This was my FM-DX machine from late 1973 thru Oct 1979. It was originally
gotten in Apr 1973 for $75 from N5TX across town.
At a smoke test there one of the screen grid resistors did just that (a
shorted wax-paper bypass capacitor). It came with a Sam's PhotoFact and
the "loan" of a vintage Precision E-200-C signal generator for alignment
assistance. Schematics and other descriptive material is widely available
on the Web so I wont add much here in that regard. Mine came without a
cabinet so it was mounted on a piece of particle board - making a hefty
item to move about.
Almost a complete retubing and replacement of all accessible wax-paper
capacitors followed. The unit had at one time had a power supply fire as
evidenced by the scorched chassis and wires under the 5U4GB rectifier
The first astounding thing on FM noted was the ability for it to get 97.5
Beaumont next to our 97.3 local. Later that summer Glenn Hauser paid a
visit with one of the Bob Cooper interdigital preamps for FM that was put
ahead of it. That convinced me of its future, so some ICM preamps were
ordered and built (for 88-105, 105-108) with some tuned LC circuitry ahead
of them to minimize overload.
I eventually rigged it for direct audio feed to my reel-to-reel tape
recorder (so much better than acoustic feed!) Restringing the dial (two
cords) was a chore too often repeated. I used this unit for 30-50 MHz as
well (even after I was loaned an SP-600 in Sep 1975) so it did get a good
The tiny dial space for 88-108 MHz (the upper portion of 54-108) made for
some challenging frequency determination (and often redos of the masking
tape scale that I used on there).
One could easily twiddle with the i.f. cans, etc. Doing so I once managed
to be able to tune for silence between 93.7 Austin and 93.9 Corpus
Christi. Of course, with such a narrow bandpass the audio was terrible!
With 200+ VDC on the plates and screens of the VTs one had to be VERY
careful of any attempted mods (like an s-meter, never done). I did
construct an SCA unit for use with it, but other than hearing EL there on
a local rocker, it wasn't pursued. Also, a Wobulator was once shunted
across the oscillator section of the main-tuning variable capacitor to try
to simulate a panadaptor/spectrum analyzer. I managed to see two large
blips of 92.9 on a 3" oscilloscope as it swung by it to and fro.
It was replaced by the TM-1001 in late 1979 and then rarely powered up -
and on the last occasion the sounds of a frying choke in the power supply
quickly put an end to that!
Page Created: Jun 16, 2011