INTRODUCTION
The T-195/GRC-19 is a 100 watt AM transmitter designed and built by Collins in the USA. It is designed to be auto tuning in use, and have the minimum of operator controls. It is part of the GRC-19 radio set, which includes the R-392/URR receiver. The transmitter has 8 preset channels, and will tune them automatically. It will also tune the aerial, whether it is a whip or a long wire aerial. It covers the frequency range from 1.5 to 20 MHz, and may be fixed or mobile. It requires 28.5 volts DC and a current of 25 to 42 Amps, depending on various configurations. The power supply is usually the vehicle battery, but this can be supplemented by an external generator, or a mains type power supply. The transmitter is capable of CW, AM, and FSK at 100 watts. The transmitter is in a sealed aluminium case, which is 11.5 inches high, 14.125 inches deep, 22 inches wide, and weighs 122 pounds. It can be operated locally, or remotely with the C-822/GRC-19 and also as a relay transmitter. The mounting for the transmitter and receiver is MT-851/GRC-19. It uses the KY-116 key, M-29/U microphone, CW-49507 headphones or LS-166/U loudspeaker. The transmitter can use FSK with the addition of MD-203/GR Exciter and Modulator. It is suitable for Arctic, Tropical or Desert climates. The manual TM 11-806 June 1956 covers the first transmitter version, which used rotary dynamotors, but the solid state dynamotors are only covered in later issues of the manual.

The transmitter contains 21 valves. There are 9 valves in the RF section of the transmitter, including the frequency multiplier stages. There are 6 valves in the push pull modulator. There are 6 valves in the 3 servo amplifiers. The transmitter contains 10 motors. There are 2 air blowers, and 2 dynamotors. There are 3 DC motors, 3 AC servo motors. There are also 2 choppers producing 400 Hz for the servo amplifiers.

T-195 Front

This example has been refurbished by PIRMASENS ARMY DEPO. It includes solid state dynamotors, and some front panel repainting. It had plenty of faults, so it may have been a donor for other transmitters, and so it possibly has received many faulty modules.

HISTORY
Collins answered an RFQ (Request For Quote) in mid 1950, by assembling a team of engineers at Cedar Rapids Iowa. They designed and built the T-195 transmitter for portable or jeep use. The T-195 and the R-392 receiver (GRC-19) were used in the Korean war. This radio replaced the SCR-506, or the SCR-299 from WW2. Collins built 4000, Stromberg Carlson built 4000, and Stewart Warner built 6000 transmitters. The program was finished in 1996. Part of the testing was a 20 foot free fall, which was performed by dropping a unit from the roof of a one story building. They were often fitted to jeeps and air dropped.

DESIGN
The transmitter uses a PTO (Permiability Tuned Oscillator) as the oscillator. This is a standard component for Collins equipment, and comes in many frequency ranges, but all covering only a small range. It has an axial shaft that moves a ferrite slug through a coil. The slug, coil, capacitors and correction components, are adjusted at the factory to provide a linear frequency change for the rotation of the shaft. The manual warns the user, never to open or adjust the oscillator. It has a 5749/6BA6W valve as the oscillator and a 5749/6BA6W as a buffer output valve. This PTO is in the normal Collins round can and covers 1.5 to 3.0 Mhz. There is a regulator valve type OA2 to provide a stable 150 volts for the Hartley oscillator. There is -45 volts used to key the buffer to cut-off, but the oscillator keeps running. There is a heater for the PTO but this only operates when the temperture falls below 0 degrees centigrade. All transmitter frequencies (from 1.5 Mhz to 20 Mhz) are generated from this PTO. When the transmitter is set to the MANUAL position, the TUNING CONTROL knob can be unlocked, and the PTO frequency can be adjusted. Normally, one of the 7 channels is selected, and the motor turns the PTO to the correct frequency.

T-195 Top View (L to R: antenna inductor, antenna capacitor, multiplier rack, PTO)

T-195 Bottom ViewView (L to R: modulator, HV dynamotor, servo amplifier, PA amplifier)

The PTO output appears on the front panel with an in and out connector (Type BNC), so that an external RTTY (Radio Teletype) unit can be connected. This is labeled MO OUT and FSK IN.

T-195 PTO

The output from the PTO is coupled to the mutilplier module. There are 4 bands. The multiplier module has several doublers, that produce the final transmitter frequency.
Band A 1.5 - 3.0 MHz
Band B 3.0 - 6.0 MHz
Band C 6.0-12.0 MHz
Band D 12.0-20.0 MHz

This uses a 6AU6W valve, as a doubler, for the last 3 bands. It is merely used as a buffer for the first band (band A). The driver is a 5763 with a tuned 1.5 to 3MHz resonant circuit.

For band B, the same 2 valves are used, but a 3 to 6 MHz tuned circuit is used after the doubler, and after the driver.

For band C, the same 2 valves are used, and an additional doubler is used, a type 6AK6. A 6 to 12 MHz tuned circuit is used after the second doubler, and after the driver.

For band D, the same 3 valves are used, and another additional doubler is used, another 6AK6. A tuned circuit 12 to 20 MHz is used after the third doubler, and after the driver.

T-195 Multiplier Module

The tuned circuits in this multiplier, consist of 10 tuned circuits, with slug tuning, all mounted on a rack, similar to the R390 receiver tuning method. The slugs are mounted on a rack, and this is motor driven, up and down, to tune the multiplier frequency. Each doubler has 2 tuned circuits, joined as a pair. The driver has only 1 tuned circuit, but there are 4, one for each band. The driver also has -45 volts bias, used to cutoff the valve when keying is used. The screen of the driver has different resistors switched in, so that the output is similar for each band. The driver is also neutralized on the top 3 bands.

T-195 Multiplier Block Diagram

There is a frequency window on the right hand side. It has 4 digital VEEDAR ROOT type of rotary mechanical counter. As the bands change, shutters cover the bands not in use, and the digital counters display the transmit frequency.

The output from the driver is capacitor coupled to the Power Amplifier (PA) valve, a large copper anode type 4C150D, which is running in Class C. This has a 28 volt filament and 1000 volts on the anode. There is a meter on the front panel, to display the grid drive, and the anode current. The meter can also be switched to display the battery voltage.

There is a clamp valve (type 5763) which is used to control the screen voltage and thus the anode current. The anode current is reduced during keying. It is also reduced when the anode tuned circuits are switched during band changing.

The PA amplifier can be used as a CW transmitter, or as FSK for RTTY, or as an AM transmitter. There is a large audio amplifier, which uses two 4X150D valves as the modulator.

The audio input is normally from a type M-29/U microphone, or from the 600 ohm line input. This is connected to a preamplifier (12AT7), and then limited (clipped) by a 6AL5W valve. There is a 300 Hz high pass filter followed by a 3500 Hz low pass filter to limit the audio frequency response. There is also some RF filtering on the audio input.

The audio is further amplified by a 12AT7 and a 5814, then connected to the grid of a 4X150D. The audio is also connected to a 5814 phase inverter and connected to a second 4X150D which acts in push-pull with a modulation transformer to develop the audio for AM modulation. There is a VU meter to show the amount of audio applied. In the preamplifier, a side tone is picked off for application to the headset. Also here, a 400 Hz signal is injected when keying is occurring. There is an air blower for the two 4X150D valves.

T-195 Modulator Block Diagram

T-195 Modulator Module

The PA module has an air blower for the 4X150D valve. The PA tuning has 10 bands, switched in by the band change knob. These use taps on the tank coil, 2 variable capacitors, and various fixed capacitors. There is a window to show which band is in use. The bands are:
1.5 - 1.7 Mhz
1.7 - 2.0 Mhz
2.0 - 2.4 Mhz
2.4 - 3.0 Mhz
3.0 - 4.0 Mhz
4.0 - 6.0 Mhz
6.0 - 9.0 Mhz
9.0 - 12.0 Mhz
12.0 - 16.0 Mhz
16.0 - 20.0 Mhz

T-195 PA Module

T-195 Module position

There is a servo system to tune the tank circuit. The grid signal and a signal from the anode inductor, is compared in a discriminator. The phase difference produces an error signal. This system uses a 400Hz chopper module, which is similar to a mechanical vibrator. The error signal is converted by the chopper into a 400Hz AC signal. The height of the signal is the error voltage. The error signal is amplified by a dual triode type 5751, and then by a pentode type 6AQ5W. The amplified error signal is applied to a 400Hz servo motor. The servo motor also has a 400Hz signal at 115 volts AC on its other winding (from the low voltage dynamotor). This will cause the motor to rotate, either in one direction or the other depending on the phase difference (leading or lagging phase). This is the phase relationship between the RF anode and grid voltages, not the 400Hz frequency. The amplitude determines the speed of rotation, the polarity the direction of rotation. When the phase difference is in balance, the error amplitude becomes zero, and the motor stops. The discriminator will therefore adjust the anode capacitor to resonance.

T-195 Output Block Diagram

The output from the PA tank circuit then goes to the antenna matching network. This unit has a variable inductor, and variable capacitors, controlled by 2 servo amplifiers. This will attempt to match an antenna of 73 ohms impedance, over the frequency range of 1.5 to 20 Mhz. The network consists of 4 removable modules, and 1 fixed chassis mounted switch.

T-195 Discriminator Module

T-195 Discriminator Location

The discriminator is a module that produces 2 error signals, one for antenna loading and one for antenna phasing.

T-195 Antenna Matching Network Block Diagram

The 2 signals from the discriminator go to the Servo Amplifier Module. This has 2 amplifiers and 1 chopper in the module. Both amplifiers are similar to the PA servo amplifier. Each amplifier has a 5751 dual triode amplifier, driving a 6AQ5w pentode. Each pentode drives a 400Hz servo motor.

T-195 Dual Servo Amplifier

The Loading servo amplifier drives the variable rotary inductor. This inductor consists of 2 round drums, one is ceramic and an insulator. The other is a metal drum and conductive. When the silver tape is wound on to the conductive drum, it effectively removes turns from the inductor. When the silver ribbon is wound on to the ceramic drum, it effectively adds turns to the inductor. There are limit switches to prevent the tape being wound off at each end. There are 2 motors, a 400Hz servo motor and a DC motor. The DC motor moves the drums quickly to a predetermined position, depending on the antenna and frequency. The servo motor then does the fine tune, being controlled by the discriminator.

T-195 Inductor Module

The Phasing servo amplifier drives the variable capacitors. This module consists of several fixed capacitors, which are connected by a sliding switch. There are 2 variable capacitors as well. These are all driven by a 400 Hz servo motor. The switch moves to the bottom position, detected by an OFF contact. Then the servo motor drives the switch to connect the fixed capacitors, and rotates the variable capacitors, as determined by the discriminator.

T-195 Capacitor Module

T-195 Module position

The final part is the antenna output capacitor. There are several fixed capacitors connected by a rotary switch, and driven by a DC motor. At the low frequency range, the capacitors are connected in parallel with the antenna. In the middle frequency range, the capacitors are connected in series with the antenna. In the high frequency range, the capacitors are connected in series parallel with the antenna. This decreases the tuning range that the matching network must cover.

T-195 Output Capacitor Switch

T-195 Output Capacitors

TUNING SEQUENCE
When the CHANNEL switch is moved to another channel, a sequence of 3 events occurs. These are HOMING, TUNING, and MATCHING (in that chronological order).

When HOMING, the main DC motor drives all RF tuning devices to a start or Home position. The PTO is un-wound to the 1.5 Mhz position. The slug rack is positioned to the 1.5 Mhz position. The band selector is set to the 1.5-1.7 Mhz band. This is very interesting to watch. The TUNING CONTROL knob performs multiple revolutions. The FREQUNECY INDICATOR display, counts down and changes its shuttered windows. The BAND SELECTOR knob rotates. The BAND CHANNEL INDICATOR display shows a rotating disc, changing down the bands. When these are all complete, the next sequence occurs.

When the TUNING starts, the motor reverses, which is the opposite direction to HOMING direction. The PTO is wound to the preset position. The slug rack is positioned to the preset position. The band selector is set to the preset band. This is also interesting to watch. The knobs and the displays move up in frequency to the preset frequency and preset band. The PA servo capacitor rotates to resonance. When the channel frequency is reached, the sequence stops.

To complete the tuning, the last sequence must be performed. This is achieved by holding the TEST KEY switch to the ON position. The MATCHING output capacitor motor spins the switch to select the appropriate capacitor. The INDUCTOR begins winding quickly to the approximate preset point. The CAPACITOR is adjusted quickly to the approximate position. The servos then take over, and the inductor winds slowly to the correct loading point. The capacitor rotates and the fixed capacitors are switched in or out till the correct phasing is achieved.

When the antenna is correctly matched the RED light (TUNING INDICATOR) comes ON. This is for AM operation. FSK and CW operation are slightly different.

CONTROLS
At the top left hand side are the SPARE fuses, the DYNAMOTOR fuses (under a cover), the 24 VOLT fuse, and the TUNING INDICATOR light. Also here are 2 small covers for the modulator air blower. These can be reversed to seal the cabinet, when the transmitter is off. Below this is the large TEST key which can also be used as a PTT switch. There is also a small switch to control the dial light brilliance, or to switch the tuning indicator to a temperature alarm.

There is a large ceramic insulated terminal, which can be used for connecting a whip. It may generate high voltages when in use. There is a Type N connector which can be connected to COAX for a cable run to the antenna. A lever can be moved to allow access to this connector, and it disconnects the ceramic terminal. Below this is a function switch to select RELAY or NORMAL or DUPLEX. Below and to the left is a LINE level control to adjust the audio input, which can be seen on the AUDIO level meter. Directly below the ceramic insulator is the TEST meter switch, which shows PA GRID drive, and PA CATH (the current) and the battery voltage (BATT). The TEST METER has bands on the scale to indicate the usable levels.

In the center of the front panel, is the CHANNELS switch which selects 7 preset channels and one Manual channel. The TEST meter, BAND indicator and BAND knob are here also. Below this is the SERVICE SELECTOR knob, which is the ON/OFF switch, VOICE/FSK or CW selector. It can also select STAND BY, CALIBRATE and REMOTE.

At the right hand side is the Frequency INDICATOR, audio METER, and TUNING control. There is a BNC connector for the companion R392 receiver antenna connection. There is a DIAL ZERO corrector knob under this. There is a reversible AIR intake/exhaust port for the PA air blower. This can be reversed to seal the cabinet, when the transmitter is off.

At the bottom right hand side are the connectors. At the left is the AUDIO input connector. Then the 24 volts input DC connector. Then there are 2 BNC connectors for the oscillator out and the FSK in. then there is the REMOTE control connector, then an EARTH terminal. At the lower right is a DC and muting connector for the R392 receiver.

T-195 Controls

MECHANICAL
The transmitter has a cast alloy front panel, with 1/4 inch thick chassis plates behind it. There is an air blower, and a group of switches and capacitors to the left, for the antenna matching. To the right is the main wiring, the relays, and tuning motor. Across the back is a horizontal shelf, which supports the 8 removable sub chassis, attached above and below. They screw into place with several long screws, and multi pin plugs. This assembly is screwed into a cast aluminium case, with many peripheral edge screws and a gasket. It is waterproof when the air vents are closed. The controls have glands on their shafts.

T-195 Top View (inductor, capacitor, discriminator, and doubler modules removed)

T-195 Bottom View (PA, servo, dynamotors, and modulator modules removed)

The Auto tune gear set is driven by a DC motor. When a channel change occurs, the motor drives the gearbox, until the HOME position is reached. This involves rotating the MUTI TURN shaft, which is connected to the PTO. This also drives the BANDSWITCH shaft, through 10 turns. The display is rotated through 4 bands, till it reaches 1.5 Mhz. The slug rack is rotated through 1 turn to insert the slugs fully. When the HOME position is reached, the motor reverses. This rotates all the shafts in the other direction. There are 8 slotted rings, which can be set at different positions. When a pawl slips into a cam ring, the motor stops. The auto tune is then complete.

T-195 Autotune Gear Set

The cam ring can be set to a different frequency, by loosening the lock ring, and manually setting the frequency, then retightening the knob lock. Both the frequency knob and the band switch knob must be indiviually set.

RESTORATION
The front panel and radio case were cleaned. All the modules were removed and the upper and lower chassis cleaned.

T-195 Removed Modules

A meter was found for the audio level indication. Apparently the meters and knobs were removed when the transmitter was disposed of as they contained radium. Luckily the missing meter was a VU Audio Level meter so was not hard to find. If the other meter with its individual scale was missing, this would have been much more difficult to locate. All the modules were cleaned and fitted. The interlock switch was disabled. A 4 pin power cable was used to connect to a 28 volt high current power supply. The main switch was turned ON. The meter showed 28 volts, when switched to the battery position. The valves began to light up. There is a time delay of 40 seconds, before the high voltage an keying circuits can be energised.

T-195 Front View (audio meter missing, and dust caps on)

MASTER OSCILATOR LINK
The meter switch, when set to GRID DRIVE, and the KEY switch operated, showed no movement, no grid drive. The oscilloscope was used to explore around the PTO. There appeared to be output from it. The doubler module had no input. I looked at the huge circuit, it was several feet long, and read the manual. It appeared as though there was some sort of link required. Upon investigation, the PTO output came to the front panel connector. This should be connected to the FSK unit, which puts a shift on the PTO frequency for TTY operation. It can be jumpered internally if this is not required. I removed the 2 BNC dust caps, and placed a short U link across the 2 connections. I now had some drive on the meter on all bands, some more than others.

T-195 LONG CIRCUIT

For alignment, the slugs in the slug rack module were adjusted, as in the manual, until there was maximum drive on all bands.

HIGH VOLTAGE DYNAMOTOR REPAIR
There was no PA current. The High Voltage dynamotor was not producing any voltage at all. It was removed and the case taken off. This was a solid state version of the dynamotor, not the older motor and generator rotary type. It was cylindrical in shape, and all the components had been squeezed inside. One of the transistors had failed and burnt out the bias resistor. Both the transistors and both the resistors were replaced. The dynamotor fired up and produced 1000 volts DC, and the cooling fan operated. It was refitted to the chassis.

HIGH VOLTAGE DYNAMOTOR DESIGN
The dynamotor was a rotary design when the transmitter was first produced in 1956, with a normal motor and generator rotary type. This consumed a large amount of current, the transmitter rated at 45 Amps at 28.5 volts DC. When the transistorized inverter type of power supply was fitted, the transmitter current was reduced to 25 Amps at 28.5 volts DC. There were several versions of the solid state dynamotor, and the transmitters were named as T-195, T-195A and T-195B. The new dynamotors were fitted at the maintenance depots, but not all the transmitter nameplates were updated. There are several versions of the solid state design, some using 8 power transistors, some using 6 power transistors, and this version using 2 power transistors. The manual TM 11-5820-335-35 November 1970 has the solid state circuits.

There are many windings on the circular transformer. Each transistor collector has 2 windings in series. Each transistor base has 2 windings in parallel. So there are 8 windings for the operation. On the secondary there are 4 windings, each with a bridge rectifier, and the DC outputs are in series, to produce the 1000 volts DC. There is a 2 uF capacitor at 1200 volts DC as a filter. The fan is driven from these secondary windings with the AC signal. There is a small START circuit using a UJFET to make sure that the oscillator starts. There is also an inductor in the base circuits that sets the oscillator frequency at 540 cps. The main transformer is in a circular metal case. The other components are encased in black epoxy modules, which screw onto the mounting rails.

T-195 High Voltage Dynamotor Repair

Now that there was high voltage for the PA valve, there was some indication of plate current, but not a great deal. It appeared as though the PA auto tune circuit was not working.

The PA amplifier module was removed, and the discriminator diodes, and capacitors were replaced. The servo amplifier valves were checked, and capacitors were replaced. The 400 hz chopper was checked and seemed to be not working. After studying the circuit, it was established that there was no 400 hz coming from the Low Voltage dynamotor.

LOW VOLTAGE DYNAMTOR REPAIR
The LV dynamotor was removed. It was powered up on the bench with a test power supply, but while there was reduced 250 volts DC, and reduced minus 45 volts DC, there was no 400 Hz at all.

T-195 Low Voltage Dynamotor Repair

T-195 LV Dynamotor

The diodes and capacitors are encased in epoxy. The plastic cover was removed and the epoxy chipped away. There were faulty diodes, a burnt printed circuit board, and a shorted capacitor. These were replaced. The 250V, -45V, and 115V 400 Hz were now correct. The LV dynamotor was installed in the transmitter, and now the PA auto tuning system was working. The PA current was much better, but still not high enough.

When in the manual channel mode, you could unlock the oscillator tuning frequency knob, and turn the knob, and watch the PA capacitor automatically move to the resonance position. You could also move the un energised capacitor with an insulated tool, then key the transmitter, and watch the PA capacitor, move quickly to resonance. You could push it either way (against a physical resistance) and the capacitor would return to resonance.

ANTENNA MATCHING
As the autotune system was now working, the next section to investigate, was the antenna matching. The ceramic roller inductor was slowly rolling to one end (filling with turns), then reversing and rolling the tape back onto the shorting cylinder. It was doing this incessantly. The 400 Hz waveform was not a completely pure sine wave, so a small rotary inverter was connected with long wires to 28 VDC, and laid on the bench. It produced a cleaner 400 hz waveform, but there was no change.

The Discriminator Module was removed and the capacitors and diodes were replaced. There was still no change. The servo amplifier module was removed and the valves checked, but they were good. The capacitors were replaced. There was still no change. The waveforms were examined on an oscilloscope, and it seemed as though the capacitor (phasing) servo amplifier was driving the motor, but there was something wrong. It turned out that the motor had an open circuit winding. A capacitance module was purchased, and the motor installed. The capacitors now rotated and the sliding switch went up and down. However, the inductor still cycled back and forth. Careful reading of the manual, gave a trouble shooting chart of what to look for. In section 11 of the chart, it covers the winding and unwinding of the inductor fault. There are 10 possible causes of this fault, and it was number 3, adjustment of the sliding capacitor switch (S1002). This was not adjusted properly and was not operating the linear switch on the "lost motion drive" (S1003).

T-195 Capacitor Switch

This switch was adjusted and the capacitor now went to zero, and the inductor rotated faster, and then stopped in the mid position. It then slowly searched for the correct "loading" while the capacitor module searched for the correct "phasing". They both stopped, and the RED light came on, meaning correct matching. The external rotary inverter was removed, and the internal Low Voltage Dynamotor connected. The correct matching was still occurring, and the RED tuning light was on.

MODULATOR
The audio power output was low, so I decided to substitute a modulator valve as the PA final, to see if the valve was the problem. I pulled out the modulator sub-assembly, and removed the valves. One was cold, the other was hot. I checked the heater resistance and one had an open circuit heater. I checked my spare valves, but did not have any 4X150D valves, so I ordered some. A new valve improved the modulator output.

LOW PA OUTPUT
The PA current on the meter was still low, it should have been in the shaded area on the scale. When the modulator valve was put in the PA socket, there was still low RF output. So it was not the PA valve. The clamper valve controlled the PA screen voltage, and this voltage was low. After the PA unit is removed, then reinserted, the marked red line must be rotated unit it aligns with the chassis mark. Then it can be replaced and the Oldham coupler engaged. Behind the Oldham coupler is a multi humped cam, with a switch that follows this cam. The switch is used to disable the PA amplifier (using the clamp valve) while the band switch rotates. This also ensures there can be no switch contact flashover while changing bands. The switch was checked and found to be out of adjustment. The screws were loosened, and the switch was moved, in a direction around the cam left and right (to assure alignment), and also in and out (to ensure the cam operated the switch properly). A multi meter buzzer was connected across the normally closed contact to achieve this. Then the multi meter was the moved to the normally open contact. This required several different adjustment attempts, until the cam operated both switches properly, and corresponded to the band switch wiper. The PA was now drawing a lot more current, and providing more RF power into the dummy load.

T-195 Band Switch showing the Cam and Cam follower

OUTPUT CAPACITOR FAULT
At the beginning of the antenna matching, a motor rotates the output capacitor switch, to select the correct capacitors. The switch was rotating and stopping correctly. The main switch is a large ceramic type, to select the high voltage capacitors, and there is a small switch for control. This was checked with an ohm meter and it was found that the control switch was not synchronized. The screws were removed, the switch wafer was removed, and rotated to the correct position. The correct capacitors were now selected.

T-195 Output Capacitor Switch Wafer

CIRCLIP REPAIR
I noticed a few washers on the bench, which had not been there before. They appeared to be from the rotary inductor shaft. There is a small clutch on the end, which allows the motor to turn the inductor, but also allows the other motor to turn it as well. I looked around and eventually found the circlip, which should hold them on to the shaft. It was the same colour as the bench top. I refitted them, and added small amount of superglue, to make sure they stayed in place. I am not sure why they fell off, as it was working before.

T-195 Circlips

PA FAULT
While doing further testing, the output inductor began cycling, from one end to the other, rewinding, then starting again. The RED matching light would not come on. I checked the output from the PA to the and there was nothing, no RF at all. The PA servo was tuning the output capacitor correctly, but no RF was getting to the aerial matching circuitry. I checked with an ohm meter and there was a short circuit to ground. I removed the PA module and checked, and the fault was a capacitor C225, had gone short circuit. This was replaced and it all worked again.

T-195 Faulty Capacitor

MANUAL
The manual is comprehensive. It covers the general description of the transmitter, and the operation. It also covers the theory of the autotune and the antenna matching. There are phase diagrams of how the servo amplifier works, and how it drives the servo motors. There are many circuits and diagrams of the modules. There are also instructions on how to remove and service the modules, and how to re insert them. There are descriptions of the mechanical and electrical alignment. There are also diagrams of the 28 VDC distribution, the 115 volt AC 400 Hz distribution, the 250 volts DC distribution, the -45 volts DC bias distribution, and the 1000 volts DC distribution.

CONCLUSION
This transmitter may have been on the shelf, and used for replacing spare modules in faulty transmitters. Any faulty modules may have been substituted into this transmitter. Certainly, many modules had faults. There were many capacitors replaced in the servo and discriminator modules. The transmitter is easy to tune manually, and once the channels are set up, it is easy to change the frequency, or the band in use. It is extremely complicated inside, which allows the external controls to be simplified. It is also heavy and difficult to move, but once setup, it is fine. The power supply does need to provide a heavy current, and batteries or a sturdy mains supply is required. This transmitter is noisy. The blowers on the front panel generate a huge amount of noise.

REFERENCES
TM 11-806 Radio Transmitter T-195 /GRC-19 June 1956
TM 11-5820-335-35 Depot Maintenance T-195, T-195A, T-195B, November 1970
T-195 Transmitter, Dennis DuVall, Electric Radio, issue 104, page 4
Designing the T-195 Transmitter, part 1, Fred Johnson, Electric Radio, issue 113, page 8
Designing the T-195 Transmitter, part 2, Fred Johnson, Electric Radio, issue 114, page 6
Designing the T-195 Transmitter, part 3, Fred Johnson, Electric Radio, issue 115, page 4
Rebuilding the AN/GRC-19 www.radioblvd.com/GRC-19%20Rebuild.htm

There are two videos of the T-195 transmitter in operation, as follows:
tuberadio.com/robinson/Information/T-195_Tune_Success.MTS
tuberadio.com/robinson/Information/T-195_Tune_Success_Internal.MTS

Copyright
Ray Robinson

INDEX