[Peter Wieck]

On Nov 6, 2:14 am, "West" wrote:
"Peter Wieck" wrote in message

ps.com...





On Nov 5, 8:40 pm, "West" wrote:
No one suggested using a scope except for illustration. You are somewhat
clever in trying desperately to dig for insignificant and irrelevant
issues
that you can exploit for your agenda. Measuring a DC power supply with a
DVM
in the AC mode is standard procedure for a service tech to quickly
observe
ac ripple on the power supply.

YIKES - please explain to the assembled multitude how AC will pass a
bridge rectifier such as to be measurable on an AC meter even with no
filtration at all. Chopped DC ain't nohow AC.

Peter Wieck
Wyncote, PA

Don't you understand? I'll try again.
If there is ac on the dc rail because of leaky filter cap, bad diode, etc.,
it can be roughly measured with a dvm on the ac mode. If you have a bank of
various dc supplies as in a system network or any commercial equipment you
can easily go down the line with your dvm measuring the various dc levels
and switching over to ac on your meter to measure an ac component, if
present. This will give you the level of dc and if ripple is present, the ac
level. Naturally all these simple test can be performed with a scope, switch
on the input to DC, then AC. I don't know how many times and ways I can
explain it to you. Perhaps someone else can do a better job but this is how
I taught it to my field engineering students for several years with no
problem. I believe you owe me and the OP a heartfelt apology. We will not
hold our breath, of course because I do not think Peter the Great has such
capabilities

west

PS I bottomed posted this time because your question had no insults and may
actually be a legit question.- Hide quoted text -

- Show quoted text -

West:

Please answer the question as-posed: How does an AC meter measure
across a bridge rectifier? Even if no filtration at all? Hint: Before
I posted back to you, I tried it on the bench last night. Results:

Single diode, 120V in, 84VDC out, ~4.3V of AC ripple (half-wave)
Dual Diode, 120V in, 84VDC out, ~2V of AC rippple
Bridge, 120V in, 169VDC out, 100mv of AC ripple.

No caps involved, Fluke "True RMS" DVM

Try it yourself. We are discussing Vacuum Tube equipment with solid-
state rectifiers at (relatively) high voltage. Not Solid-State
equipment typically operating at a B+ of 80V or less, and where half-
wave rectifiers might be common.

HINT: When bridge diodes fail in this situation, the B+ drops big-
time. The amp goes silent.

Just for round figures, half-wave rectifier = Vin x 0.7
Bridge Rectifier = Vin x 1.4

Point: I do not take money to service anything. This is a hobby. Nor
do I typically take items to service without the owner being present
(to learn what I did) unless I am dealing with someone who is elderly,
too young, or otherwise unable (or unwise).

Peter Wieck
Wyncote, PA