Hi all, I was given an Earth Original 2000 guitar/bass head with matching 1x15 cab a few years ago, and used it as a practice bass amp. One night while the amp was on, sitting idle, it developed a light buzz, then popped the fuse a few seconds later. I replaced the fuse and it blew almost immediately. I checked the rectifiers in the power supply (no problems there), and power transistors, found 2 of the 4 output transistors are shot. I set it aside awaiting some spare time. It's been sitting for 2 years. Now I finally have the time to tear into it, and pulled the transistors to order replacements...
and that is where the problem starts. I can't find any info on these transistors searching the internet by part number, can't find a match in any of my NTE or SK manuals. I was able to find a possible manufacturer by the "S" logo on the transistor (Not Sanyo), which appears to be Semtech. I sent them an email with the part number, they have no idea what it is. SO now, I'm looking into just finding out what commonly available transistors I can install. I plan on replacing all 4. I don't have much experience with solid-state power amps outside of replacing transistors and fixing power supplies. Tube amps are my forte and I haven't really taken the time to delve too deep into solid-state design, and hopefully I won't have to for this amp. I know something made the transistors blow, and know I'll have to check everything else in the amp, but would like to start here.
THe amp is an Earth Sound Research Original 2000, 130w, with 340 power module (made by ISC Audio). I know most Earth solid-state amp designs were Peavey rip-offs, and am assuming there is an almost identical 130w solid-state Peavey power amp module that I can get a schematic for and make life easier. I'm also assuming the transistors are NPN, around 30w each.
Years ago I rebuilt an Earth B-2000 Super Bass tube amp, added 7-band tube EQ (lifted that design from a Blonder-Tongue hifi tube EQ), added effects loop, bar graph-type eye tube indicators and it has been my main amp for years. I no longer play due to arthritis and have sold off most of my equipment and all but a couple basses. I plan to keep the Earth tube head (only because I put so much time and money into it) and this Original 2000. It's a nice plug-n-play amp, the exact opposite of what I turned my Earth Super Bass head into.
The original transistor markings are as follows:
S (logo)
59-4004-C
7624
ANy info on the transistors, or similar drop-in replacement would be a big help. Also any service literature on this amp, or if anybody knows what the Peavey relative of this amp would be would help a great deal. Thanks!
and that is where the problem starts. I can't find any info on these transistors searching the internet by part number, can't find a match in any of my NTE or SK manuals. I was able to find a possible manufacturer by the "S" logo on the transistor (Not Sanyo), which appears to be Semtech. I sent them an email with the part number, they have no idea what it is. SO now, I'm looking into just finding out what commonly available transistors I can install. I plan on replacing all 4. I don't have much experience with solid-state power amps outside of replacing transistors and fixing power supplies. Tube amps are my forte and I haven't really taken the time to delve too deep into solid-state design, and hopefully I won't have to for this amp. I know something made the transistors blow, and know I'll have to check everything else in the amp, but would like to start here.
THe amp is an Earth Sound Research Original 2000, 130w, with 340 power module (made by ISC Audio). I know most Earth solid-state amp designs were Peavey rip-offs, and am assuming there is an almost identical 130w solid-state Peavey power amp module that I can get a schematic for and make life easier. I'm also assuming the transistors are NPN, around 30w each.
Years ago I rebuilt an Earth B-2000 Super Bass tube amp, added 7-band tube EQ (lifted that design from a Blonder-Tongue hifi tube EQ), added effects loop, bar graph-type eye tube indicators and it has been my main amp for years. I no longer play due to arthritis and have sold off most of my equipment and all but a couple basses. I plan to keep the Earth tube head (only because I put so much time and money into it) and this Original 2000. It's a nice plug-n-play amp, the exact opposite of what I turned my Earth Super Bass head into.
The original transistor markings are as follows:
S (logo)
59-4004-C
7624
ANy info on the transistors, or similar drop-in replacement would be a big help. Also any service literature on this amp, or if anybody knows what the Peavey relative of this amp would be would help a great deal. Thanks!
The "S" is probably Solitron considering the year of manufacture, 1976. I'm assuming they are TO-3 style. As you already know they are pretty much Peavey amps or damn close to it, I would just throw in some new ON Semi MJ21193/4s.
Craig
Craig
I would be careful putting in newer transistors.
I did that with a 1980's Maplin amp and it oscillated badly.
I had to adjust the VAS capacitor to stop the oscillation.
I checked the new transistors on a component analyser and they had much higher gain than the original.
I did that with a 1980's Maplin amp and it oscillated badly.
I had to adjust the VAS capacitor to stop the oscillation.
I checked the new transistors on a component analyser and they had much higher gain than the original.
It is very likely a straight lift of a Peavey circuit, Peavey sued them out of existence for exactly that. Especially if you find all four are NPN, PV designs were almost all quasicomplementary in that era.
That number is probably just a house number. And 7624 is the date code. All the PV amps of the era used essentially MJ15003, which is what I would recommend.
That number is probably just a house number. And 7624 is the date code. All the PV amps of the era used essentially MJ15003, which is what I would recommend.
THanks for the help, I'll get a few MJ15003s on order, data sheet info looks like they would be run fairly conservatively here. I've also got a PEavey Super FEstival 400 I've had for years, I got it in trade with a Peavey 412F cab for an Epiphone EB-3 bass. Got home plugged it in, turned it on, and watched smoke start seeping from 4 very specific spots in the cab's grille cloth. THat amp is next after I get this Original 2000 going again. I don't need the Super Festival head, but would like to use it at least once before I sell it, considering I traded one of my favorite basses for it and has been sitting since 2004. BEfore I ended up with this Earth Original 2k, it sat in the front room of the computer repair shop where I was working at the time, atop the 1x15 cab. One day a customer came in and stood staring at the amp and cab for a couple minutes. I asked him if he wanted to buy it, he said no, and that he'd worked for PEavey around the time they sued Earth Sound Research, and had a bit of a flashback when he saw the logo. I live in northwest FLorida so running into people associated with Peavey, Peavey dealers, repair techs, etc, isn't uncommon (unless I need help with one). He told me the whole story behind Earth and Peavey, quite an ordeal it sounds like. I heard a while back that most of their tube heads were Fender knockoffs, but the old 4x 6L6 100w design has been around so long and used by so many companies I think that is a kind of unfair accusation. But with the Original 2000, even the lettering on the back of the amp looks like every solid-state Peavey I've used or lugged around. THe 1x15 cab even has the brushed aluminum strips down the sides of the grille like Peavey used. Kind of hard to hide their intentions there.
Oh, I did connect the 2 surviving transistors to an Atlas DCA, which shows that they're NPN. SAme part numbers as the dead ones.
You might be lucky and just have a couple dead outputs, but ALWAYS check the resistors associated with them, they can burn open. Plus always good to check the drivers that drive the outputs.
As well as the bias stack. "Developing a buzz" is often an indication of high current draw (high ripple on the supply, maybe even tens of volts). If the bias somehow drifted to a high value due to an open pot, resistor or diode it can take outputs with it a few seconds/minutes later. We had a Flame Linear bias itself into class A due to base-emitter short in the predriver. Ran hot as hell but still worked. Lasted about an hour into a show before it finally failed completely.
I'll be ordering a set of transistors for the Earth Original tomorrow. Before I order, does anybody have any suggestions on what the Peavey Super Festival Series (uses 800 Module) 400w (front nameplate missing, it's a 400w amp, but not certain of the exact model) would use? I'd like to get some for it on the same order to save a bit on shipping, but don't have room on my bench to drag it out and tear into it at the moment. I'm sure it'll need a new set, used 8 or 10 output transistors if I remember correctly.
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