|
Hello-
Just a report on an experiment
tried on a Drake TR-3. I restored an early TR-3 that had the "Soup Can" 9.0 Mhz
IF filter pair. The TR-3 was in very nice condition and I plan on actively using
it. I like the higher quality 8 pole filters and had found a LSB / USB pair that
came out of a Harris military transceiver.There were 2.8 Khz. wide, 8 pole, 400
ohm impedance compact PC mount filters.
There will be plenty of room for
this assembly, the only thing that is tight is there is just barely enough
height for the 1-3/4" perf board.
Here is how I installed them in
the TR-3:
1. I removed
the "Soup Can" filter assembly, unsoldered the case, opened case so that I
could unsolder the two pilot lamp switching wires from switch assembly. Note
where these two wires go, they will be re-soldered later.
2. Unsolder
the 3 cond wire going to each filter matching transformer.
3. I used the
existing switch the "Soup Can" filter was built upon. The LSB filter is the
bottom four crystals, top four crystals are USB filter when you have the
assembly laying on bench with shaft towards you and the longer 3-cond cable
to the left, just as it would be in the radio when radio is laying on bench
upside down with front panel toward you.
4. On
the rear switch deck note the switch terminals {they are across drom each other
180 degrees} the red wire in each 3 cond pair is soldered to - this is the
in / out hot connection for the assembly ( I call "red wire terminal"). Unsolder
the red, black and shield (bare) wires of
each 3 cond. cable.
5. On the
rear switch deck note the switch contacts above / below the ones the red
wire were soldered to. (These are the contacts that will be used to wire the new
filters to.) There will be crystals soldered to them. There will be
crystals soldered to the inner switch deck. Unsolder all crystals and
capacitors, but do not disturb switch in any other way.
6. Use a
1-3/4" square piece of perf board with copper PC pads on .1" centers, such as
the Radio Shack #276-148 PC board. Place Harris filters on side of board without
copper pads, the filters terminals will line up and go through perf board.
Place LSB filter on bottom. The two filters will take up nearly all of the perf
board. Note the two ground pins of each filter. I soldered a ground bus
wire across board for each filters ground pin pair.
7. Using
short pieces of bus wire solder one to each filter hot pin (4 total). Bend these
bus wires so that this perf board assembly can be brought up within about 1/2"
of rear switch deck.
8. Solder the
two leads for LSB filter to
the rear switch section contacts : One filter lead goes to switch
contact under the red wire terminal on one side and to same terminal on other
side of switch.
9. Solder the
two leads for USB filter to the rear switch contacts : One filter lead goes
to switch contact above the red wire terminal on one side and to same
terminal on other side of switch.
10.
Install 2 bus wires going from ground bus of LSB filter (one at each end of
filter) PC board to switch frame, solder to frame as Drake did.
11. Repeat
this for the USB filter.
12. Prepare
two lenghts of RG174 ( I used Teflon type) to replace the 3 cond cable
assemblies.
13. Solder
the center cond of each coax to corresponding red wire terminal, coax braid to
switch frame.
14. Install a
100 pF. trimmer from each coax center
conductor to ground at switch assembly. This will be 2 trimmers total, one on
each side of switch.
15. Install
the assembly in radio. Reconnect RG174 coax to filter matching transformers. Do
not use center pin of either transformer, solder braid to the transformer pin
nearest rear panel on each transformer, center cond to pin nearest front
panel.
16. Reconnect
the two pilot lamp switching wires to switch terminals.
16. Double
check your work, then power up radio. Do a quick chech using calib to make sure
each filter is working OK. If so, allow radio to warm up good.
17. Center
the 9.0 Mhz osc between two filters. I spend a little time with this trying to
get pitch of sound as close as possible on each filter. I noticed this filter
pair seemed "closer", in that I could get nearly identical pitch on each
filter.
17. Do the
filter matching alignment and peak the 100 pF.trimmers, repeat this once to make
sure.
I have seen TR-4's from factory with
"Soup Can". I was very pleased with the performance of Harris filters. They are
pretty tight on skirts and with the 2.8 Khz BW sound good. I hope I have
helped here, 73 from a fellow Drake fan. CUL, Byron
WA5THJ.
| 
