Vacuum Tube Amps

Sooo.... what about leg room?  I'm sorry, I'm a bit ignorant.  Can you elavorate a bit more or is there a site were I can read some more about this.Poly Dollies

Wrong... not completly, but mostly. The voltage across a speaker's terminals does NOT equal headroom, unless the power supply for the amplifier can provide the current necessary to MAKE the power by maintaining the voltage. That is headroom. Voltage without current is NOTHING (sometimes known as static electricity). With the exception of VERY high end, highly esoteric home amplifiers, with DOZENS of output tubes - so as to be able to provide current without a transformer, EVERY tube amp utilizes an output transformer, to convert from high voltage/low current (which is what the tubes output) to lower voltage, higher current (which is what a speaker needs to function). In this particular amps case, the primary voltage is 300, but the current can only be 60mA, which would NEVER be able to drive a 4 ohm speaker directly - well, it would, but not to very high output levels... In order to make 18 watts across 4 ohms, you need 2.1 amps, and 1.5 amps at 8 ohms. You can do the math here, and see that I am right. A transformer does not MAKE power, they convert power - if 18 watts comes out, then AT LEAST 18 watts must go in! ( I say at least, because there will be some losses in the transformer) I noticed that you have a "custom built 40 volt pre-amp". Is this where you got the idea that voltage=headroom? I hate to tell you this, but you may actually have higher distortion from your pre-amp than I do from my head unit, because, unless you are attenuating that 40 volts to a level that most amps can use, you are NOT running your pre-amp output devices in their linear range. EVERY amplifier (pre, power, low gain, high gain, RF, audio) has a distortion curve, that has its most linear range (lowest distortion) usually between 25 and 50-60 percent of it's maximum output design. If you are running this pre-amp in it's low non-linear range, (below 10 volts out) you MAY have spent money on that pre-amp for nothing. Here is a page to read up on it for yourself. See diagram 8 on page 8. (This is the best representation of what I am trying to explain I could find.) Granted you will likely have a MUCH lower noise floor, because your amps can be turned all the way down, and still be driven to full output, but I am referring SPECIFICALLY to distortion, not SNR. Anyway... I just wanted to chime in...It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

haemphyst, you so smart. The level of knowledge on this forum astounds me sometimes. I have read a few other forums but didnt even bother joining because no one seemed to know their ass from a hole in the ground. On this forum you get complete explanations like that all the time. And by the way Office Space is one of the finest movies of all time. Everyone should see it.double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer

lol.......the BOBS99 F-one fitty

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Haemphyst- Not EVERY tube amp uses an output transformer, there OTLs out there (output stransformer-less) but they use tubes specially designed for that kind of duty, lower supply votages, and much beefier grids and anodes, to handle the greatly increased current. ;-) All- Also, to add a little more to the supply voltage != output voltage, the tube supplies are only at a few mA. With the 18W 4 ohm example, that 300V tube supply is only being asked for 120mA (0.12A) at maximum output, assuming it's 50% efficient end to end. I'd also bet that anyone trying to use one of those amps in a car for anyting below 100Hz will have a problem, due to the size of the transformers used. Small output transformers have real issues making bass, due to a variety of factors, but mostly because small transformers saturate easily at low frequencies. It's the same principle that makes switching supplies so popular these days. As far as their cleanliness...I'm suspiscious. I've designed and built amps of all varities, and for the parts cost on those amps, I'm not sure they can do much better than break even with an average solid state amp. Although the tubes seem to be running in their ultralinear range, they will dissipate a fairly large amount of heat, become microphonic quickly, and will grow noisy after a short while due to the physical abuse they take, independent of any shock suspension system. The only real advantage tubes have in this kind of application is that they are forgiving of being overdriven to a small degree, as their clipping behavior is 'soft'. They sort of mush around instead of clipping with sharp corners, and the resulting distortion is mostly 2nd and other even harmonics, which humans find to be pleasing to the ear. Tubes can be extremely linear and accurate, but for my money, I can do a lot better than phsae shifting transformers, vibration sensitive, cycle intolerant glass bubbles in my car. That said, I love the EL84 practice amp I built for my bass, and the tube amps I use when recording bands, but I'd put neither anywhere near a critical playback system. I'll leave them to applications that need color or high power RF amplification. And as for Wiseguy's IEEE citations, I've been a card carrying member since 1995. Those articles, while well written, are definately the product of a very small subsection of the industry, and should not be taken as gospel. -daveThis is not a sig. This is a duck. Quack.