New Build Schematic

[Elbowselbows]

hello,
I have been reading and scanning through threads here for a while learning anything a can. I just recently registered to add to threads as well as get feedback on my own projects. I've been doing simple mods and simple builds and this is next.

here is a schematic I did to use up some transformers and parts I already had. I was trying to keep the component values as standard as I could to be tweaked later.
I used ExpressPCB to draw it up.
two 6l6's
split load PI
the tone stack is fed from the anode rather then the more common cathode follower to free up a gain stage for a cold clipping stage I would like to tweak in later.

[IMG773]http://i947.photobucket.com/albums/ad316/mattelbows/Amp-10-preamp.png[/img]

[IMG773]http://i947.photobucket.com/albums/ad316/mattelbows/Amp-10-output.png[/img]


I was just hoping for some feedback or advice on the values and design.
thanks

matt

[Elbowselbows]

nice!! it worked!!!

[Elbowselbows]

Ugh,
I can already see stuff I missed....
The gain pot isn't connected right .. I'll change it next time around. Also I don't know about the tone stack ?

[Gaz]

Maybe you just drew them wrong (with the grid stoppers after the grid load resistors), but you will need some voltage dividers between the stages or you will get a lot of nasty blocking distortion.

[10thTx]

I am thinking that you may need to change some of the values of the coupling caps to something lower & the 47uf cathode cap to something lower?

See the attached schematic (not my design) as an example for comparison.

With respect, 10thtx

[John_P_WI]

Your concertina splitter needs a big ass grid stop. Concertinas sound terrible overdriven and you have a bus load of gain in front of it - you'll also need a lot more interstage attenuation. I would look at the CAE for inspiration of this front end topology.

[Kagliostro]

Give a look here

http://www.el34world.com/Forum/index.php?topic=12774.0

http://www.mediafire.com/view/7qkr82aq9 ... roject.pdf

K

[matt h]

(deleted)

[Elbowselbows]

ok, thanks guys,

k, changed some values and added stuff too!

Gaz- thanks, yup , forgot to put in those dividers. thanks

10thTx - k, made that bypass cap smaller. I copied that stage from a bass amp schematic that used a tone stack from the plate and I didn't know if having that big cap was an important part of that circuit. Guess not. and I didn't see the link for your schematic.

John_P_WI - I put the grid stopper in there. I was thinking of adding another 1M pot there instead maybe just to see what value to use, or as a different volume control. I couldn't find the schematics to the CAE od100 right away , seems hard to find, I'll try again later.

Kagliostro - thanks for the thread link, checked out the AFD mods and all the tips in that tread, interesting!!! A lot of the values for the schems are the same as mine but it looks to have the Cathode Follower . I can also only use 3 preamp tubes because I'm re-purposing the transformers and it has limited current.

matt h - yup, I was afraid too, the voltage dividers should attenuate the gain as well as the cold clipping stage i added??


I changed the 4th stage bypass cap to 4.7uf, changed the 3rd stage cathode res to and bypassed 39k for a cold clipping stage to cut some gain, added the voltage divider to the 2nd stage and and drew the gain pot up right to form the variable voltage divider for the first stage.

Also added the grid stopper to the PI driving stage.

[Elbowselbows]

10thTX - I see the schem now. I'll take a closer look , thanks!!!

[Kagliostro]

Here there is something other you can be interested to see

http://www.el34world.com/Forum/index.php?topic=15609.0

K

[Elbowselbows]

revised edition.
going to try it soon. i'll get some pics soon too.


[IMG773]http://i947.photobucket.com/albums/ad316/mattelbows/Amp-20-preamp.png[/img]