Gibson GA-40 Layout - No tremolo

[MHProd]

Can you guys this is correct? I found the layout online and took out the tremolo. Tried to double check with the schematic but I want to make sure I'm not missing anything? Looking at building a 6L6 version.

Thanks!

[Stevem]

Go look at the shematic for a GA20 .

[MHProd]

Tried that. Can't find the schematic of the ga20 with noval preamp tubes.

I removed the tremolo from the layout as you can see. I just would like a second opinion.

[tubeswell]

The GA20 has pentodes in v1 on each channel in the preamp - just like the GA40 does. All you need to know is the pin-out for the type of pentode you'll be using (consult that tube data sheet)- doesn't matter whether its a noval base or not. The screen will be on the screen pin, and the plate on the plate pin etc.

[MHProd]

Not that good with schematics I'm afraid... Looking at both, the circuit and values seem to differ quite a bit.

The full layout I posted looks good to me. Not sure if I removed the Tremolo properly though...

[Stevem]

If your just starting out at reading schematics I would suggest you go to the AX84 site and build a P1 version with a 6L6 output !

[MHProd]

Thanks for the suggestion but as I stated, the GA20 schem isn't quite similar. I guess my main interrogation is the 510K/.01uF on V2. The cap goes to the plate and the resistor to ground. I don't know if I should keep the resistor or just wire the cap directly to the pot. Looking at the ga20 schem, I don't see a resistor/cap arrangement on V2.

[Stevem]

Your hell bent on doing this I guess?
Here you go!
The 10k resistor above the depth pot is the power supply dropping resistor that feeds both pentode off of that 10 uf filter.

See how that filter feeds that 100k and 750k resistor on channel 1.

The 1 meg pot to the right of the string of Tremolo caps is still going to be your channel 2 volume pot.

The 100k resistor above that pot is going to be your mixer resistor, so to start off with change that to 470k just like the mixer resistor on channel 1.

Now build up your channel 2 just like channel 1 and power it's plate and screen off of that 10uf filter.

For a different sounding channel with adifferent gain level you can go up or down in the value of its Cathode bypass cap by 50 to 100% if you like.

You can go up or down in the value of the 33k Cathode resistor by 20%.

The plate output coupling cap ( .01 ) can be taken up or down also by a huge amount depending on how much bottom end you want and how much farting out you can tolerate out of the speaker when the amp is cranked!

Note that I would strongly concider adding another 10uf fikter across that current 10uf after the power supply choke!

[MHProd]

Thanks Steve!

Yes, I'm planning on upping the filtering. 30uF on the mains 20uF everywhere else.

I'll tweak some of the preamp values from there. Still not sure about the 510K between ground and the .01 cap on Chan2. I guess I could try both ways. Not a good idea to keep the mixer resistors to 470K/100K?

[tubeswell]

... Not a good idea to keep the mixer resistors to 470K/100K?

If you want a balanced set of input channels, the mixing resistors ideally should be the same for both channels. (I take it your idea is still to remove all the extra AC loading in the 'ex-vibrato' channel - as part of removing the vibrato circuit?).

[MHProd]

... Not a good idea to keep the mixer resistors to 470K/100K?

If you want a balanced set of input channels, the mixing resistors ideally should be the same for both channels. (I take it your idea is still to remove all the extra AC loading in the 'ex-vibrato' channel - as part of removing the vibrato circuit?).

What do you mean? Didn't I do that already in the second layout?

[tubeswell]

... Not a good idea to keep the mixer resistors to 470K/100K?

If you want a balanced set of input channels, the mixing resistors ideally should be the same for both channels. (I take it your idea is still to remove all the extra AC loading in the 'ex-vibrato' channel - as part of removing the vibrato circuit?).

What do you mean? Didn't I do that already in the second layout?

I talking about the mixing resistors. I.e. suggestting you keep them both the same value

[Stevem]

You do not need any of that term circuit parts, all you off of that last 10uf filter node are the two 100 k resistors to feed each plate.
This why I said start off by building it like another Channel 1.
Mixer resistor wise you should be fine with having one of the two channels going thru a 330k resistor if you want one channel to be louder and clip the output section faster.