On Sun, 21 Apr 2013, Phil Allison wrote:


"Trevor Wilson"

** Here is a pretty good pic of the insides of a 545B.

http://www.barrytech.com/tektronix/v...k545bright.jpg

The AC tranny looks like it *might* be 500VA - but I expect Tek would
use a
conservatively rated unit with a low temp rise.

If the OP would care to measure the primary resistance - I can say for
sure.

**I found my 545A manual.

Power consumption is rated at 500 Watts. Weight is 65 pounds.

Fuse ratings:

6.25 Amp Slo-blo 3AG for 117VAC 50Hz
6 Amp fast blo 3AG for 117VAC 60Hz
3 Amp fast blo 3AG for 234VAC 60Hz
3 Amp slo-blo 3AG for 234VAC 50Hz


** Hmmmmm.....

Those numbers make me think the AC tranny is quite conservatively rated for
voltage and frequency.

Doing so, reduces the severity of inrush surges quite a bit.

BTW 1:

If you operate a 240V rated tranny on 120V - there is barely ANY inrush
surge at all.

( Electro caps in the PSU not withstanding. )

BTW 2:

The main source of inrush surge with tube gear is often due to all the tube
heaters being cold at switch on - particularly if the rectifiers are
vacuum tubes. The buggers take quite a time to warm up and increase in
resistance too.

Which reminds me, there's a time delay in there. I don't see it on the
schematic (which is spread over many pages so I'm not sure which section
it's in), but I suddenly remember there's a point when it starts up when
things suddenly kick into operation. I seem to recall hearing the relay
kick in. Since I can't find that on the schematic, I'm not sure what it's
controlling.

But the 545B uses selenium diodes - right?

I have the B manual and they are listed as silicon. I think I would have
noticed selenium when I was inside the scope if they'd had them.

Michael