The Red Light District - another PP EL84 amp

[Mas Penk]

SY, i'd like to ask fews newbie's questions :
1. Do I really two power supply? Can We just buil one power supply ? Does that will have any effect?
2. If we have to use 2 power supply, the what is the transformer's capacity for the driver? i have one small transformer (270VAC/20 or 35mA without CT). can I use that?
3. Could you explain me why you use regulated B+ for screen grid while you use simple CLC supply for Driver? Because i usually build amps with regulated at driver (even I use DC for heaters) and use standard CLC for Output?

Thanks

Ferry

[EsE]

Ok, sy!
Can I use the AN TRANS-200 (8k 15w)?
How do I adapt the circuit to this?
And not least what spec's do I need for the mains transformer?

If I go for this design, it will be my first tube amplifier from scratch!
I need a design that will give me some good sound in my rf-3's to inspire to continue diy'ing.

[Variac]

Arnoldc's idea is a good and simple one. Even with a conventional chassis, it could have feet say 1 cm tall and the LED's mounted on the bottom in a simple grid on a panel. Then the chassis would "hover" on a pool of red light, like the automobile guys do to their cars. The "look of power" and maybe not so bright as to ruin the pleasure of looking at the tubes/valves.

[jane]

SY,
Do you have any more information about this amp?
What I would like to know is Zo, distortion pattern and more technically things than just the pattern of the red light district LESs.
I can see that you have put in some large grid stoppers that will help in case of blocking and that the forward roll off frequency is quite low (indicates bad OPTs?).
Any comments?

[SY]

Originally posted by Mas Penk

1. Do I really two power supply? Can We just buil one power supply ? Does that will have any effect?
2. If we have to use 2 power supply, the what is the transformer's capacity for the driver? i have one small transformer (270VAC/20 or 35mA without CT). can I use that?
3. Could you explain me why you use regulated B+ for screen grid while you use simple CLC supply for Driver? Because i usually build amps with regulated at driver (even I use DC for heaters) and use standard CLC for Output?

Using a separate supply for the driver lets you run a higher voltage there- good for linearity and stability. And the second supply only neds to deliver 10mA or so, so it can be pretty inexpensive. The transformer you have should work perfectly.

With pentode output stages, the screen supply is MUCH more critical than the plate supply. So regulation is called for. As a benefit, it gives a very convenient way to adjust idle current.

With the driver supply separated and the driver running class A, regulation doesn't bring much to the table.

[SY]

EsE, I don't know that transformer. Is it made for push-pull? If so, it should work.

Jan, there will be much more info in the actual article. Bug Bas about publication date. Regarding measurements, they're in the article, too, but rest assured that I do NOT believe in designing without careful measurement.

BTW, good pickup on the seemingly odd value for grid stoppers!

[Bas Horneman]

Bug Bas about publication date.

I'll aim for next week....

[ErikdeBest]

SY, I have one question about the Maida regulator. I read (probably Morgan Jones) that the current through the zener diode should be at least 5mA for it to operate without producing to much noise. If my math from after 2 in the morning is right, in your design there is about 1,3mA going through the zener. Is that sufficient? Did you try higher currents? What where the results?

Many thanks

Erik

[SY]

The noise from the zener isn't critical in that position, being knocked down by the regulator and feeding a stage that's at 300V.

BTW, I should mention that the amp has less than -100dB noise referred to max output.

[ErikdeBest]

Hi SY Thanks for the reply. Erik