On 4/21/2013 9:05 AM, Michael Black wrote:
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
My admittedly 60 year old memory is that the A had selenium.
At work we replaced them with some special silicon replacements
when those became available. They were the same form factor so
we just had to remove the old ones and put in the new ones. I
wouldn't bet you could still get those, but it wouldn't be a
very big job to put in a terminal strip and use 2n2006, or whatever
is available now.
Bill