There has been some discussion rolling about that very same subject, and, in theory, the inverting one was *Very* slightly better (in distortion but more importantly in noise figure) because you "kill" one of the input differential transistors, or, more precisely, ground its base (or gate, if a FET). Anyway, the consense was that the difference is practically inaudible, so, the choice becomes based more in architecture, such as: multi-input or channel mixers become easier with inverting stages (which provide a virtual-ground input) ;    and high impedance stages become easier to build with inverting op-amps, as you correctly suggested.

Those little fans help, they´re definitively better than nothing at all. I once cured a client´s ADA Microtube100 with one of them. Obviously the 1U high rackmount chassis was marginally cooled. When used in stereo driving two 8 ohm Celestions, no problem at all, but when my client started using it bridged driving a single EVM12L, it would thermally shutdown after 1/2 hour of Heavy Metal. No physical space for a regular (80x80mm) fan, so a 40mm, 12V unit was pressed into service: no problems whatsoever in the last 3 or 4 years. I used a W004 Bridge and a 2200uFx25V capacitor. The almost 14dc Volts I get under load have not hurt it so far.

Hi Yustech. I fully understand you, don´t want to cause you any trouble. I think that if you send me, a fellow technician, a copy of the schematic , and we share forces to repair an HK product, that´s an accepted,  "fair use" of said schematic. At most I might extract and post here a part of it and ask you to take some voltage or resistance measurements, then replace some suspect component, to end by repairing it (hopefully). The step by step repair procedure might be useful , at an educational level, for somebody else. Is the power amp blown? Please tell us what was the problem with it.
You can send me the schematic to:   juanmanuelfahey@gmail.com   
Thanks.
JMFahey

Nice Amp, David. Why don´t you post some picture of your speakers, just to see how "thin" the magnets are? There´s an Eminence guitar speaker with a 115 or 120 mm diameter magnet, only 10mm thick, voice coil 38mm, wound on Kapton, which is used by *many* famous makers, including Crate, Fender, Peavey, etc. Probably you have a couple of them; the sound is quite good; of course the V30´s are better (and *much* more expensive)

Hi CasioMax. You´re reading the schematic right. As a general rule, considering it´s a (positive) single supply powered cicuit, polarized caps have their "+" side "towards the chip" and their "-" side "towards ground", either directly or through some resistor. The datasheet schematic is correct. The only exception *might* be C1: 2.2uF, from "Input" to pin "1", *IF* it does not go straight into a passive guitar (which would be a path to ground) but into a preamp which might be leaking some positive D.C. voltage into it. Measure the DC voltage on both pins of C1 just to be sure. Bye.

Dear yustech. Write them (HK), include the serial number; 99% they´ll email you a schematic. Then you post it here and start asking whatever help some of us can give you. ¿Can you solder, read schematics, use a multimeter? Bye.

 Thanks a lot [2]

Does it blow them just by turning it on, or only when playing loud?

Thanks for the link. Very useful. Many of them very oriental, very un-Traynorish. Some of them were made by "Blue Jean Duck" ("vely amelican name") from Taiwan, the makers of many Dean Markleys and quite probably many other "Cheap Line-Famous/Expensive Tag" amps. 2030s are not to be despised, they and their brothers are the backbone of *many* (if not most) practice/home guitar amps today. There is even an "Ampeg" (really a Crate/SLM product), the Rocket 50, that uses two bridged TDA2050 and a quite good 12" Eminence; the end result is quite good and *very* simple.

Dear Darwin. I checked and laughed a lot on Gabe´s site . 99% of his "technical" explanations, are , to talk softly , gibberish .  Anyway, the preamp you built is not bad at all, it´s just a very basic bipolar transistor preamp, input and output buffered by MosFets, total gain around 25 ((15k/500)x0.9x0.9)), flat response, which probably explains your finding it "warm" over the regular preamp from your P.A. Going from 1uF to .47uF doesn´t change the audible response, buy may help in reducing somewhat "pops" and "thumps"  They move upwards the lower frequency limit; the first one from 2Hz to 4 Hz; the second one from 3Hz to 6Hz (approximate values). It might even drive directly an LM3886, please try it and post your results. Keep experimenting, just don´t buy Gabe´s $399, 8 Ft. speaker cable to get a "better, Oxygen Free" warm sound or his "Passive Preamps", a.k.a. empty boxes with a pot. 
Bye.

Hi. I think the copyright holder *in this particular case* can´t have much against you, since a)You´re not printing and selling the "1000 guitar amp schematics handbook" or something similar, which would definitely be a copyright violation, and b)You´re not building an amplifier using the presumably copyrighted schematic, only trying to repair it.
I think that, since usually amplifier factories *do* provide a schematic to help service technicians , either when you buy it or on demand, posting it here , asking for advice or "second opinions" from fellow technicians is well within the "acceptable or allowed use" of said piece of information. There are a few formats accepted by this site, but I suggest that you, if possible, scan the schematic and save it as a 100 to 150 DPI grayscale .GIF , if possible 16 gray. Gifs are much better than Jpegs for  "black on white" schematics or text. Jpegs often make small text (component values) unreadable. Maximum file size: 500Kb.

Hi Michiel. Thanks for our translation services offer, Dutch isn´t easy. I´ve just registered on that site, but, really, I only clicked what I think is "yes" on forms I can´t understand.

I split my PDF into a few functional blocks:

No problem, mail it to: juanmanuelfahey@gmail.com   I do have a schematic and a couple of board pictures, but I want to be sure that we are talking about the same, so when I ask you to measure , say, voltage on Q104´s base or something like that, we agree.

Dear Joecool: I´m up to my ears now with work, but next week I´ll convert my .pcb file into a .gif or .ps , take some pictures, and post them here. The 3886 is bolted to the original heatsink; upside down if necessary, (to avoid touching the original board) and a few short (no more than 10 cm)  cables are wired to the original holes where the old chip used to live : +/-B, ground, etc. I often run speaker wires straight to the speaker itself, to minimize ground loop problems or instability. Basically i replace a "black box" (the original amp) with another.