A friend of mine's got one of these, I had to swap output transistors for the right ones (had bipolars instead of Darlingtongs), Tip142 and Tip147, the fact is when a strong signal is applied, volume shuts down. I thought it was a channel switching problem like the one I had with a Roc Pro 1000, but I plug the guitar directly to the PA (using a stompbox to increase volume) and happened the same. Could be a output transistors problem?

Any suggestions will be grateful!

yeah, that one! I knew I had to search in that page, but I never remember it! Thanks Teemuk! Probably I would try some hybrid, tubes and power mosfets.

I'm looking for this schematic... tubes and power mosfets seems to be an excellent combination!

I've read something and some experte made me a comment about it: when you push your powera mp very hard, till clipping section, probably the output will reach peaks of almost twice the total output of the amp. Abouyt efficiency, you'll have to look for 100dB/W/m or higher. For a veeeery reasonable price, I would buy a 75W Eminence speaker, the L1258 (cheapest) or maybe the other 75W, a bit better probabably (I think it was the Black Powder or something like that). They have 100dB of SPL!!!!! Thats a lot.
Peavey Classic series (30 and 50W tube amps) come with a 12" Blue Marvel speaker, made by Eminence, but they have only 96.5dB, not bad, but they also sound dark. New tube Fenders come with a golden label Eminence speaker, but it's nothing but the cheapest 12" guitar series speaker made by Eminence, the L1258. I've got one of those a friend gave me as a gift,  and sounds amazing!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Remember to match impedances, be sure your actual speaker is 8 ohms, so you can use some of the ones I mentioned.

Yeah, but when replace TDA2030, be sure it's a TDA2030A, that A means higher voltage protection. A new tip I learned last week.

Hi! What's the problem with it? If you turn it on and doesn't sound but makes a sound like hum, yor power IC TDA203 is burnt! Just replace it, and voila!

If this is not your problem, we are almost lost!

Well, in fact was simplier than the matter itself! Just one zener bad solder... hehehehehe

It's not a pain in the *ss changing that tube, in fact, is the most simple thing you can do inside one of these! Major problems are pots, changing them will take a few minutes, but taking off the PCB from the chassis needs some patience!

Well, first of all, thanks for these tips! The 16V zener zone on the PCB is a bit burnt, so, I'lll change them, along with filter caps (1000 uf for old 47u, why such a poor filter?). Channel switches but not completly, lights change too (from clean or red overdrive always to green) but, its satyats in the middle. Oh, now you've mentioned it... I think FS jack is damaged. I'm gonna solve this for sure!
Thanks again, you've showed me the way!

Suddenly, channel switching started to switch on its own, and this happens usually when I play at mid output or more, with guitar strumming... could be a faulty capacitor, or switching Jfets went bad? Any help will be grateful.

What about Gibson SS amps? I've tried the G20, with an awesome Ultrasonic 10" speaker I shoked! It waves so much air your pants move! Also I tried with a TS, and sounded excellent. I can't imagine how G30 12" could sound...

I think they-re quite reliable, and I love almost all of them, specially 8040 (80xx series are better than VS, but they do not use the 12ax7 in clean channel), but if you can buy an 8280, try it! Sounds amzing, with a mosfet clean preamp and power mosftes as output... plus stereo chorus!

My first post!

Cool link! I've only listened the K75, and I must say sounds excellent! Really clean!


Solid state rocks! Pics of my amp (yet under construction) in some time.