation for replacement.
Thanks for all the input.
DD |
Robert Parent
Member From: Savage, MN
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posted 23 May 2005 04:52 AM
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It sounds to me like one of several Motorola transistors which were speced for PV. I had a LTD with several transistors labeled in a similar way. After much searching I found out direct from Motorola that they were discontinued, a special spec screen for PV, and that info was not available. From my schematic I could tell it was used in the preamp so tried a few general purpose, low noise parts until I found a winner. I also had the same issue with some output power transistors in a different amp. The soultion for those took a bit longer to find some that would work due to the higher voltage if I remember correctly. |
Jack Stoner
Sysop From: Inverness, Florida
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posted 23 May 2005 05:12 AM
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The Peavey transistor list I have, which lists discontinued types and the alternate substitution (and Peavey part number) doesn't list anything even close to this transistor number. But, the comment about custom Motorola transistors is true. I tried to find the transistors that were in the original Boss Tone's and as it turned out the same thing, they were a custom transistor and the information was not available. They were made 35 years ago and they said they don't keep custom specs for components that old, especially since the company is out of business. |
Paul Arntson
Member From: Bothell ,WA (just outside Seattle)
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posted 23 May 2005 08:49 PM
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.[This message was edited by Paul Arntson on 24 May 2005 at 08:04 PM.] |
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