[time-nuts] RB video

Brucekareen at aol.com Brucekareen at aol.com
Fri Aug 9 21:20:54 UTC 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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