tube preamp...opinions

[SY]

Simple is better. fscarpa's idea is probably more suitable for your application if you're still getting your feet wet with tubes.

I'd probably try the 165V circuit first- you don't really get much benefit to going higher if all you need to swing is 3 or 4 volts (things are a different story when you have to swing 30 or 40V!). And the 6DJ8 will be in less danger. FWIW, I use a 6DJ8-oid in my preamps with a 150 V supply and it works quite well. At under 200V, components will be cheaper and more compact.

Make sure you get a REAL 6DJ8/6922/7308/whatever instead of a relabelled 6ES8.

[trancy]

thanks a lot federico...

I"ll probably try both versions, and also thanks to SY you are right...actualy I have ECC88 by siemens...

[Jax]

Just a hint:

The plate supply should be delayed until the tubes are heated up. If not, add a diode between the grid and cathode of the cathode follower, diode cathode to the tube cathode. The diode can be 1N4007 or similar.

This will limit the forward bias to 0.7V until the tubes are heated.

I'm using the same topology as fscarpa's myself but with E80CC as gain stage and 6201 as follower. It works well.

[trancy]

Originally posted by fscarpa58
Rout <150 Ohm if freq >500 Hz

THD <0.1% for Vout = 10 Vrms

ciao

Federico

what about running CF on +/- 50 Vdc....

Jax>
****where should I put diodes?


nice snowy day.....

thanks

[Jax]

Originally posted by trancy
****where should I put diodes?

Here:

[DougL]

I ran the Circuit you posted through Tube Cad
to see what general properties it had.

Gain = 20, 26 dB
Zin = 284k
Zout = 721 ohm
F -3dB low = 43.2 hz
F -3dB hihh = 227 khz
PSRR = -11.3 dB
Vmax out = -29/+29.2 v
RL=4.7 k
I = 9.7 ma
C Bypass = 141 uF


The Frequency responce with the Coupling cap Shown into the Zen load is 40 HZ. I am basing the load on the article on Zen amp article in tube cad Journal. I found I had to increase the output coupling cap to 3 uF to get a 10 hz responce calculation.

[JojoD818]

Originally posted by Jax



Here:

I have a 6N1P and a B+ of 150Vdc. Can I try the schematic? Any values to change? I only need it as a buffer.

What software thid you use to draw that schematic?

Thanks in advance,
JojoD

[trancy]

Originally posted by JojoD818


What software thid you use to draw that schematic?

and what kind of formulas do you use to calculate different values of resistors and other, depends on supply voltage?

[fscarpa58]

Guys

download a free copy of Micro Cap 7 demo at
http://www.spectrum-soft.com/demodown.shtm

you will able to draw circuits as well as to
simulate them ( max 50 components)
very user frendly, recommended.

Tube models on the web or ask in the forum.

Federico

[JojoD818]

Originally posted by fscarpa58
Guys

download a free copy of Micro Cap 7 demo at
http://www.spectrum-soft.com/demodown.shtm

you will able to draw circuits as well as to
simulate them ( max 50 components)
very user frendly, recommended.

Tube models on the web or ask in the forum.

Federico

Thanks for the link, I have downloaded a copy. However, I can only see the 12AX7 triode and all others are greyed out. Is this what you mean by tube models? If I'll be using 6922 or 6DJ8, what do I do? Sorry for the questions.

JojoD