RadioBanter - View Single Post - I was way way stoopid

October 26th 05, 05:12 PM

wrote:
Yea Chuck,

What I did was to regard a penciled in voltage on a schematic as real.
Previous owner penciled in 600v on the plate supply. So ok I figured
I'd stick a 450v cap in each of the two hollowed out cans and I'm good
for near 900v with a pair of sharing resistors. About the time I get
the caps all epoxyed in I take a look at the new Peter Dahl plate
transformer schematic and it says 700v on the plate windings. Sure
enough 700vrms is about 1kv, so my two free 450v caps aint gonna hack
it. I got some free 30mmx30mm 220uf 400v cans. I'll get two of em
into each can this weekend and I'll be ok.

Into the transmitter for about 500 bucks now and it's worth about 200
working. Needless to say I don't want to burn out the new transformer
with a botched recap job.

73
Bob

Hi Bob,

That hurts!

The two series connected 450WV caps would be ok with a no load voltage of
980V. It was a pretty common practice to let things like that happen back
in the day. The capacitors will respond to the excess voltage by building
a little more oxide layer... assuming that they are in good shape to begin
with.

But you will be safer going to the higher rated caps. If you are going
to stick two 400V caps in the same can, be warned that the plastic sleeve
on the 400V caps isn't good for 400V. Use some better insulation. I got
a serious arm-to-arm shock trusting some capacitor insulation when I
foolishly clamped a cap to a floating chassis. I learned a couple of
important lessons that day!

-Chuck