Kadent 4 ch amp

[gui_tarzan]

Since I couldn't find a schematic for this amp anywhere, and no one seems to have ever heard of it either here or any other forum I inquired at, I decided to draw my own. I'll leave the pre-amp stages for another time, it took 3 hours to draw this much.

The PI stage looks funny to me, maybe one of you can decipher it? I followed the components at least a half-dozen times to make sure the parts are going where they are in the circuit because I'm not used to this type of layout.

I also determined that the first two channels share V1, the 2nd and 3rd have their own 12A*7 tube. That makes V4 the PI.

Any thoughts on this one?

And yes, that's exactly how the filter cap section is configured.

[John_P_WI]

Regarding the PI, look up cathodyne or concertina. I believe Merlin has info on his site, his books certainly do. No surprises there.

[Stevem]

That's how Ampeg does the filter section kind of on some of there 60s amps!

[gui_tarzan]

I don't get why they did a 250mfd in series with a paralleled 40mfd.

[martin manning]

That arrangement is probably not original. The upper and lower caps in a voltage doubler should be matched to minimize ripple.

[gui_tarzan]

From what I can tell it's never been altered, all the date codes are correct ('71/72).

[gui_tarzan]

I am going to change it to a more conventional design, unless I'm missing something I don't see a reason to have the mis-matched cap values. The stock 250, dual 40 and quad 40 are all can caps.

Since it has a SS rectifier I'm thinking using a pair of 80mfd in series (ala Fender) and a 40/20/20/20 can for the PI and pre-amp tubes.

[martin manning]

Miss-matching those two caps is definitely not a good idea. The paralleled 40's on the last node looks odd too. Are you sure you have it traced correctly? Here's what you are showing now...

[gui_tarzan]

Yep, I sextuple checked it just to make sure because it is an odd design, at least to me.

Maybe that's why this model never took off.

[gui_tarzan]

This is more like I was thinking.

[martin manning]

This is more like I was thinking.

With a FWB in place of the doubler you'll be reducing all the voltages by half.

[gui_tarzan]

Huh?

[martin manning]

The original rectifier as you traced it is a voltage doubler, which will result in DC voltage of 2.8 times the transformers secondary VAC. A full wave bridge as in your proposed circuit will deliver only 1.4 times the secondary VAC.

[gui_tarzan]

That might not be a bad thing, if it drops it too much I can use it on a different project.