Try it, Barry. I'll stand by and laugh. I just got a zap from a Fisher
FM tuner that I routinely have plugged in to an isolation transformer
(together with a variable AC transformer) as I do with all things on my
workbench. Many old tube sets have capacitors from the line cord wiring to
the chassis which can be pretty tickly, especially when these sets did not
include the third chassis grounding wire in the line cord. I accidentally
touched the output side of the Fisher transformer - that would be DOUBLE the
isolation in place. 120 volts AC - or more - will bite you when you touch
it, isolation xfmr or not.
Isolation transformers are good for preventing large currents from flowing
when you short things out which can blow fuses and start fires, but they
don't do anything to reduce the voltage - that's what their purpose is.
Greg
----- Original Message -----
From: "Barry Kasindorf" <[email protected]>
To: "Antique Phonograph List" <[email protected]>
Sent: Friday, February 17, 2012 9:09 AM
Subject: Re: [Phono-L] Does anyone know how to make a Jones Motrola _safe_?
Not true Greg. You would have to touch 2 different places with potential
to get a shock and the case can't have that.
Unless the isolation transformer is bad it makers it safe. That is how you
can use those AC/DC sets with the case hot safely. The isolation
transformer isolates it from ground completely.
On 2/16/2012 10:10 PM, Greg Bogantz wrote:
An isolation transformer would not prevent getting a shock from the
case of the Motrola if it develops internal leakage. Grounding the case
of the unit as described previously is the best plan.
Greg Bogantz
----- Original Message ----- From: "Philip Carli"
<[email protected]>
To: "Antique Phonograph List" <[email protected]>
Sent: Thursday, February 16, 2012 8:45 PM
Subject: Re: [Phono-L] Does anyone know how to make a Jones Motrola
_safe_?
Many thanks! Another suggestion I've had is the use of an isolation
transformer at the plug - any thoughts on that? PC
________________________________________
From: [email protected] [[email protected]] on
behalf of Greg Bogantz [[email protected]]
Sent: Thursday, February 16, 2012 8:27 PM
To: Antique Phonograph List
Subject: Re: [Phono-L] Does anyone know how to make a Jones Motrola
_safe_?
I believe the Motrola has a metal case. The danger can occur if
there
is electrical leakage from the internal wiring to the case and its
attached
metal parts which can occur due to carbonized insulation that can begin
to
develop a lower resistance. I would recommend first testing with an
ohmmeter to determine if there is already leakage from either of the
wires
leading from the motor to the case. An ohmmeter reading should indicate
a
very high or infinite resistance from either wire to the case when
things
are correct. If you measure any significantly lower resistance, the
internal wiring will need to be redone or repaired. If there is good
isolation from the motor wires to the case, I would recommend replacing
the
line cord with a modern three-wire cord with a 3-terminal AC plug.
Connect
the black and white wires to the motor circuit as was done in the
original
2-wire cord. Then connect the green wire to a screw on the metal case.
This will privide a grounding connection from the case to your household
earthing system. If electrical leakage should develop in the future, it
will be routed thru the green wire to your household ground system
(assuming
you plug the cord into a modern 3-wire outlet). In the worst case, it
will
blow a fuse or circuit breaker rather than leaving the system a shock
hazard.
Greg Bogantz
----- Original Message -----
From: "Philip Carli" <[email protected]>
To: "Antique Phonograph List" <[email protected]>
Sent: Thursday, February 16, 2012 7:08 PM
Subject: [Phono-L] Does anyone know how to make a Jones Motrola _safe_?
I have a Jones Motrola I'm trying to rewire, but I read that they can
be
dangerous in their original ungrounded state? Any ideas on how I can
deal
with this? Any help would be appreciated. Thanks, Philip Carli
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-Barry
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