[civic]

hi to all

i am looking for a good schematic to build a guitar amp with a 6au6 tube for the preamp
can someone help me please

[SvR]

Hi,
I don´t know a guitaramplifier with a 6au6, but it gives some schematics for amplifiers with EL34 and 12AX7 like this http://www.ax84.com/static/p1x/AX84_P1x_080623.pdf or this one http://www.tube-town.net/diy/tt66/tt66.html.
I think one Pentode hasn´t enough gain for the tonestack and the EL34.
mfg sven

Sorry for my English  

[zaphod_beeblebrox]

Hi, IIRC
Ub = 400V
Ra = 38k
Rk = 330 - 380R

gave an good inputstage.

Do you want SE or PP Outputstage?

Best regards,
Matthias

[sjhusting]

The 6AU6 amps I have found all drive smaller tubes, mostly 6AQ5 (various Univox). Without going into detail, I think Sven may be right. You also want to be able to drive the EL34(s), and if a single 6AU6 is used to drive a  6AQ5, I'm willing to bet it won't swing enough voltage to drive an EL34 as hard as you would want in a modern amp.

You might want to look at EF86-based amps and see how they are designed, substituting a 6AU6 shouldn't be a big deal

steven

[darkbluemurder]

Hi,

You may want to check the large discussion thread on the Hoffmann-Forum on the HoSo56. The thread title is "New EF-86 project - design input sought". Somewhere in the thread there is a discussion about various pentode types, including EF86, 5879 and 6AU6.

That would of course be more than just a simple pentode preamp. The topology would be pentode - gain control - triode gain - cathode follower - tone stack - long tail PI- power amp. I built an amp based on it and it sounds great.

You may also want to check out this
http://www.schematicheaven.com/newamps/matchless_clubman.pdf

Again a different topology: parallel triode - tone stack - pentode - volume - long tail PI - power amp.

This amp could be built with a 6AU6 instead of the 6SH7. In the Ampage forum I stumbled across a thread where one guy built one with a 6AU6 using a 100k plate resistor, a 680k screen resistor and a 1.5k in parallel with a 25uf cap on the cathode. I haven't built one myself so I cannot comment on the tone but this is on my project list (likely with a 5879).

Greetings
Stephan

[sjhusting]

You may want to check the large discussion thread on the Hoffmann-Forum on the HoSo56. The thread title is "New EF-86 project - design input sought". Somewhere in the thread there is a discussion about various pentode types, including EF86, 5879 and 6AU6.

That's it! I knew I had seen a newer design somewhere.

Some of the Bad Cat amps use an EF86 with EL34, but they are newer designs for which I haven't seen the schematics yet.

steven

[civic]

thank you audio friends for the advice
i will go for the ax84 project