PS Capacitor Voltage Rating

[microbus67]

I'm wondering if 400V rated Nichicon LQ series would have enough margin for C8 and 9?

Looks like 333V is coming off the pin of the 6AX5GT, then dropping(a little!) through the choke before arriving @ C8

Anyone running 400V PS caps?

Thanks for any help

[TomMcNally]

Hi and welcome to diytube ...

I have to admit as probably the person who has built more
get*set*go amps than anyone else, I don't recall ever measuring
any voltages, these things just work when you turn them on.
I've always used the Mouser BOM to order parts, and they
are 450 volt rated caps. I would think 400's would be fine.
Often, printed circuit board parts selection is based on parts
that physically fit, temperature rating, as well as electrical
specs.

Give it a try, you should be fine.

[microbus67]

Hi Tom,

Thanks for your kind and helpful reply(and for giving us all so many superb amps to study and emulate : )

I'll go with the Nichicon 220/400V's(with one hand on the variac, watching for the magic smoke). They are beautiful little tanks, and they fit the board so well!
If they detonate, I can always bump the specs...

Your reassurance is comforting though, & I appreciate it.

[EWBrown]

333VDC is about 83% of 400V, which is an almost ideal situation, as electrolytics seem to be at their best when run at approximatley 80% of the rated voltage.

The first and last caps in the PSU string should be 33 to 47 uF, most important is the cap fed by the 6AX5 rectifier, a big cap there will kill the 6AX5 in short order.

400V rating is plenty good for the GSG, with the specified voltages and the 6AX5 rectifier, though I would not use them with a solid state rectifier, because the B+ would briefly surge above 400V until the other tubes are fully warmed up. The slow warm up of the tube rectifier prevents this problem.

I've been using 180 uF / 450 or 180uf / 500V caps which I found at an antique / junk shop in NH a few years ago. I've used these caps in most of my amp bulds for several years, they were perfect for the ST35 boards, and the Ike boards, as well as the GSG. They are also the same dimensions as the specified 120 uF / 450V caps.

I was there with the intention of looking for vacuum tubes, old radios, etc, and the proprieter showed me a big cardboard box full of caps, very useful SS rectifiers, and other goodies that he just had gotten, and he just wanted to unload it fast and cheap, as it didn't fit the normal "profile" of the shop's offerings. I later found that this pieces-parts stuff came from a local solar elecric small business that went TU before it really got off the ground.

Someone else made the "big score" on the leftover solar panels, before I got there

I generally will make extensive voltage and current measurements on the first build of every kind of amp I build, then just go on the presumption that the rest of the same kinds will operate at nearly the same characteristics. That works well, except when I occasionally goof up and put in a wrong value resistror, which can happen for me as I have some degree of color-blindness in the blue/violet part of the spectrum, and those resistors with light blue bodies are especially vexing for me, as the blue, green, violet or gray bands are hard for me to discern. But then that's what DVMs are for...

Then the "five band" resistors can be confusing, is it a 1K, 1% resistor or is it 110 ohms, 1% Depends on which end is the "start"

/ed B

[microbus67]

With 33uF/450V first & last, the 6AX5 should be happy...
Charging current should remain moderate(though I do admit to killing a 6AX5 with a 200uF input cap. It was pungently memorable).
Thanks!

[TomMcNally]

Send some pix when you get your amp done, we'd love to
see how it came out.

... tom