[time-nuts] RB video
Brucekareen at aol.com
Brucekareen at aol.com
Fri Aug 9 17:20:54 EDT 2013
I believe the subject video does a nice job introducing viewers to the
construction and potential of EXTRON's extensive of NTSC video equipment housed
in nice, reusable cabinets. The cabinets that I am familiar with have
slide-in front and back panels of 1/16-inch aluminum that can easily be
replaced. Many units, including distribution amplifiers, have blank front
panels.
The power supplies are sometimes husky, too; apparently being designed for
the largest power demand circuitry EXTRON housed in the cabinet. For
example, the ADA 6 300 MX distribution amplifier has a Signal Flathead power
transformer with dual 8-volt secondaries rated at 24-watts overall. These
windings, in series, connect to a bridge rectifier and 6800 uFd/35-volt
filter cap to deliver about 11.8-volts. There is a 7805 +5-volt regulator and a
LT1054CT switched-capacitor that delivers -12-volts that is fed to a 7905
-5-volt regulator.
As mentioned by others, the 300 MHz distribution amplifier, (6 outputs each
for R, G, & B), are a little marginal in output capability, but I have
found them to work fine for 1, 10, and 100 MHz distribution. I installed one
of David Partridges divider boards in the EXTRON cabinet and managed to
power it and a 10 to 100 MHz multiplier unit, as well as the distribution
amplifiers, from the internal EXTRON power supply. Specs say the distribution
amplifier, alone, consumes 10 watts.
Many of these and similar EXTRON boxes have been obseleted by HDTV and are
found on eBay at low prices.
Research has shown that 50 and 75-ohm BNC connectors have the same outward
dimensions, although some 75-ohm versions might have internal matching by
using thinner internal inner conductors. I don't think it makes a lot of
sense to convert the 75-ohm outputs to 50-ohms as the internal amplifiers
cannot be heavily loaded at high output. There is a little more voltage drop
across the 75-ohm driving resistors, but this is useful in reducing the
load on the amplifiers and provides increased isolation between outputs.
The top, bottom, and sides of the cabinets are formed of 1/8-inch aluminum,
with grooves for the front and rear panels. RF re-users may want to add
bonding conductors to these separate parts, to improve the electrical
shielding.
Finally, circuit boards of the earlier distribution amplifiers I
purchased, have through-hole rather than surface-mount components and are probably
easier to modify.
Bruce
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