G7 Alternative Heater PSU

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When using 6,3V instead of 12,6V the current doubles. That schematic will only drive 4 dual triodes = two channels of the G7. I would put 100nF caps close to the Vreg in parallel with the lytics. Easy on the output cap, in this case there's no advantage of going that big. You'll only stress the LM317. I'd say it's a hundred times too big :wink: Cold heaters do suck a lot of current! It's pretty hard to kill though. Much better than the LM78XX stuff..

Using a big 220yF cap on the regulator leg makes the regulation worse. 10-22yF with 100nF in parallel is optimum. Good idea to use caps on the diodes. Use a heatsink on the Vreg.

And lower the 470 ohm to 120 ohm. That gives it a harder load, when it's not loaded. It won't regulate/work without a minimum load, usually 5mA.
 
:oops:

i don't think i have fully understand :grin:

- what do u think about the 4 100nf at the rectifier bridge ?

- and what are the 220µF here for ?

the caps values are probably too big, clearly

but 22000µF vs. 10µF for jakob ????? what is the goal
of the last electrolytic ?
 
Btw, why are you going 6V? When I can choose between 6 & 12V I always go with 12V, less current, less hassle. But of course all my fav tubes use 6V :roll: . Are you planning to use other tubes than Jakob? If so, what?
 
The caps across the diodes kill switching noise. Thye not that important with a nicely regulated PSU like that LM317 job.

The 220yF prevents ripple to get into the Vreg, improving ripple rejection with some 10-20dB, getting up to around 80dB total. Too big and the Vreg won't regulate properly or go into oscillation. It'll also take forever to start up.

The cap on the output stabilize the output voltage and lowers the impendance.

All this is explained in nearly every datasheet for a Vreg.
 
SORRY! I keep fukkin' up those numbers :roll: Ok, it's for the mic. Then don't worry about the current :wink:

I've now put a note in my sig, so there's no excuse now :oops: :roll:
 
I disagree with the output cap. When I built the microphone based on the c800g I tried lot of stuff. I was suprised when I added the super caps to the heater supply. Each cap is .033F at 5.5 V for a total of .016F at 11.V. The microphone now seems to have less noise.

I would use UF400x diodes and maybe a low value resistor before the first cap to limit current surges in the diodes if you use low ESR caps. You also need another protection diode in the regulater part.
 
Yes, I agree with you. I had the micpre in mind :grin:

Even better to make an RC or LC filter after the Vreg. I do that in critical amps. You could probably minimize the cap quite a bit if you put the Vreg IN the mic :wink:
 
I'm not too keen on fast diodes, I don't think they make it sound better and their spikes look really nasty on a scope :shock: I use 'slow' diodes/bridges in all my gear.

You don't need that extra diode across the 120 resistor, but it's a good safety precaution.
 
so the 22000µF is better than the jakob 10µF ?

and i'm not shure to have understand the role
of the 470 ? 240 ? 120 ? resistor... sorry :oops:

i think it's time for me to read a Vref pdf... :?
 
Try an emitter follower with a big cap across the base resistor. You can loose those big computer memory caps then.

See:

http://sound.westhost.com/project15.htm
 
Just think of the 120 ohm + trimmer as a voltage divider across your regulated 6V, with the junction going to the regulator leg. The lower your 120 resistor is, the more it's gonna load the Vreg. And it has to be loaded a little to work. Usually there needs to be a load of 5mA all the time.

Read this (page 8&9):

http://cache.national.com/ds/LM/LM117.pdf
 
Heater voltages can easily turn into science, especially with directly heated triodes. It can be very tricky to get right, trust me :shock: It's not just a lightbulb :idea: Tube mics are bitchy too. I'd follow some of Gus' practical experience fer sure.

Gus did you try to vary the heater voltage, to see if it effected the sound?
 

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