Beginners Guitar amp project, any suggestions?

[weatherlight]

Greetings

I recently finished my first amplifier project a few months ago. It sounds well, works well. But its kinda heavy (23kg for 40w combo guitar amp) and overdrive sounds are not as pleasing as they would be in a tube amp.

So I decided to build a tube amp. Although I'm an electronics engineer student, they dont teach us about tubes back in the univercity. I'm also a little clumsy but I think I can manage to build a simple tube amp without getting electrical shock :P

I came across this amplifier while browsing the forum. It seemed like a good place to start. The extreme one uses a more powerfull tube at output (or thats what I got) compared to the standart 5w version.

http://www.ax84.com/p1x.html

It has pictures, schematics and some other stuff as well. I want to build a simple tube amp (at least with eq and gain controls however. I saw some junior amps which had a vol pot only :P ). Any output around 8-10W is fine for me. Is this the project to build? Or are there some other alternatives which sound better and are easier to build (more pictures, schematics, building manual, guide etc)?

Thank you for your help

[diegot]

The P1X don't have too much overdrive. You can build the Hi-octane preamp with the P1X output stage.

I will modify my P1X with a 6EA8 for more gain and better overdrive.

[weatherlight]

I just checked the schematics. HO has 3 gain stages (I'm not sure what the cathode folower does, is it just for unity gain? ) where the normal p1 has 2 (which will have less overdirve for sure)

Will this 3rd gain stage add up a massive overdrive? I like to play rock and metal songs with my guitar as well and i dont like mild to low crunch tones too. However I'd like it to be as simple (and cheap as well, i'm on a tight budget ) as I can be. Will the 3rd gain stage make that much a difference?

Thanks

[How_Bout_It]

Take a look at this page: http://www.el34world.com/schematics.htm
About half way down is the 18 Watt Stout. Looks interesting

[diegot]

For sure more gain stage gives you more overdrive.

If you want be simple, go for a pentode/triode preamp.

[weatherlight]

I liked the preamp stage of Hioctane and SEL amplifiers.

http://www.ax84.com/classicprojects.html

problem is they offer an output of 5w (sel offers some more around 8-10 i guess) in class a config. However I could not find KT88.

I would like to use El34 (since I can find them around here) at output stage. I'm geussing it'll provide about 8-10W with class a config (P1x amp at the same site).

What I need is a SEL preamp (3 stages) with EL 34 at output (either class a or push-pull config) I noticed that the B+ voltages are different for the EL34 (p1x) and KT88 (sel). I need to place a El 34 in the sel amplifier. What values do I have to adjust (B voltages? ) to get an El34 to work nicely instead of the KT88 in there?

Also I noticed that the 18w uses 2 EL84s at output. I believe I can find EL84s as well. Can I implement this push pull power amp stage onto the sel preamp? Again what shall be the B voltages, and some other component values when i change these?

I'm new to tubes and as far as I can see, biasing and those b voltages are critical. I dont want to blow the tubes or get a distorted low output. I noticed there is a variable cathode bias mod for the amplifier. Will that do the trick? Please help.

Thank you.

[aletheian]

weatherlight, there is a fantastic discussion forum over at AX84 http://www.ax84.com/bbs/index.php where the project coordinators as well as hundreds of people that have built the various projects and kits hang out to discuss the amps mods and whatnot. You would probably get the answers you need over there from the people that have built them.

[How_Bout_It]

To change from a KT88 to an EL34 in the SEL would only need to change the cathode resistor R9 (430R 5W) to set the bias. To change to P-P would be a lot more work and parts.

[How_Bout_It]

Almost forgot, when switching from KT88 to EL34 you would also need to chang taps on the OT secondary.

[weatherlight]

Originally posted by How_Bout_It
Almost forgot, when switching from KT88 to EL34 you would also need to chang taps on the OT secondary.

Thanks I'll adjust the r9 for optimum bias for EL34 datasheet then. About the taps on secondary, can you explain it a little please? Do you mean the b+1 brown output for the output transformer? And how shall I adjust that ?