Re: Amp voltage testing question

On Wed, 26 Jul 2006 02:41:32 GMT, Doggone <Running@xxxxxxxxxxx> wrote:

Dave Curtis <dbaudiotechNOSPAM@xxxxxxxxxxxx> wrote in
news:ao0dc293k7rmsj7s7bb9bsdbd5im7qtl1t@xxxxxxx:

On Tue, 25 Jul 2006 15:25:13 -0500, Dave Moore typed:


<jpasono@xxxxxxxxxxx> wrote in message
news:og7cc2lhljqmvb8is5i7b6pkftcsd4mpa4@xxxxxxxxxx
: On a amp / transformer test ,using my Fluke, are the secondary
: transformer leads tested from lead to lead or lead to ground (B+,
: filaments, center tap)? And everything past the rectifier is a DC to
: ground test right? Just trying to get this straight in my head.TIA


If the secondary is grounded ( usually they are in an amp with
negative feedback) then a continuity test (reading resistance)
from the speaker out jack to ground is a valid test,
though it won't tell you as much as an inductance
measurement will.

I thought he was asking about the PT, in which case: yes, both across
the secondary leads and from each lead to the center tap (AC).

Regarding question #2, yes, if it's DC voltage you're checking,
most often voltages depicted in schematics are with respect
to grond unless otherwise indicated.





Before you check across the PT's HV secondary, take a moment to
ensure you meter can handle the voltage. Some amps will have
upward 1000V peak across the secondary. Most modern meters will
fiz out at 600V.

Also consider your test leads. If you're using the original Fluke
leads, you should be OK. Beware of some of the older (vintage?)
test leads. Some have set screws on the side (whoever invented those
should be shot). Any test leads that are dry, cracked or frayed
should be tossed.

To be on the safe side, when measuring PT HV secondaries, clip on
leads fitted with aligator clips, power on the unit, take the
reading and power it off. It's a HANDS OFF method.

One mistake there can mean instant death. Check your life insurance
policy.
Thanks for the safety warning. I was afraid of that so I bought a new
Fluke 189 kit. It is good to 1000 volts if I remember correctly. Just
seems that these books I buy (like Weber's Essential ) and references
to checking never make it plain if they are hooking a negative lead
with an alligator clip to the chassis and then measuring or measuring
across the coils on a transformer.
.

Relevant Pages

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