LTT-4 Transmitter (Longwave Telegraph Transmitter)

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Frequency range: 260 to 520 KHz
Modes: CW and MCW
Power output: 150 watts CW, 110 watts MCW
MCW sidetones: 500, 700 or 1,000 Hz
Frequency control: 3 preset frequencies controlled by master oscillator.
Nameplate Data:
    Primary power 115 VAC , 6 amps, 60 Hz.
    Marconi designator: LTT-4  #84010A
    Spec: 81390
Transmitter Dimensions: 24" W x 20" D X 44" H
Transmitter weight: 360 pounds
Power Unit Dimensions: 21" X 11.5" x 14"
Power unit weight: 84 pounds
Circa:  Believed to be 1939.
Comment: Except for the external power unit, the LTT-4 appears to be nearly identical to the LTT-1.

The LTT-4 operates on three preselected frequencies in the range of 260 to 520 KHz (1150 to 580 metres) by means of single bandchange switch.  A keying relay provides "break in" operation up to 45 wpm. The transmitter itself comprises of a self-controlled master oscillator stage (#10 triode tube) driving a neutralized push-pull RF stage which employs #211 tubes. An additional stage using a #10 tube provides tone generator functionality for MCW mode. Radio operator Wally MacLeod says that the LTT-4's  Medium Frequency CW signal had a lot of "drift" to it.

On account of its bulk, the copper oxide rectifier (right) for the high voltage is mounted in a separate case and hardwired to the transmitter.  The bandswitch is in the very centre of the unit.

Note the #211 tubes on the first deck towards the left side. The #10 triode tubes are in close vicinity.

Copper-oxide, power rectifier unit with cover off. The power unit comprises of thirty two sections, wired in full wave rectifier fashion, which provide 1000 volts at 500 ma.

All photos in this table courtesy Laval Desbiens via SPECTRALUMNI

The LTT-4 employed a pair of 211 tubes in the RF output stage. This type is also known as type VT-4C. (E-bay photo)	10 triode. (Courtesy Tube Depot)

Type 211 characteristics: Transmitting triode. Filament draws 3.4 amps at 9-10 volts. Types "A", "B" and "C" designate filament current. Type "D" has a constant voltage filament (10 volts at 3.25 amps). An "E" type  is a "D" type with parasitic-supressor chokes built into the grid and plate leads.

Type 10 characteristics: Power triode. FIlament power 7.5 volts @ 1.25 amps. Plate voltage 425 V max @18 ma. Power output 1.6 watts.

It is confirmed that the LTT-4 saw service aboard the now historic ships CCS Acadia and RCMP St. Roch. Not confirmed at this time but four pre-WWII minesweepers had LTT-4 transmitters  mated with National HRO receivers.

Ernie Falvey, VE1HA, operating Camperdown Radio VCS September 1949. At the left is the Marconi TM-11. The transmitter in the corner behind Ernie's left shoulder is the LTT-4. (Photo via Spud Roscoe)

The tall unit at the left is the Canadian Marconi 200PT transmitter. . To its right is the LTT-4. Both of these were fitted to the  RCMP St. Roch in Vancouver. (Image courtesy Vancouver Maritime Museum)

The LTT-4 has two meters.. One of them is permanently wired into the circuit. while the other is terminated on a plug  (missing) which can be moved to four different points in the circuit depending on what is to be monitored,  This is confusing because the placard identifies four circuit points  but tthe panel only has three jacks. Note that there are no markings above the controls or the jacks. It is believed that his LTT-4 example may have been repainted. (Photo by John Gilbert)

 

LTT-4 Operator's Manual - PDF  ( Provided by Laval Desbiens via Spectral Alumni) This is how the LTT-4 schematic looks when the tiled pages 16 to 23 of the manual are ssembled.  During the original scan of the manual, some parts were missed. These are noted as follows: 1) At the top left, part of the schematic is missing as well as the bootom right.. That's relatively minor.  2) There are two sheets on the right side of the main schematic which are currently orphaned. These likely belong belong with the copper oxide version of the power supply. 3) Ar the top left, of the schematic,  there  is a meter wired to a test cord and terminated with a plug.  It was likely  used to check other parts of the LTT-4 circuit. This test cord is not evident on  the LTT-4 front view photo  which shows  two meters but no test cord.  Both  meters appeared to be are hardwired. Perhaps this is a variant of the LTT-4. It is believed that the original manual is with Library and Archives Canada. If anyone is going there to do any research, can you see if the missing pieces of the schematic can be photocopied? Contact: jerry.proc@sympatico.ca

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Contributors and Credits:

1) Spud Roscoe <spudroscoe(at)eastlink.ca>
2) Vancouver Maritime Museum Curator   <collections(at)vancouvermaritimemuseum.com>
3) SPECTRALUMNI http://www.SPECTRALUMNI.ca
4) Laval Desbiens <desbienslaval(at)gmail.com>
5) 10 triode photo courtesy Tube Depot.  http://www.tubedepot.com/nos-10.html
6) Wally MacLeod <w.macleod(at)ns.sympatico.ca>
 
 

Jun 28/19