champ with bridge rectifier help please

[tubescent]

i am sorting out the layout for a champ with a bridge rectifier and wondered if one of the more knowledable could cast an eye over what i've done so far please.
i also want to use just one switch for off/standby/on functions and that is where i have really become a bit stuck.

would really appreciate a bit of help as is my first build.

[Steve Conner]

To get off, standby, on with a single switch, you need an unusual switch. What Carling call "progressive": http://www.carlingtech.com/pdf/cirdiagrams.pdf

It can also be done with a double-pole, double-throw, centre off, but it's a bit clunkier, because you have to go through "off" to get from "on" to "standby".

You don't *need* standby.

[tubescent]

thanks for reply steve - yeh i think i'll just wire up a normal on off switch and then change it when i can get hold of one of those progressive switches.

could you or anyone else who knows stuff please cast your knowledgable eye over the power section/bridge rectifier as i was really flying on the seat of my pants as i couldn't find an exact layout to copy for this.

[Steve Conner]

I can't see anything wrong with the way you wired the bridge rectifier.

[tubescent]

thanks again steve.

[loudthud]

A couple of mistakes in the layout. Pin 3 of 6V6 shouldn't go to "A" it should go to the output transformer (blue wire usually). Red wire of OT goes to point "A". The two 100K resistors on the 6V6 socket aren't needed because the transformer has a center tap on the heater winding. Pin 5 of the 6V6 needs to get to the top side of the cap that is connected to pin 6 of the 12AX7, add a wire over or under the board. One of the 220K resistors on that wire is not needed. A 1 Amp fuse is usually all that is required when 240V mains are used.

[tubescent]

thanks loudthud really really appreciated

[ThermionicScott]

The classic BF Champ (and its ancestors) doesn't have grid- or screen-stoppers on the 6V6, but you could easily add those on the socket, if desired.

[tubescent]

the grid or screen stoppers are the 100k resistors i take it? - i'm new to all this remember so need to check everything ; )
i only want to use what works and sounds good ie. not fussed about blackface fender conventions if i don't need them as the design is already a bit off traditional.
will they add anything extra? less noise? i'm just guessing now...

[ThermionicScott]

the grid or screen stoppers are the 100k resistors i take it? - i'm new to all this remember so need to check everything ; )
i only want to use what works and sounds good ie. not fussed about blackface fender conventions if i don't need them as the design is already a bit off traditional.
will they add anything extra? less noise? i'm just guessing now...

If you look at some other BF schematics (like this one), the grid-stoppers are those 1.5K resistors on the control grids and the screen-stoppers are the 470-ohm resistors on the screen grids. No, you probably don't need them, but they do help quell oscillations. The screen-stoppers also improve linearity and help extend tube life.

- Scott

[Bruce / Mission Amps]

the grid or screen stoppers are the 100k resistors i take it? - i'm new to all this remember so need to check everything ; )
i only want to use what works and sounds good ie. not fussed about blackface fender conventions if i don't need them as the design is already a bit off traditional.
will they add anything extra? less noise? i'm just guessing now...

I don't see much of problem with attaching the OT lead to lug A of the B+ rail board.
You'll only see a 10-15v drop there and you'll reap the benefits of extra filtering.
What matters is what is the actual voltage at the nodes and plates.... the current will be rather constant in this class A amp so there won't be wildly fluctuating plate voltages.
And, with that 10K screen node resistor before B, I wouldn't bother using a screen resistor on the 6V6 socket but I would use a 1k5 resistor on the grid of the power tube.
You might that both your 25uF cathode bypass caps on the preamp tube section will be too big (max gain from less then 10Hz on up to ultrasonics) and the amp will sound cool at low levels and super woofy at medium to loud levels.

[ThermionicScott]

Good catch on the 25uF bypass caps. The BF Champ uses a 2uF on the second stage.

[tubescent]

yeh thanks bruce - 2uf now in place.
is this the basic idea with the grid resistors? (i will adjust layout after i check if this is right concept)

[Steve Conner]

Yup, except the one on pin 4 should be 470 ohms per tubeswell's post.

[tubescent]

so this is the deal? really appreciate all your input.