Interesting idea. I always wanted to build an "SS Champ" . Not efficient but the original tubed one is even worse!!!! I think that an IRFP250, which I use a lot in my 300W up amplifiers, will work nicely here . Of course I´ll have to design and build the O.T. What others describe (rightly) as "bass problems" , I think really means "very saturated core"; it definitely will need a gap.

As far as I know, SLM was sold a couple of years ago to LOUD Technologies , including Crate and Ampeg trademarks. They closed their almost 200 employee plant in USA (keeping only some administrative and technical personnel) and set up factory in Viet Nam, currently cheaper than China. *Maybe* they perceive Crate as a "lesser" brand, which I regret. Their products are good, innovative, and , under the skin, the same as modern so called "Ampegs". If somebody has fresher news than mine , please post them.

Mansur, just this: EX-CEL-LENT !!!! Congratulations. Please tell us something about the power amp, speakers,your guitar,  and how the demo was recorded, everything has influence on the final sound. Congratulations again.

Dear Rob: a "Plan B" solution that I´ve sometimes used with those beasts, after I got tired of replacing blown parts,and learning that the switching power transformer was absolutely unavailable, was to simply ditch the switching board and convert it to a "regular" power supply (which is the *other* version of the same amp). The 50/60 Hz power transformer is slightly too thick to fit fully into the original chassis, so I cut a "window" in the aluminum bottom panel , let less than 1 cm of (properly insulated) windings show through it and used 4 oversize rubber feet yo avoid it touching the speaker box. In a MB150 combo, that wasn´t even necessary. That "solution", by the way, is used by GK themselves . Cheers.

Looks great. Definitely it will *drive* your tank, and then some. Congratulations.

Check that the new pot was correctly soldered (sometimes the solder goes *around* the pot pin without being actually soldered to it),  check that some solder blob isn't shorting something it shouldn't, and last but not least, sometimes a PCB track (specially the thin/skinny ones) get cracked about 1mm from the actual soldered pad: in that case scratch carefully the (usually green or blue) solder mask and solder a tiny piece of wire to repair it. Good luck.

Sometimes I can't but wonder what the heck were the guys at runoffgroove.com thinking. (2)
Dear Teemuk, I couldn't agree more with you.
ROG's ideas are the worst "design" technique I've ever seen, and I've seen quite a few (just as you). Original (tube) circuits component values are NOT "pulled out of the blue" , but carefully calculated to get a given optimal "working point", gain, bias, signal handling and, where appropriate, distortion. None of that is considered by ROG, who probably thinks that "original" resistor values are somewhat magical and shouldn't be messed with. But they mess with everything else!!! Just as an example: a 12AX7 with 820 ohms in its cathode and 100K on its anode has a gain around 50/60, can output around 60 clean RMS volts and stands around 1,5 Vac in its grid (and will stand without dying around 100Vac there, if so supplied by a previous tube). An MPF102 or similar will be grossly underbiased by an 820 ohm resistor (it would need from 2k2 to 10k) and the gain is a meager 3 to 6. Just Proto one and see!! To make matters worse,the so called "100k bias trimmer" is a "max"value 100 k Load Resistor and never used in that value, but typically from 1k5 to 10k at best. The rest of their assumptions are similarly way off the mark. Do they sound good? Well, some do, being minimalistic Fet preamps, sometimes (easily) overdriven. Do they sound like a Princeton/Plexi/Matchless/Hiwatt, etc.? Definitely not!!!! Can Fets be used to get a good guitar sound!! Yes, emphatically, but using datasheets ,measuring them, and using normal good design techniques.

Hi Jeansen. Whay your repairman did, what I call "touch up" is just getting a small/fine tip soldering iron (30/40W), very clean tip, and some thin, good quality solder wire (preferably around 0,7mm) and very briefly re-solder suspect solder joints, adding the tiniest amount of solder possible (just for the rosin core/flux, rather than  the metal itself). The idea is to get any "cold" or cracked solder joint "re-joined" , NOT to make a blob , a messy joint or even worse a short to some nearby track or pad nor melt any plastic nearby. What is your original language?
JM

Thanks Teemuk. Always felt curious about "steel amps" , whether they were "special" or just regular guitar amps. JM

Dear Brooklynhero. I think that first of all, you should try to get the schematic. I´ve got it somewhere, but to save time, try to get it yourself. The Carvin guys are great and helpful, you can download it from their site, I think that section is called something like "legacy", "museum", or something like that. Not very sure now, but it either used a lot of MOS devices or "heavy" bipolars such as MJL21194 or similar. Anyway, I remember it was a big, professional head. I´ll check it when I get to my workshop. I think that that 5W resistor (value?) is not "across" your "power input" but very probably is an output transistor emitter resistor, indicating very probably a shorted output device. See you soon.
JM.

You can squirt a *very* small amount of contact cleaner into the input jack, and them move a plug in/out 10/20 times. This will physically clean the rust/mold/dirt that disturbs good contact. Afterwards, you can "touch up"the solder joints to make sure there are no cracks, which are very probable since this is thesingle most abused jack in the amp. Basically: the same that Teemuk and Jack suggested, applied to this jack.
Good luck.
JM.

Hi Dori.
I guess that the *best* mod you'll begin with, is to get a decent 12" guitar speaker, build a very simple box for it, and use your Squire only as a head, running your speaker wires straight to the better, improved, external one, unhooking the cheesy internal one.
You'll have better treble, lots of extra bass, and the distortion will improve a lot.
If you have the schematic, please share it with us.
Bye
JM

Hi Rowdy. Teemuk has already been so kind as to post a link for free Spice (I think he uses that version, if I remember correctly) it is: http://www.linear.com/designtools/software/#Spice  I haven´t used it myself, but if the Master says it works ... I wouldn´t doubt it.
As Jack says: "Rock on"
Keep posting your experiments.
JM.

Dear Rowdy.
Nice try, specially as a first design, but I think that in this case you´ll get far better results going bipolar.
The reason is you only have 12 Volts, and MosFets, being enhancement devices, "lose" around 4 volts each, just getting forward biased , and a couple more volts getting really turned on. (Look at their Current vs. gate voltage graphs) . With two of them in series, you have *very* little useful voltage left.
Besides, the "class A" design uses a lot of DC current, just heating the devices. A TDA2002/2003/2006/LM383 or similar would give you around 6 clean Watts into 4 ohms and be a far simpler circuit , with the same 12 Volts. (check their datasheets)
Congratulations.
JM

Dear ADV: trying to open "WWW.loudtechnologies.com/25001h4_.pdf" gets me nowhere.
Googling "25001h4_.pdf " neither.
Would you be so kind as to post the full working link here?
Thanks a lot.
JM