Why Are 12A*7 Tubes So Bad?

[SY]

sajti, yes, a CCS is even better. BUT... you have to account for the resulting high source impedance. It's all a matter of doing the engineering rather than relying on legend. I plead guilty to the latter, but once I actually investigated, I was pleasantly surprised.

 

[SY]

Johnny, that will give you fairly high 3rd and 5th harmonic. You might want to look at the comprehensive distortion measurements on medium mu triodes in Morgan Jones's "Valve Amplifiers."

 

[Miles Prower]

This is what my inverter looks like now... Pretty Basic.

A little too basic. It'd be better with an active tail load. That way, you wouldn't need to force balance with the unbalanced plate resistors. That might also take care of the h3 and h5 problem as well.

 

[sajti]

sajti, yes, a CCS is even better. BUT... you have to account for the resulting high source impedance. It's all a matter of doing the engineering rather than relying on legend. I plead guilty to the latter, but once I actually investigated, I was pleasantly surprised.

Of course. But this is the price of the high gain. I think that 12AX7 is good for preamplifier application only. In my power amplifier I use E88CC and ECC99 to drive the 6550s

sajti

 

[JandG]

I have no love for 12au7, but seems in some circuits it does not matter. I have a old Ampex pre that uses them w/ 12ax7, it sounds good. Also in many tuner's Mac etc..which also sound great. My Scott 299B has a row of 12ax7 in front end, albiet all Mullard loaded, but it sounds far from bad. But to be fair to the haters of such things, I run all oldies for reason of they sound superb. 26, 27, 10, etc....Also I do remember running a hot rodded Basie that had 12au7 in it, when I swithed to 12BH7 that showed me right then & there that 12BH7 lays waist to 12au7..at least in that circuit. Also My Soldano & Marshalls of old have 12ax7 in them & they make better music than any hi-fi system...*s*
J & G

 

[SemperFi]

Yes, but only if You keep the anode load over 200kohms.

sajti

Yes but that's the thing mentioned earlier; you must use different tubes in appropriate circuits and they will function very nicely. If you simply throw tubes into generic circuits you will find some are better than others, but thats b/c the circuit is not optimized for that tube.

 

[mashaffer]

Sounds like the makings of a good shoot out. Call it the crappy tube shoot out for the designer who is getting board with building those nearly perfect amps with all the right tubes. Something like this.

For simplicity all entries could be integrated amps. The design constraints would include a list of tubes which are considered poor tubes for hifi use. Each amp would have to be built using only tubes on that list.

Then put together a panel of musicians and other qualified listeners to judge the amplifiers using a test setup where the judges can not see the amplifiers under test.

As a control you could have one amplifier designed with boutique tubes.

Watcha think.

mike

 

[ChopperCharles]

12au7

Out of curiosity, if I replace the two 12AX7's in the preamp stage of my integrated amp with two 12au7's, other than reduced volume how will the 12au7's affect the sound? Will I get more bass? Reduced gain isn't an issue, the Vegas are 102dB efficient and the volume dial is barely turned before the speakers are at normal listening volume.

If not 12au7's... what tube would you recommend for some extra bass? (Or should I consider different KT88's or 6n8P's?)

Charles.

 

[ashok]

ChopperCharles :

You've missed the point again. You cannot pull out a 12AX7 and plug in a 12AU7 and expect it to work well. Both work best at different operating points ( anode current and voltage ) and with specified loads.

If you need to use a 12AU7 you will have to make changes to component values also. While the -3db point for LF will be determined by the capacitors the actual sound can be determined only by buliding it.