Tube Amps / Music Electronics
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|10/23/1998 11:20 PM|
Could not agree more! I've built amps with regular tansformers, ultra linear transformers High voltage, low voltage and on. Uktra Linear works well with no feedback. I use to build some amps running almost 700 volts and powerfull as hell- they were more sterile sounding than my 400 volt ultra linear designs.
|10/21/1998 12:08 PM|
|Joe K||I don't know if I agree RG|
In my humble opinion I think the harshness on the 135W Fenders is more related to the high Plate volts (500++) than the ultralinear connection. I have mooded my amps for triod mode and like the feel, but they lose a liitle highe end and power. I am going to try an Ultra Linear Xformer because this will put the tube characteristics between "triod" and pentode mode, so I am thinking that I will get back some of the power and high end.
On another Note Allesandro uses ultralinear xfrms in his amps, with good review.
I had a 130 W twin reverb that was harsh, but it was reaaly tight with a big muff and very very clean on its own.
Just some food for thought.
|10/21/1998 12:09 PM|
|Joe K||Sorry about the spelling above, in a hurry|
I goofed up "triode" and a few others, sorry
|10/21/1998 1:43 PM|
|R.G.||Re: I don't know if I agree RG|
Harshness lurks lots of places. High plate volts pretty much means low idle current to keep dissipation in line, and puts the amp closer to the "B" side of "AB" biasing, which implies more trouble with crossover distortion products, so that's not an unreasonable thought.
Triode mode definitely makes for lower power and looser response, probably some treble loss, so your experience matches the profile of what I expect. My experience is that tone is worth lower power.
Ultra linear is more linear, less distortion than either pentode or triode. Put that with a feedback loop, and you get a very linear (low distortion) amplifier, and one that remains pretty linear out to where it starts to clip. This is a reasonable step toward solid state amplifiers too; the linearity and feedback help remove the softer transistion into clipping that distinguishes other tube amplifiers. The amp stays cleaner further out on the power curve. Very good for hifi, and you'll find most tube hifi's using ultralinear. A good tube preamp section or distortion box overdriving the input can sound good through a very linear amplifier, as the amplifier remains neutral until begins clipping; the input overdrive wipes off those pesky peaks that might overdrive the power section.
I encourage you to mess with ultralinear, just as I encourage you to mess with amps in general. More knowlege is almost always a better thing.
Ultralinear doesn't always mean bad.
In the few cases I've messed with on the 135W Fenders, the owners liked the sound better with the tubes taken out of ultralinear in into a mixed pentode/triode; of course, they were guitar players, not bass players. The 135 - in ultralinear - is popular here with bass players that can't get SVT's.
I appreciate the thought-food, and as a position, in my humble opinion, your humble opinion is worth as much as my humble opinion.
|10/21/1998 6:12 PM|
The triode connection should be the most linear of the three types of connections possible with a pentode/beam tetrode. The ultralinear connection was dicovered to try to get "close" to the linearity of the triode connection as well as "close" to the output power capability of the pentode connection. The high end on triode mode is reduced because the effective elimination of the screen grid results in more inter electrode capacitance. The output impedance of the phase invertor in conjunction with the grid stopper resistors will roll off the high end and reduce bandwidth. The pentode mode has higher bandwidth and more power output but at the expense of linearity. The ultralinear puts the plate curves in between where the two other modes are in terms of operation. People who like Ultralinear feel that it gives the best of both worlds (better linearity than pentode, better power than triode) people who don't think it is a compromise at best. All of this was explaned in early '97 issues of stereophile, complete with references and plate curves.In addition the output impedance of the ultralinear connection is between triode (low) and pentode (high, almost constant current. The bandwidth also follow this principle.
Negative feedback will increase steady state linearity as always, independent of the hookup. I should mention that the hardcore Hi-Fi people run triodes with NO feedback loops, so this should be an indication of their inherent better linearity.
Hope this helps, and maybe generates some added thought from others.
|10/21/1998 7:38 PM|
Yup. Been there. I have a copy of Halfer and Keroes' original article in Audio Engineering from the early 50's, they go through pretty much those same points. I also do tube hifi for my home listening, although I don't like to say that in mixed company. - both sides think I've been seduced by the dark side.
I've been pretty thoroughly through the formal, informal, guitar and tweako schools of tube use.
I got a kick out of reading the raging debate in the hifi world in the 50's over the merits of the triode versus pentode, as bad as the tube/solid state stuff of a few years back.
Pentodes' higher gain sensitivity and power capability let you design higher gain and bandwidth amplifiers that can correct the output impedance and steady state linearity down to the triodes'. Triodes without feedback often leave speakers underdamped, so they pop in their own colorations more than with other variations. I don't know of any hifi pentode output amps that don't use feedback - the speakers would be very underdamped.
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