Re: telequipment s54a trace too low on y
But it will still hurt like h**l.toggle quoted messageShow quoted text
Sent from K5JLR
-------- Original message --------
From: Chuck Harris <cfharris@...>
Date: 09/16/2018 8:08 AM (GMT-06:00)
Subject: Re: [TekScopes] telequipment s54a trace too low on y
A rule of thumb that was around during the days when
hams and TV repairmen were often exposed to shocks from
the gear they were working on was it takes more than
1 Joule of energy stored in a capacitor to kill you.
The threshold case was stated as a fully charged 10uf, 450V
J = 1/2 C x V x V
In the case of anode supplies on CRT's, the V is high, on
the order of 12KV, which leads to capacitance needed to
reach one Joule of energy as greater than:
C = 2 J/(V x V) or
C = 2/(12000 x 12000) = 1.39E-8F, or 0.0139uf @ 12KV
Which is about 2500 times the capacitance of a CRT's internal
structure (I measured 6pf for a 2465 CRT), and way more than
the capacitors used in the power supply's voltage multiplier
circuit, which is by design about 0.0005uf total capacitance
at 12KV for a 545 type scope, and similar for a 2465.
The above assumes you are a normal healthy adult, with dry
skin (as opposed to wet), and no weeping wounds at the contact
These values were designed into the circuitry to protect the
accident prone technician.
The point is, you are at nearly zero probability of killing
yourself with the CRT's anode supply. It just doesn't have
the Joules necessary.... it isn't even close.
Far more deadly is the lower voltage supplies found in scopes.
When you go around assessing danger, remember: 10uf @ 450V