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For amplifiers over 30 watts per channel, I prefer DC biasing. I make it so it's really easy to use and set up. The NS-50 offers up to 50 watts per channel. Next, I have 100 watt monoblocks. I can look into 75 watt/channel iron for you if you want. However, just so you know, monoblocks are better suited for this power level. It is better to use four power tubes to distribute the load rather than two when you go above 50 watts per channel. My design has only five tubes per channel (4 Power tubes plus one driver tube). These are DC biased, but as stated above, it's a simple setup. High power amplifiers are my specialty. Either model will operate very,very clean, fast and have superior resolution for digital sources and critical listening. They thrive on demanding movie passages too. BTW: It sounds like the 275's bias wasn't set up properly.
Can you put the amp in a receiver chassis so the wife won't notice?
BlairFor 30W what is estimated cost increase quad EL84 vs. pair of EL34 as we discussed earlier? (Obviously extra labor & parts four outputs vs. two.) For neutral tonality, 85 Hz high-pass bass cutoff & 13 Ohm load as mentioned earlier, how might you describe audible difference quad EL84 vs. pair EL34? Thanks!PS: I may order before the speaker project is done ...Can you put the amp in a receiver chassis so the wife won't notice?
Yes, my DC bias system is adjustable and from the outside with one knob. Adjustments and fine tuning are very easy. No meters necessary! "Is your DC biasing user adjustable?"
I'll tell you something- that $200.00 option is going to change soon. I like it so much that it will be standard equipment on DC biased amps. I will have a price for making an amp 30 watts and under DC biased and leave it at that.How the tunable bias system works: The DC Biasing knob is calibrated to 12 O'Clock for the tubes the amp is sent with. My setting is a tad conservative. That provides 'tuning' leeway for either more or less bias and/or different tube types. It works very,very EXTREMELY well! Amps with this option come with instructions specific to that amp. On top of working extremely well, it's incredibly easy to use. The knob is on the outside. I have placed it on the front of many NS-50's.
Tubes may wear at slightly different paces and that is fine. Most of the time that is not an issue. Tubes are generally biased in pairs, or all together, such as in a Fisher 500C.What if one tube acts up and becomes considerably different than its mate? Then it's defective and should not be compensated for. I do not like the individual tube biasing setup of some amplifiers. It turns people off and there's no need to worry about subtle differences.
Different things bother different people. Those who are used to SS amplifiers or used to cathode biased smaller tube amps often don't like having to constantly mother their amplifier. In fact, this mothering is what turns many people off. I don't blame them. The Tunable Bias setup is a splendid system that many people now enjoy. The main idea is to bias the tubes to run as cool as possible without loosing sound quality. It works perfectly. You may not have thought about this: If someone wants to operate their amplifier at, say half power, the bias control can be set to allow the tubes to run cooler with no ill effects on sound quality. This greatly extends tube life too. I added up the pro's and con's of this biasing approach and found the advantages greatly outnumber any disadvantages. I didn't find any important disadvantages to speak of. A considerable amount of time and money goes into research, building prototypes, testing, etc... Some people are more into the technical aspects of tube amplification. I think you're one of them and that's great. Please keep an open mind to new ideas!
