Switchable cathode bypass capacitor for Bassman 6g6B

[HommeMarrBuckley]

Hello all

I am new to amp building and was doing a scratch build of a Bassman 6g6-B.
I wasted a lot of time looking at ways to mod the bass channel and have decided it's above my abilities. I am going to keep it stock except for omitting the treble bleed (.005) and was thinking of putting a switch on the first gain stage for different bypass cap values. I was going to use 25uf stock and .68uf.

I am terrible with a schematic and was wondering if anyone here could put the switch in layout format for me considering the original
http://www.gad.net/Blog/wp-content/uplo ... Layout.jpg
...hand drawn or .sch is fine. I read about popping issues, etc and wanted input from someone that would know how to do it correct.

Thanks

[martin manning]

Are you scratch-building a copy or rebuilding your 6G6-B Bassman? Are you free to add an extra eyelet to the board? SInce you are switching the value by more than a factor of ten you can connect them in series or parallel and get essentially the smaller or larger value respectively. What kind of switch are you planning to use, and where do you want to put it?

[HommeMarrBuckley]

Scratch building a copy (have filter cap and rec board finished and have the chassis)

I can manipulate the board in any way fit because I haven't cut or drilled it yet let alone purchased it

In terms of a switch--I dunno would a SPDT work? It's 2 values (25uf / .68uf) with one being the set value

In terms of space for the switch, I am open to whatever would suit best. If placed on the front plate, it would have to go between the bass jacks and bass tone controls (due to spacing issues). The back of the chassis seems like a bad idea with the tubes and the back plate (back left) seems far connection wise in terms of being where it needs to be on the board. Front plate seems like the best idea.

[dobbhill]

Push-pull pot for one of the tone controls: you could use a SPST and put the larger cap in parallel with the smaller cap and avoid swithching noises at the same time..I like 10uf caps-less mud, just me....
YMMV.
D

[dobbhill]

Imagine this: the existing cathode cap and resistor arrangement using a small cathode cap, say a 0.68 or 1ufd. Then, in parallel to that, add another cap, say a 10ufd to 25uf, using a SPST switch in series with the cap to turn it on and off.
Good luck!
D

[Structo]

Along those lines is what I did to my 100w Dumble.

I have a 4.7uF and a .68uF cap.

Connect the positive end of the 4.7uF cap to the cathode pin on the tube.
Connect the negative end to the switch (SPST)

Connect the other lug on the switch to ground.

I put the .68uF on the board as the cathode bypass cap.(from cathode to ground)

Connect a 4K7 resistor between the switch lugs, to prevent hum from the ungrounded cap.

So now in one position I have .68uF (great for humbuckers) and 5.38uF in the other position (good for single coils).

I put the switch on the back panel close to V1.

[vibratoking]

So now in one position I have .68uF (great for humbuckers) and 5.38uF in the other position (good for single coils).

How do you like that setup? It sounds interesting. I don't think you quite have the capacitance that you stated due to the 4.7k resistor. How did you choose that value? I guess what's most important is how it functions. How does it sound? If I remember, 102 and 183 both have about 5uF on V1. This is on the input stage before the tonestack, correct? I am not sure I understand this completely. A 183 with 5uF is not strat friendly IMO. Your mod doesn't really change this. You use 0.68 for the HB side, which is already great with 183, IMO.

[HommeMarrBuckley]

D,

Someone helped me on another forum by posting this. I believe this is what you're talking about.

[dobbhill]

Yessir. You can buy pots with the switch mounted in a push-pull arrangement:
http://www.hoffmanamps.com/MyStore/cata ... G_2249.jpg
From Doug Hoffman's catalog
D