positive voltage on heaters

[groovtubin]

Found this lookin at schematics, the mayer amp got me t athinkin @ it, this just popped up. hope it helps everyone!

jim@Omega

[bluesfendermanblues]

Very cool.

Inspired by the Mesa Boogie MKIII, I've tried DC regulated heating on preamps, but never found it worth the while. If you use the gournding scheme from eg. #124, you'll get a pretty quiet amp.

Even in a high gain Soldano x88 DIY, I never found hum to be a problem. Hiss on the other hand, can be an issue with higher gain amps, stemming from tube gain and maybe carbon comp resistors.

[markr14850]

I can't stand hum, so I like DC heaters. In my (small) experience, they are definitely better than elevated+balanced AC.

I haven't heard any difference when trying to elevate DC heaters. Has anyone found this to be sonically beneficial? I suppose it might have to be done if using cascode or cathode follower circuits, where a cathode is at a high potential.

[FUCHSAUDIO]

DC filaments is cool. Elevating is not really needed, unless you have cascodes or cathodes very high above ground (like over 100 V). The newer 12X7's (from Russia in particular) seem to not be able to tolerate the differential. In a Bassman/Marshall circuit or a PI, they die more often than a
Ruby Chinese would.

If you have a balanced line (hum balance pot or accurate balance), lifting don't do much.

[paulster]

DC filaments, done properly, are demonstrably quieter than the best AC heaters, and have the advantage that certain new production tubes (thinking Tung Sol 12AX7 reissue here) that are prone to noisy heaters caused by their construction can be used without issue.

The trouble is that to do it properly is way more effort than doing AC well, and doing it badly will usually yield results worse than even a ham-fisted AC setup.

I'm a proponent, but I wouldn't generally recommend using DC unless you go for a properly regulated solution.

[David Root]

+1 on the regulation, paulster, especially 12VDC. I have used both 6V without regulation (2 x 10,000 uF caps w/choke in between) and 12V with a TO-220 package regulator.

I even put regulated 12VDC on the 12AX7s in the #124 I'm building now.

I became a believer some years ago when building a high gain amp using 6SL7 octal pre tubes, which like all octal pre tubes do not have humbucking heaters, it was a non-starter, hummed like a beehive on Saturday nite....

[Structo]

On that Oddwatt schematic, what purpose do the three diodes serve after the bridge rectifier?
Is that to drop the voltage?

[groovtubin]

On that Oddwatt schematic, what purpose do the three diodes serve after the bridge rectifier?
Is that to drop the voltage?

http://www.electronics-tutorials.com/ba ... supply.htm

here`s a decent tutorial

[FUCHSAUDIO]

On that Oddwatt schematic, what purpose do the three diodes serve after the bridge rectifier?
Is that to drop the voltage?

Yup, .6 volts each.