Thamks A LOT for a great article and an intensive investigation.

Dear Piter, Marek and Teemu: thanks for the incredible study on cabinet simulators. I see a lot of work was done there. It´s a very important part of SS amps design, trying to get them away from the "cold, sterile" label given them by tubeheads. Cabsims show the way to go. Thanks.

Dear Armstrom. I bolt my 100W poweramps (Tip141/142) to a 2mm aluminum backpanel and one heatsink, basically the same as yours, on its outer side. No thermal problems, at least on the last 15 or 20 years.  For a 70W chip such as yours, using your sink "alone", without any extra aluminum "help", probably will be be enough, if placed in a ventilated place (not inside a basically closed enclosure). Anyway joining 2 (or 3) sinks is not a bad idea at all, there´s not such a thing as "overheatsinking"

Dear CASIOMAX . The output from a PC is often enough to drive fully a poweramp. A problem arises from the "strange" grounding used by their switching offline power supplies. I have seen many perfectly working PCs that light a neon screwdriver that touches their cases (their "audio ground"), besides , the audio signal is sometimes "dirty", meaning it carries "digital interference or junk" mixed in. It shouldn´t but .... often it does. I have repaired a few guitar amplifiers that blew after such a hookup. I don´t know if they became unstable and oscillated, received high frequency switching junk or the "spark" caused by the voltage difference between their grounds burst one of the power amp input transistors, buy anyway they were very dead.

This is a shot in the dark, but without extra information I would guess that they should be wired in parallel (4 ohms). They *might* have been wired in series to allow using an extension box (perhaps 4 ohms) and yet not go very much below the acceptable impedance. Try it watching for signs of overheating.

Not quite "solid state", but we´ll try to help our "old technology" friend.   If that preset pot reads 10K and is connected by track or wire to the  diode that lives on the upper right part of your picture ... yes. Try to get around -39 Volts on the negative side of the electrolytic that lives on its right, which should read 47 uF. Having a generator and scope would be better, but those -39 are a pretty standard value for EL34´s. Don´t touch anything else, be *very* careful with the 400+ volts you´ll find everywhere inside that chassis, specially since I don´t see the 150K 1W equalizing/discharging resistors that should exist in parallel with every big blue 68 uF high voltage capacitor. Please post your results here.

Hi David Shuier, if I decode you correctly. I´m guessing you mean you have basically "no sound" from 0 to 9, but normal sound (no distortion, no farting) from 9 to 10? Is that so?. In that case, probably you have an internally cracked pot. To check that with minimum dissassembly, put it on 5, and solder in parallel with it (pin-for-pin) a new, known good pot, of the same value, with 3 short pieces of wire. If the "external pot" works properly, use it to replace the bad one. Good luck.

Dear Dellamorte: to begin with, congratulations for your great work. 2) I don´t think you´ll be able to fit everyting into the small board Free Eagle allows you, and that without the pots or switches, what will turn your preamp into a messy wire jungle. Please consider copying the original preamp layout which can be easily found on the net (if you can´t, I can send you a copy) Just print it 1:1 size (2 or 3 sheets of paper) and copy it by hand using first pencil and then China Ink, on tracing paper. I think it will be the fastest and less frustrating option. And, BTW, build the full preamp, even if you won´t be using some of its features. Good luck with the project.

Heatsinks are great, but they have one problem: beyond a certain power level they use too much space, and, as Teemuk pointed, the fins have to be vertical for proper convection cooling, which also limits the size. Most of them are aluminum extrusions, and, obviously, the fins must be along the extrusion axis. You can get them as long as you want (I can buy them in up to 6 meter lengths directly from the factory) but the widh is limited to around 16 cm maximum. I have seen US made heatsinks up to 25 cm wide, they were VERY expensive. The hydraulic press and dies used must be monstrous.  For me, the breaking ($$$$) point is 100/200 Watts RMS. For 50/60 W amps: just the 2mm aluminum backpanel; for 100W: 2 mm backpanel and ventilation slots in the cabinet or 115Hx50V mm heatsink with 20 18 mm vertical fins (small and very efficient), this one is *externally* attached to the aluminum backpanel . For 200W: two heatsinks as before. For 300W: a larger backpanel (500x200 mm), with 2 folded ribs reducing the apparent height to 160 mm AND a PC power supply fan (quite silent). It works far cooler (read: safer) than any of the passively cooled ones AND the transformer gets cooler too (very important in amps that work many hours non-stop).  For 600/1000W: big horizontal heatsinks, dual-fan cooled (relatively noisy 220V units, 2/4 times more powerful than 12V PC fans).  The fans pull air from the front or sides  and blow hot air to the back. In theaters and stadiums, nobody hears them.                   

Dear "unprononunceable name" (I wonder why some kids use such meaningless nicknames): your post isn´t very clear. DID you also blow the amp´s fuse? Then you must have blown the power amp: you have an expensive trip to a service shop ahead. If not, probably you just messed the return jack contact; try a short plug-plug cable from the send jack to the return jack. You have a cheaper trip to the service shop or perhaps you *might* be able to replace it yourself. Good luck.

The bridged datasheet application works very well. You have to keep very close to the original suggested layout. I built more than 100 of 12Volts, 20 W RMS "Callejeros" (literally "Street Men") 3 channel combos, with a 4 ohm, 10 inch speaker and a piezo tweeter. The "Super Callejero" is biamplified, with an extra TDA2003 driving a LeSon tweeter. The power supply is a built-in 12V 7A.H. alarm gel battery.

It will work. To check phasing, build a series-lamp fixture , and connect  there both primaries in parallel (label them to be able to identify the primary phase) and the secondaries in series (no load). If you measure 36Vac end to end, fine, label them accordingly; if reading 0 or very close to 0 volts, invert one of them. Good luck.

Dear Muttomatic: ¿+43VDC on the speaker output?  = 99%: Q4, 5, or 6 shorted. 5 %:R16 open. You can replace your expensive MPSU57 by a cheap Tip30 or BD140 depending on where you live.

Short reply: if possible go straight to an LM3886, powerful enough to play live with a drummer.
Transformer: Volt rating: .707 x rail VDC. Example: for +-30V rails, 30x.707= 2x 22V (assuming a small diode loss). VA rating? : at least 1.5 x RMS power output, preferably 2x. Your 160VA units should be fine for a 60/70W power chip. The Jensens are great.

Dear Paelgin, many many thanks for sharing. It´s great to have, now and then, a "modern", "commercial" example of what's really being done today. I get tired of the endless tube schematics, boringly similar or identical, which can be found everywhere.   Thanks again.