Scientific Radio Systems
SR-120
1 Kilowatt Transceiver
 


I pulled a stint working at SRS in Rochester, New York, and came in contact with the SR-120 Transceiver.
I always liked the layout of the unit and thought I would like to get my hands on one for the "Ham Bands".
Well I finally did. The unit I bought came from Greg Carter KX4R, who is now included in my list of Good
Friends, from the Atlanta, Georgia area. The frequency coverage is 1.6 Mhz to 30 Mhz continuous for this
particular transceiver.Gregs' Station and equipment can be seen >here<
The exciter is a "Hybrid" unit consisting of solid state, and tube technology, nicely blended to give a functional
"channelized" unit, with good output power up to 150 watts of SSB or CW or AM operation. It is a ten (10)
channel unit that is crystal controlled. The final output circuit sports three (3) 6146 tubes. I received a "spare"
exciter in the package deal from Greg. The exciter model is SR-210. These exciters were also sold as stand
alone units and worked with the SR-610M antenna remote coupler, which was also channelized and pretuned
for the frequencies setup in the exciter.

The amplifier section is the model SR-110, which brings the actual RF output to the 1 kilowatt level and is a pair of
Eimac 3-500Z triodes in Class "B" grounded grid. Running with 2500 volts DC on the plates, from the high voltage
supply with a one (1) amp current capability. A large fan is included for cooling the 3-500Z tubes and allowing for continuous service.
All of the components in the amplifier are heavy duty for long life and low maintenance requirements. The SR-110
Linear Power Amplifier is designed to amplify the output of an exciter or transceiver with 65-150 Watt output
capability to a level of 1000 Watts peak-envelope or average power, depending on mode of emission. Modes of
operation include usb, lsb, isb, am, cw and fsk, depending on the exciter used.
The SR-110 is basically a programmed unit, with eleven rf bands to cover the 1.6 - 30 Mhz hf range. The programming
system allows internal correlation of up to ten exciter channels with the necessary bandswitch and fine tune setups
required to operate on the exciter frequencies. Each channel is individually tuned to the assigned frequencies during
alignment of the LPA.
The High Voltage supply was fairly easy to check and after cleaning, the components were rewired for 115 VAC
operation. The components are very heavy duty and should withstand usage even on "old buzzard" transmissions.
Here is a collage of the various pieces that go into making the System the SR-120.
Since I "Have No Room", I moved the System upstairs
next to the "Coffee Pot'
for convenience of course!



I mostly had to just clean the units up and change the operating frequencies to get the system into operation.

The crystals were ordered from Peterson Radio, and as I got two (2) exciters I decided to set one up on
CW frequencies and one on the popular AM frequencies, with a few channels set aside for SSB operation on
80 and 40 meters. This would enable me to remove one exciter from the rack and install the other, depending
on what modes I wanted to operate. The CW exciter is actually a CW and RTTY exciter on 80 and 40 meters.
While the AM exciter covers 80 and 40 meters with "ECARS" and a few local frequencies for talking to guys
on 40 meters using SSB.
Exciter number one (1) is crystalled up for the following frequencies:
Channel 1 - 3870 KHZ    Channel 6 - 7248 KHZ
Channel 2 - 3875 KHZ    Channel 7 - 7255 KHZ
Channel 3 - 3880 KHZ    Channel 8 - 7285 KHZ
Channel 4 - 3885 KHZ    Channel 9 - 7290 KHZ
Channel 5 - 3890 KHZ    Channel 10 - 7295 KHZ
Exciter number two (2) is crystalled up for the following frequencies:
Channel 1 - 3545 KHZ    Channel 6 - 7030 KHZ
Channel 2 - 3550 KHZ    Channel 7 - 7035 KHZ
Channel 3 - 3610 KHZ    Channel 8 - 7045 KHZ
Channel 4 - 3615 KHZ    Channel 9 - 7080 KHZ
Channel 5 - 3892 KHZ    Channel 10 - 7085 KHZ
Also in the rack of the SR-120 is a Scientific Radio Systems CW Identifier which is programmable for
callsign and keying speed. The model is the SR-840, and it provides audio output as well as "dry contacts"
for regular CW keying of the exciter.
Also for this system is the Remote and Local control units Model 1650A (Local & Remote), which provides
audio and also allows for channel switching as well. Microphone and key inputs and provisions for RTTY service.


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