Are you familiar with Elliot Sound Products?  He has a lm3886 project...even a pcb.

http://sound.westhost.com/project19.htm

I like the 'suit case' design here.  It has given me ideas for an old coronet case I have.   :dbtu:

When you say supply caps, do you mean c46 and c47?  The ones next to the zeners?

Wow.  This forum has attracted some cranky customers lately.

This is how guitar amps with minor problems end up selling for pennies on the dollar on craigslist - maladjusted operator headspace.  :loco

It's not a scientific survey, but I have worked on a number of the little fender r15s, and I would say broken jacks are way more common failure than output device.  I think little amps on the floor get kicked around a lot easier, also dropped.  If you trip on a JC120, you might hurt your toe but if you kick over a little frontman, the guitar plug can act like a lever and break the jack or even crack the PCB.  Also, for what they are, I think those frontmans sound pretty decent, especially if you put it into larger speakers than the 8" it comes with.  The preamp might be more complicated than you are looking for since it has a tone stack and distortion stage, but its basically two chips some pots and various R and C.


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I know the original poster wants to make his own and I appreciate the challenge in that, but if I might suggest finding an original and just keeping it in playing order might be best .  In kind of kicking myself for not ordering 100 extra 2n5484 back when mouser had them.


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thermistor..

Added: The thermistor is mounted to the chassis with a bolt with star washer and the leads go to a tag strip and then wires back to the board.

Also, as loudthud mentioned above about the rectifier, it is not shown here but is also mounted to the chassis as he suggested.

The chassis is at least 1/8" thick.  There is nothing flimsy on these amps.  The circuit board is thick, too.

Here is another of the board...

Okay, so here is what mine looks like.  YMMV.  The thermistor is on the chassis, between the four outputs.  The 914 diodes are by the connectors and the tip31c in shot #2, the 1n4003 diodes are near the emitter resistors and between the connectors.  the thermistor is red and white and has a marking 750A703-2.

I realize I won't win any awards for photography, so let me know if you have questions about what you see.

Hope that helps.

I have a 1983 Randall rg80/100 es.   I can take some shots tonight if that helps.  The heat sink is as JMF described, the whole chassis itself.  It's very thick aluminum.


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I'd say get it working correctly and leave it cosmetically in its current funky glory. 


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Do a search on "preamp from hell". I think a board layout was done.   I am fussing with a nine volt SMP version but its not ready .


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My beloved Randall uses TIS -58 or also 2N5484.  The latter used to be available at mouser, but lately is listed as obsolete.  Also pinout is different:  tis-58 is D-G-S, 2n5484 is G-S-D.  I have bent the pins to make it work in a pinch.

if you were designing from scratch I guess you could use sot-23 MMBF5484, potentially you could use mmbf5484 in a breakout board and retro-fit to your circuit but that seems like way too much work.

According to orange web site they only supply schematics to "authorised   repair centres" or dealers.

Assuming you didn't mean that you took the amp with you to the bathroom, how did you leave it (running?) and fir how long?  Did it get knocked over or anything like that? Did it have phones plugged in ir guitar plugged in?


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