5F2A power filter caps?

[ncusack]

Im just wondering if there would be any difference or possible downside to using larger caps in a 5F2A? For example using a 33uF cap for the first 2 16uF caps and using say 16uF or 22uF in place of the 8uF caps? Aside from those changes the power section should be pretty much stock. 325-0-325 PT with a NOS 5Y3.

[MWJB]

Going larger on the 2x16uf main filter caps is a good idea, yes 2x33uf caps will work great.

Going larger on the screen & preamp caps? 16 or 22 will "work" on either/both positions, in fact why not stickanother 33 uf at the screen supply. 8 or 10 won't change the tone at the preamp, 16 or 22 might sound somewhat tighter than stock, you may not care though? Don't go bigger than 22uf at the preamp cap.

Whilst were talking about the electrolytics, don't use a 25v cap at 6V6 pin 8, use 50 or 100v, a larger value than 25uf will tighten up response/reduce sag, you might want to compare to a 100uf cap & see what you prefer?

[ncusack]

Ok that sounds good though I was only suggesting using a single 33uF in place of the 2 16uF for the first stage. Wouldn't 2 x 33uF for the first section be a little harsh on a 5y3? I know you can push it and its something like 22uf suggested for long life with a 5y3 but wouldn't 66uf like you suggest be harmful?

[MWJB]

33uf total will work OK, 66uf won't hurt anything. I wouldn't suggest it if it did.

[ncusack]

Ok that sounds good. Only reason I mention it is because im trying to conserve space on the board maybe ill try a 47uF to start and adjust from there. And thanks for the warning about the preamp cap value.

[Bruce / Mission Amps]

If you are worried about stressing the 5Y3GT, then solder a 47 ohm 2 watt resistor on lug 8 of the rectifier tube socket before connecting your B+ feeder wire to anywhere.
Then you can pretty much run what ever main filter cap uF value you want.

[ThermionicScott]

Just as another data point, I went in the opposite direction when building my 5F2A. I used 20uF-8uF-8uF with the stock 10K and 22K resistors, and the only time I had objectionable hum was when the speaker ground didn't make a good connection to the chassis. There is a little bit of background hum that you can "detect" when you're in the same room, and *hear* if you put your ear right up to the speaker. Alligator-clipping an additional 10-20uF onto the first power supply cap reduced this hum, but didn't have an effect when I tried it on the other two caps.

Really, the only time I have a hum problem is when I plug in a guitar!

- Scott

[tubeswell]

My first build was a 5F2A and I used 2 x 20uF in parallel on the reservoir cap with the 5Y3G and it was pretty quiet. This is a geetar amp - the 5Y3G won't mind 40uF. If you're worried about it you can put (chunky 50-100R) limiting resistors on either side of the HT winding (like Bruce said), and/or you can put a 1N4007 in series with each side of the HT winding to prevent AC being dumped onto the filter caps in the event of a rectifier tube failure (I put the diodes on all my tube rectifier amp builds anyway)