Solid-State rectifier in a D-Style amp and it's filter caps

[Ibanezgrind]

Greetings!

I am planning on building a TwoR/D-Style style amp minus the reverb section. I wasn't able to find a schematic but a layout was availble. It uses 2 X 200uf @350V in series for the first stage of filtering and 8 X 47uf @400V for the preamp.

I know using a GZ34 is out of the question with such hi capacitance filtering. Since my PT has filament windings for the rectifier tube, I plan on using a solid state rectifier plug in for this tube socket...OR I can just tie off those windings and make the recitifier in layout with diodes on an eyelit board. Does it really matter which way I go?
 
I wasn't able to find any 200uf caps anywhere so far but found 220uf. This small amount more in added capacitance shoudn't be a problem since it's solid state, correct?

The pre-amp filtering has 8 x 47uf which 2 are in series with each other at a time. There are a bunch of 470K resistors connected to them. Is there a particular reason why they did it this way? Why can't I just use 4 X 22uf @ 500V in the same manner as any fender blackface pre-amp? Please check out the attachment straight from the layout I will use.

I am still debating wether or not I want to build this. It depends on what answers I get here that will allow me to proceed (I hope!) or stick with my original amp layout. I apprecaite your time and knowledge! Thank you.

   

[MakerDP]

You use filter caps in series when the supply voltage exceeds the voltage rating of your caps.

The 450k are safety bleed resistors to drain voltage from the capacitors when the amp is switched off. Don't know why they put so many in there. You really only need one, typically on the first filter section.

Does your amp have relays? If so, use the 5V winding rectified and regulated to power 5V relays instead of tying it off. Otherwise, yes you can tie them off but put some wire nuts over the ends or crimp some shrink-wrap onto the ends to prevent shorting it out on something.

[Ibanezgrind]

Thank you MakerDP for your insight.

It sure would be nice to know those voltages coming off those pre-amp filters. It doesn't seem like they would exceed 500V although I see they use 3W dropping resistors. Overkill to be safe? I looked at some other D-stlye layouts and some have 22uf/500V singles instead of whats shown on this attachment. Maybe it would be a good idea to get a cap array like this to be safe or find 22uf caps that exceed 500V.

Since it's a new build I can add relays to the 5V windings. I wasn't aware of this and seems like it's better than just tying it off. I will look into this. Thanks again!

[MakerDP]

The specs of the power transformer will give you an idea of the voltages on the series caps. But even if they were right around 450V, it would be safest to do the series thing to get some wiggle-room, especially seeing as how your typical high-voltage EL capacitor has only like a what, 40% tolerance or so?

Just curious why you are choosing this layout. Are you aware there are extremely accurate and well-tested D-layouts out there?

[sluckey]

The 450k are safety bleed resistors to drain voltage from the capacitors when the amp is switched off. Don't know why they put so many in there. You really only need one, typically on the first filter section.

The resistors do drain voltage when switched off. But that's just a bonus side effect. The real reason is to insure the series caps charge to equal voltages. You will need two equal value resistors for each series pair of caps.

[MakerDP]

ah yes I had forgotten that... thanks for clarifying!

[Ibanezgrind]

Thanks for your replies guys! MakerDP, do have any resources where I can find these D-style layouts? I know of only Ceriatone's stuff.

[sluckey]

Go to TAG...


     https://ampgarage.com/forum/

[MakerDP]

Go to TAG...


     https://ampgarage.com/forum/

Yeah, this.

TAG is the repository of all D-knowledge. Several layouts, schematics, build support and from time to time people offering complete eyelet board sets and pre-drilled & silk-screened chassis.

[Ibanezgrind]

Thanks guys for letting me know about TAG. I found exactly what I was looking for!