Philco Predicta Danish Modern 1st working pictures

[robert1]

Originally Posted by dtvmcdonald

You have to be very careful describing what these so-called "baluns" do.

I've looked at lots of sets with them and while the coils are such that they DO
allow making the usual baluns, they are often wired in strange ways. Very frequently they
do NOT provide a balanced antenna input. Sometimes its it is indeed 300 ohms
nominally balanced, but I've seen 300 ohms with one side grounded, other impedances
(including one with a 100 ohm connection to the tuner and 25 ohms out, and
in one memorable case in an RCA 9-T-249 75 Ohms to ground common mode ...
I.e. the two lines had the same phase!

No wonder so many old TVs had antenna problems.

That is why i mentioned the balun coil in a earlier post. i actually blew out a balun on a late fifties RCA just by merely connecting the CATV cable with a 75 / 300 ohm matching transformer to the antenna leads. the matching transformer was apparently bad because there was a low impedence between the cable sheath & the 300 ohm connectors. that is not supposed to be, but i guess that is what i got for using a cheap matching transformer without checking it first.