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.
