Originally Posted by FallenAngel
Resistance between the secondaries is around 32R.
If it is 32R from CT to each end, you can reduce the two 33r to 10R or 22R. If it is 32R from the extremities, keep 33R.
I already have a 100uF/400V cap for each channel as per amp schematic, should I replace it with a 220uF?
Come to think of it, could I just leave the PSU mostly intact except for the 33uF cap instead of the 3.3uF (probably will just add a 33uF cap in parallel, easier, and I have no other use for a 3.3uF huge film cap like that), and changing the 100uF cap in the PSU to a 220uF?
The caps values after the choke aren't extremely critical. With unregulated supplies filtered by LC or RC cells, you have a trade-off. It is good to have a final RC filter per channel to reduce crosstalk. But if you put too high a resistor and too low a cap, you actually increase the ripple (because of the varying current draw) compared to the ripple after the choke (it's an easy sim in ltspice if you wanna see it). So put a decent value cap after the choke (100uF is fine) and the biggest cap you can after the 220R resistors going to each amp.
What's the purpose of the 4x15K 0.6W (60K / 3W) resistors?
The 100uF/100V cap is a complete mystery as well...
With an aikido, the top tubes' cathodes are sitting at B+/2. To avoid stressing the tubes, it's best to bias the heaters somewhere around B+/4, so that the cathode to heaters voltages aren't too big. So the 15K resistors are a voltage divider (so you cannot use a single resistor but you could use 47K-15K) tied to the heaters CT (or fake CT with resistors). The 100uF cap in // filters that reference point. Its value isn't critical (voltage rating is).
It was already explained at length by Nikongod at the beginning of the thread.
Edit1: wrt the transformer: I see two 6.3VAC windings, no 5VAC for the rectifier ? Do you have resistors to drop the excess 1.3V ?
Edit2: I'm going to be a bit nasty: you could keep the tube rectifier for the nice look but disconnect it and replace it below the hood by a pair of uf4007. Voila, instant 50V gain.
Edited by 00940 - 2/4/14 at 2:33am