Hello-
I have been following this thread on duplicating the Drake TR-4 noise
blanker closely. Actually, I have been thinking of trying to do so myself for
some time, and have been communicating with certain folks regarding such. I was
hoping to find a scrap noise blanker to strip the components from, namely to
unwind the torroids (to get winding info) and then to measure permeability of
the cores.
As far I know there is no difference between the different versions of the
noise blanker for TR-4 series, regarding the PC board itself. I have compared a
later 34-PNB PC board with an early 9-NB PC board and the circuit is the same.
There is some confusion regarding the little PC board that was supplied
with some early 9-NB noise blanker kits. I believe the confusion stems from the
different impedances of the IF filters and their matching transformers. Some
early TR-4's had the soup can IF filter, wheras later ones went to the nice 8
pole units. The soup can has around 2200 ohms resistors across matching
transformer winding versus about 470 ohms for the 8 pole units. The little PC
board was for matching into these, but is really not needed as was later proven
out.
I have seen all the various noise blanker installs, from the early 9-NB one
using the added switch concentric with the PA Tuning control, to wired in
TR-4's with front panel switch to the plug-in 34-PNB. I have removed the noise
blanker (from parts unit TR-4's I bought) from several early-type installs with
the little matching-PC board, then re-installed these in TR-4's but minus the
little PC board. I installed one of these blankers in my TR-3 with good success.
I would like to participate in an effort to duplicate the noise blanker PC
board. The PC board is the main problem to me, as I don't believe there is any
artwork surviving out there. It appears we would need the help of someone who
could produce the artwork, using an existing board as a guide. As far as
getting the parts and construction I believe that could be done OK.
So here is my two cents on the thing.
Thanks, Byron WA5THJ
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