I need a louder 5c3....

[garytube]

Hi all,
I like my Weber 5C3, but I need more volume, headroom. I have a weber power transformer for a bassman, and I have a weber bandmaster/ pro output tranny that are collecting dust. Can I use these in the 5C3 circuit and keep it cathode biased? Looking at a few schematics I think I may need to:
1. use 6L6
2. install 1.5k (2watt?) resistors on the power tube sockets
3. Increase the 250 ohm bias resistor wattage from 5 watts to 10 watts, or more?
4. I see a choke with the pro and the Bandmaster circuits... can I get by without one and keep the 10K 2 watt?

Is this doable without building the whole amp over again? Thanks for any help!

[tubeswell]

I think I may need to:
1. use 6L6

Yep you can - just make sure your PT is at least 180mA on the HT winding (some may say 150mA - YMMV) and 4A on the heater winding

2. install 1.5k (2watt?) resistors on the power tube sockets

Are you talking grid stoppers? or screen resistors?

Screen resistors can go anything from 470R to 4k7. The bigger they are, the lower the screen voltage will be, and the less power you will have. (BTW this isn't going to sound like a 5C3 any more)

Similarly grid stoppers can be 1k5 to 4k7 - the bigger they get the more highs they will cut out, but the better they will be a stopping blocking distortion. But try it without them first and see how it goes.

3. Increase the 250 ohm bias resistor wattage from 5 watts to 10 watts, or more?

Good idea. But stick with either 220R or 250R for the bias (you may even be able to get down to 180R, but see how the tube dissipation is once you have got the B+ up a bit.

4. I see a choke with the pro and the Bandmaster circuits... can I get by without one and keep the 10K 2 watt?

Yep. the choke will change things quite a bit - give the pre-amp a lot more headroom, and you may or may not like that. You will also definitely need to add screen grid resistors if you swap to a CLC filter. It will also sound even less like a tweed deluxe

Is this doable without building the whole amp over again? Thanks for any help!

Yep. You just need to change the OT load resistance to half of what it is for the 6V6s. (So that means plugging 4R speaker into the 8R tap on your OT, or plugging 16R speaker into the 8R tap.)

You also probably will want to put a GZ34 in instead of the 5Y3GT (to get the B+ above 400).

And you may want to chuck another 1 or 2 x 20uF 500V filter caps in parallel with the reservoir cap (to up the reservoir to 40-60uF), but just watch how high the B+ is when you do this. You don't want to exceed your filter caps' max. voltage rating

However even if you do all the above, you may not get it much louder than it is now. This'll be more like a souped-up 5E5 but without the same input stage.

You really need fixed bias output stage and about 460VDC B+ with 6L6s to get noticeably more output power.

[garytube]

Wow, thanks tubeswell! I might have to give it a try. To be honest, if it changes the tone a bit then I don't mind. If I can get the amp a couple db louder, with a bit more headroom and girth, then I'll be happy. One thing I still don't understand is if I'm using the weber bandmaster output transformer that has multiple impedance taps.... shouldn't I match the impedance of the speaker to the tap, or do I still offset?

[tubeswell]

One thing I still don't understand is if I'm using the weber bandmaster output transformer that has multiple impedance taps.... shouldn't I match the impedance of the speaker to the tap, or do I still offset?

That's right, if you're using a Bandmaster OT it will be wound for 6L6 load resistance, so just use the normal taps