Visit(Classified)

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-02820A000100040018-7
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 3
• Document Creation Date: December 9, 2016
• Document Release Date: April 30, 2001
• Sequence Number: 18
• Publication Date: December 16, 1955
• Content Type: MFR

Approved For Release 2001/07/16 : CIA-RDP78-0282OA000100040018-7
16 December 1955
SUBJECT: Visit to 25X1A5a1
25X1 Aga 1. A visit was made by i r and 25X1A9a
RSS Project Engineer, to the plant and office, 7 - 8 25X1A5a1
December 1955, for the purpose of obtaining Information relative to that firms
Model GPT-750 General Purpose Transmitter, It was desired to see and inspect the
production prototype model of this transmitter and to obtain an estimate as to when
this model would go into production.
25X1A5a1
2. The following persons atMwere seen and consulted:
Vice President, Sales
or Engineer
ngineer
3. The complete transmitter set consists of two units, the transmitter unit
and the remote control unit.
25X1A5a1
4, The transmitter unit is enclosed in a steel case approximately 32 in, wide
X 20 in. deep X 42 in, high; the case has a blue-gray crackle finish. The transmitter
unit is made up of three sections, the HF section, the modulator, and the power supply.
Each section has its own main chassis and panel and is drawer mounted on heavy-duty
slides. Captive type bolts are used to secure each section to the case; heavy-duty
handles on the panel of each section and slide stops facilitate removal of each
section from the case, A rear cover plate on which two air filters are mounted
completely encloses the back of the case. With the exception of the high voltage
plate transformer, and a few minor parts, all components of the transmitter are with-
in the three:',drawer mounted sections and are therefore easily accessible for inspection
and maintenance, Interconnections between sections are made by cable and plug assem-
blies. Primary power is brought into the cabinet through a 3-wire twist lock receptacle
in the rear of the cabinet. RF output is taken off from the cabinet through a side
mounted SO-239 type coaxial connector; internally RF is supplied to this connector by
means of large, silver plated contacts on the RF section chassis contacting plated-
brass spring type contacts connected to the coaxial connector mounted in the side of
the transmitter case. The RF section consists of a PMO type master oscillator, a
crystal oscillator, multiplier stages, a buffer-amplifier, and a power-amplifier and
a power-amplifier stage. Provisions are made for connection of external excitation
through a miniature (Amphenol BNC) type connector. The modulator section consists cf
three-stage modulator and the power supply for the first two, driver, stages. The
power supply section contains the high voltage supply for the RF and modulator sections
plus low and medium plate and bias supplies for the RF section, power control switches,
circuit breakers, overload and delay relayq, and fuses.
5. The remote control unit, Model RTC, is enclosed in a steel cabinet approxi-
mately 10 in, high X 15 in. deep X 20 in, wide. This unit includes a speech amplifier
and its power supply. An audio oscillator with three selectable tones is provided;
this oscillator may be used for monitoring a keyed signal and/or as a tone generator
for MCW operation. On the control unit panel are monitor and key jacks, an audio
Approved For Release 2001/07/16: CIA-RA000100040018-7
 Approved For ReIea 2001/07/ 10 20A0004 0040018-7
level meter, a stand-by operate switch, gain and clipping controls.
6. ' Ma j or details of the ^ Model GPT-750 Transmitter: 25X1 A5a 1
Primary Power: 115-230 V., Single phase, 50-60 cycles, approximately 3 Kw.
Frequency Range: 2-30 Mos., in fo}i l bands.
Carrier Output: 750 W. CW or FS, 2-20 Mos.; 500 W. OW or FS, 20-30 Mos.
450 W. A3, 2-20 Moe.; 300 W. A3, 20-30 Mos.
Output Impedance: Unbalanced, 50-1000 ohms,
Frequency Selection: Manua:L
Tuning: All tuning from front panel.
Audio Input: Carbon microphone (Battery must be supplied externally); 600 ohm balanced,
Frequency Control: Master Oscillator; direct reading over range of oscillator.
Crystal: Three crystal positions selectable from panel switch,
RF Section
Modulator Section Power Supply Section
2 - 6AH6
1 - 5R4GY 2 - 5R4GY
1-6BE6
2-6L6 1-6X4
1 - 6BF5
1 - 12AT7 2 - 872A
2-604
2-810 2-OB2
2-12AT7
1-0A3
3 - 12AU7
2 - 4-250A
1 - 6146
1 - OA2
7. Major details of the= Model RTC Remote Control Unit: 25X1A5a1
Primary Power: 115-230 V., Single phase, 50-60 cycles, 50 W.
Input Level: -50 db for full output.
Output Level: 0 Volts up to plus 6 dbm, continuously variable.
MOW Output: Three Tones, selectable (500, 1000, 1500 cps)
Tubes:
1 - 5Y3 2 - ].2AT7 1 - 12AU7 1 - 12AX7
8. Operation of the transmitter and remote control unit was demonstrated and
25
explained by The transmitter output was fed into a dummy load which was
25
loaded up to la
ne kilowatt. Telephone and telegraph (CW and MOW) operation
were checked,
transform Appfove oor 16lease
pointed out that wherever possible similar type tubes,
~ttlfOfAEtsCYi-ft0lil- MOOD 660 64- 'es problems. The
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-3
present design of the transmitter does not permit a keyed carrier during MCW operation,
generator is keyed, therefore prohibiting one-frequency duplex operation.
tated that a small plug-in unit could be constructed which would permit
eying a carrier as well as the modulator. This unit would contain the tone
oscillator and a circuit for simultaneous keying of the carrier and the modulator;
a CW MCW switch would also be incorporated on the unit. Such a unit could be mounted
(plug-in) on the modulator section chassis with minor modification to that chassis.
The stage preceding the power amplifier stage acts as a straight-through amplifier.
By the use of microswitches, in conjunction with the tap switch on the power amplifier
plate inductance, plate voltage is removed from the tap switch before its contacts are
opened during band-switching, and voltage to the switch is applied only after its
contacts have again closed, Construction is rugged since this transmitter was designed
for mobile as well as fixed use. Wiring, cabling, and general construction practices
appear completely satisfactory. The unit inspected lacked tube clamps in one or two
-where
they might be advisable. This was brought to the attention of Mr.
ho said that clamps would be provided at those points if desired. Forced
ction is employed. An intake blower is installed to draw air into the lower
rear of the cabinet; an exhaust blower is located on the RF deck immediately to the
rear and above the power amplifier tubes, In the power supply section above the
chassis, three terminal blocks are mounted in a row; from these blocks,readings can
be taken of the output and input voltages from the bias, low and medium voltage
supplies; all contacts on the plate relay and the power amplifier screen and plate
overload relays are also terminated on these blocks.
9. Although this transmitter is not in pr stated that 25X1 A5a1
action should begin in early January, 1956, also mentioned that 25X1A5a1
will soon construct a building near the pros new building will
Lldle all =receiver and transmitter assembly.
10. Instruction manuals for the GPT-750 Transmitter have not been completed.
Drawings of the transmitter and remote control unit were obtained, however.
25X1A5a1
Approved For Release 2001/ - 78-02820A000100040018-7