6s4a as driver for 6as7 in SEAmp

[alejo]

Hello, I think build one little SE AMP. arround 2.5+2.5 Wrms.

as Output stage I want use 6as7 (one triode * chanel) in this stage no problem.

to drive this I think in 6s4a triode (because I want use this, I find lot in close TV service.-)

The question is, what operating poit for 6s4a to obtein 76V peak (need this in 6as7 grid) ?

plate volt ?; value of katode resistor?; value for plate load resistor?, help schematic for this driver stage !!!

thanks
Alejo

 

[jeapel]

hi
my hybrid amp:

www.loginnovation.com/jeapel

but for 2.5watt with 6as7 just :

1-remove the 220uf + 2uf (dont bypass 600ohm it s more linear)

2-put a transfo in anode maybe 2kohm to 8 ohm

3-maybe jump the 150v to 200v to get the watt you want

very good sound when i try this configuration but with
my hybrid the bass are much better
bye 🙂

 

[Alex Kitic]

6AS7 amps

I have built quite several variants of 6AS7G/6080 amps, with approx. 2.5W per channel. The schematics were never published on my site, mostly because of a lack of time.

Generally speaking, the best sound from 6AS7/6080 can be obtained with highish Ra (like 5-6k primary), adopting high B+ voltage (some 235V thru the valve) and some 50-60mA of current. Such operating point means a bias of approx. 130V, and to drive the tube to full power you will need some 260V peak to peak. It is not impossible, quite the contrary. I usually adopted 5687 as driver tube, and used various ECC8x as input stage.

If interested, let me know.

Regards,
Aleksandar

 

[alejo]

thanks for reply;

Yes Alex, talkme more about yours 6as7 amp !!
I have free two good OPT 5k/8ohms

You have schematic?

 

[jleaman]

jeapel how come in your schematic for your tube amp there is no transformer on the out put ?

 

[jeapel]

alex:
5kohm transfo is very high for a 6as7 is my book
2.5k would de max. and b+=235v and 5kohm
give 1.35 w rms if no error

jason:
"no transfo" yes and it s equivalent to a very good
tranfo and a source follower is neutral only the
"sound tude" is hear
see www.zenn.com.sg/Why hybrid.htm

 

[jleaman]

jeapel Printed and into my book of ideas and schematic's.. Do you have any pictures of your finished product ?

 

[Alex Kitic]

6080/6AS7 amp

I include with this post the schematics of the first version (generally speaking, I mostly did experimentation with input tubes and driver tubes, but this one will most probably be the most interesting, and it might as well not need a preamp, just a selector and a pot).

The schematics looks a little strange, since it was drawn for simulation purposes. Of course, if taking care, an amp can be constructed using this schematics (one resistor is actually the DCR of the primary, etc.).

When it comes to calculus, 235V across the tube (not B+ when you have automatic biasing with a cathode resistor) does not give only 1.3W, but approximately 2.5W (if needed, I can supply the simulation results).

Ra is a little high... but at this current and voltage, if you have the complete datasheet of the tube, you will see that it is far from the 200 ohm internal resistance, more like almost 1k. In that case, you can adopt 2.5x the internal resistance as Ra, but by increasing, you loose a lot less in power as much you gain in (decreasing) distortion... not to mention improved damping factor, which is always a good thing with SE amps (that is why most SE amps are accused of not having good bass -- they usually work into 2.5x the internal resistance of the tube).

Regards,
Aleksandar

 

[jleaman]

jeapel can you email me please..

I have some questions for you ..