Re: [LAD] simulating analog audio devices part II

2007/6/19, porl sheean <porl42(a)gmail.com>om>: The "AX84 P1 Theory Document": http://annex.ax84.com/media/ax84_m35.pdf Noob-oriented introductory document to their simplest SE amp, the P1. ( http://ax84.com/index.php?pg=legacyprojects&project_id=p1 ) The Radiotron Designer's Handbook 4th Edition is online here: http://geek.scorpiorising.ca/RDH4.html The RDH is also pretty noob-friendly (everything you need to learn is there), it's a much longer read though. It starts by the describing the way a valve is made and works up to complex schematics. It's considered by many the "bible for thermionic valves(tubes)". You need an OT with an higher primary impedance IMHO, 6V6 tubes need a higher load to operate correctly. Having a valve load mismatch might have bad consequences for your amp. At an anode voltage of 250V it should be a 5k5 ohm load and at 315V 8k5 ohm according to the RCA receiving tube manual. 4k is a bit low, you'd have to run the tube "starved plate" (at low plate voltages). The sound is usually considered poor when a valve is starved plate. it might be your kind of thing though. If it really is a 4k primary transformer I'd run it at a ~320V B+ and mis match the speaker wiring (old trick) to double the impedance to 8k (much closer to the ideal load)... i.e.: plug an 8 ohm speaker to the 16 ohms secondary tap (or 4 ohms speaker into the 8 ohms tap), that will effectively double the primary to secondary reflected impedance. And this configuration would give you around 5 Watts of power. Thats much cheaper then buying a new OT ;) Also a quick link to a well designed SE 6V6 based PA: http://ax84.com/static/corepoweramps/5W_SE/AX84_5W_SE_Poweramp_Schematic.pdf Some blue glowing is usually pretty normal, I have an 6L6GC based small combo sitting next to me with a blue glowing power tube, and its pretty fine. If I swap this Electro Harmonix tube for a chinese made one the blue glow disappears. You should watch out for any other part than the filament in a tube that are red plating though, now that would be dangerous. Watch out for those big power supply caps! always make sure they're completely discharged before you operate on your amp... potentially lethal voltages inside, as you probably already know. Cheers, -Giuseppe