Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on January 15, 2013, 05:14:47 pm

Title: ADDING A GAIN STAGE
Post by: Colas LeGrippa on January 15, 2013, 05:14:47 pm
Hi everybody !


I would like to add a gain stage to a Champ 5E1. In fact, I did it, but it doesn't work very well. I have reduced the signal by 2 with 2 X 470k, one to gnd and the connection between the 2 to new grid,  added a B+ cap to feed the new 12AX7's plate, put a 10K from new cathode to gnd, and sent the plate signal to the power tube.
I do not want to use an additionnal 1 meg pot, I want to keep it simple.

Thanx

Colas
Title: Re: ADDING A GAIN STAGE
Post by: Willabe on January 15, 2013, 07:07:41 pm
Alvin try a 12AT7 or 12AY7 or 5751 or 12AU7. That will lower your gain.

Tubenet, Geezer, Dummy Load (Pete) and others do this all the time.

If you have 4 gain stages before the power tube you may need attenuation in between 2 or 3 of the gain stages. Try adding larger value grid stop R's and or smaller grid return R's.

    
                  Brad      :icon_biggrin:
Title: Re: ADDING A GAIN STAGE
Post by: Colas LeGrippa on January 15, 2013, 07:34:15 pm
grid return = grid leak ??????????
Title: Re: ADDING A GAIN STAGE
Post by: Willabe on January 15, 2013, 07:40:01 pm
Yes.


     Brad     :icon_biggrin:
Title: Re: ADDING A GAIN STAGE
Post by: Colas LeGrippa on January 15, 2013, 07:57:41 pm
thanxxxxx

Quote
Alvin try a 12AT7

love that  hey hey !
Title: Re: ADDING A GAIN STAGE
Post by: jerrydyer on January 16, 2013, 04:25:28 pm
bleed more to ground like 100k to ground, 220k 220 pf in series right before it, 33 k grid res. 
Title: Re: ADDING A GAIN STAGE
Post by: Colas LeGrippa on January 16, 2013, 04:43:31 pm
thanx buddy
Title: Re: ADDING A GAIN STAGE
Post by: jerrydyer on January 17, 2013, 11:10:17 am
i actually meant piggy backed or paralel on the 220k 220pf thing but you get the idea. try the standard 470k470pf then 470k to ground but in your case just lowering the value of that one to ground.
you going to try the cerem mod?
Title: Re: ADDING A GAIN STAGE
Post by: Colas LeGrippa on January 17, 2013, 01:50:45 pm
Quote
then 470k to ground but in your case just lowering the value of that one to ground.

to avoid electrons build up on the + side


Quote
you going to try the cerem mod?

that's for sure ! But not on my super reverb though......
Title: Re: ADDING A GAIN STAGE
Post by: Willabe on January 17, 2013, 02:55:50 pm
Quote from: Colas LeGrippa on January 17, 2013, 01:50:45 pm
Quote
then 470k to ground but in your case just lowering the value of that one to ground.
to avoid electrons build up on the + side

To bleed off/throw away signal to ground so you don't slam the next gain stages grid with too much signal.

       
             Brad      :icon_biggrin:


Title: Re: ADDING A GAIN STAGE
Post by: Colas LeGrippa on January 17, 2013, 03:26:57 pm
common voltage divider
Title: Re: ADDING A GAIN STAGE
Post by: Willabe on January 17, 2013, 04:11:19 pm
Quote from: Colas LeGrippa on January 17, 2013, 03:26:57 pm
common voltage divider

Yes.


            Brad     :icon_biggrin: