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TV-7's meter:
I have purchased TV-7 tube testers whose meters stick or just do respond to line adjust .
A 100uF 15V electrolytic capacitor, C103 connected in parallel with the meter is sometimes leaky or just shorted. I replaced them with a newer types of caps and two insulated standoffs.
 Capacitor and Standoffs
Most of the meter movements I have worked with have been Phaostron type 200uA movement. Inside the meter housing is a calibrating resistor which is 1.9k-Ohm to 2.1k-Ohm in series with meter coil which is only installed on TV7 meters. I have purchased the same meter type Phasotron 200uA meters and then added the resistor and changed meter scale plate with the old TV7 scale. The meter is calibrated by connecting a resistor decade box in series with meter and setting the TV7 switches to HS5-3460, Bias to 0 and Shunt to 0. Connect a 375K-Ohm load resistor in parallel with multimeter from pins 6 and 3 of the Octal test socket. I use a digital multimeter with the 375K-Ohm load resistor or a 1k-Ohm/volt analog multimeter without load resistor, both will give accurate calibrations. Adjust line adjust for 150 Volts +/- 3volts by depressing pushbutton 3 Mut. Cond. Then press Line Adjust pushbutton 1 and adjust decade box for meter needle to center line, the resistance should be 1k-Ohm to 3K-Ohm. Add resistor to meter on the inside or outside of meter housing. Most analog meters used on Mil type equipment are sealed and their enclosures say "do not open sealed". If you have a sticky meter you have no choice but to fix or replace meter. The meters can be opened by removing ten screws around rear meter flange. remove meter bezel and pry meter face off there is a rubber gasket between meter glass and flange. First move pointer needle with tooth pick find where meter sticks, sometimes due hard impact the needle will bend down and contact meter scale. If needle is contacting scale pry needle up a bit until needle clears scale. If you have loose matter in movement it can get between magnet yoke and moving coil. Some matter is case material and can be magnetic or non-magnetic. I use Miller-Stephenson T-P 35 MS-160 which is spray Isopropyl Alcohol and is Carbon Dioxide propelled. It will not leave any residue and will not harm most plastics. Remove meter scale by removing three screws from scale, be careful not to loose needle limit bumpers and slide meter scale by sliding out from under needle without bending it. Spray a stream between moving coil and magnet to wash out debris. If the debris is magnetic push it off with tooth pick were it be remove with needle nose pliers or a tooth pick with a layer of tape rolled with the sticky side up. Try to get debris to stick to tape for removal. Wash out with TP-35 and let dry for few hours. Check for operation and re-install scale, meter glass and bezel. Some meter pivots are just worn out from years of service( pivot friction ) and cause meter not to repeat its calibration position and should be replaced. A sign of this wear is when you tap the meter face with your finger to settle the needle into its final position. Its a good idea to add some meter protection to you tv7 meter. Connect two 1N4001 diodes back to back and solder to the rear lugs on the back of the meter. This clamps the maximum voltage that can appear on meters terminals to 0.7V. This will reduce the chance of meter movement due to over-load.
 Two diodes for protection
Broken R130: I came across TV-7D/U tube tester that R130 was open. R130 is used to develop the Screen Voltage +130V, Diode test Voltage +56V and Bias Voltage +40V from the plate Voltage +150V, . If any part of the resistor is open between any of the taps you will loose a voltage. The problem with finding the resistor is not the value ( 9.5K-Ohm ), but its the length. A standard resistor size is to short for so many taps. I re-engineered the divider using standard 12 watt resistors and also gives a greater adjustment range on the "A" tap +130V. The original resistor is very hard to adjust because the "A" tap is very close to the end. With the modification the "A" tap's extended calibration range of the +130V can be adjusted very accurately. TV-7/U and TV-7A/U serial number 1-1200 use a standard 12 watt resistor that can support two taps. TV-7A/U serial numbers 1200 and higher use the longer R130 resistor as well as TV-7B/U, and TV-7D/U.
 Three power resistors to replace R130 and extension bracket.
Bad R102, R103 and R104: Check these resistors for correct value. Which are located on the Grid/Plate/Screen rotary switches. I replaced a handful of these over time. The old carbon comp resistors do change value do to age and improper tube testing. They are 47-Ohm 1 Watt resistors +/- 5% tolerance. If they are damaged you may see the resistor has a bulge at the center, but check them with your digital multimeter anyway. I replaced them with NTE® 2W047 47-Ohm 2 Watt flame-proof resistors. They are the same mechanical size as the old 1 Watt, but they can handle overloads without changing value and are very stable. Remove old resistor and put Teflon® tubing over leads of new resistor , cut and bend leads to match old resistor. Its very tight around switches, so be careful not to put to much force on the switch wafer lugs. Cut out old resistor and leave 1/4 " old lead to help of removal of lead from lug. Use a solder sucker to remove old solder from lug and bend out old resistor leads from lug. Insert lead in lug and re-solder.
Solid state replacement for 83 tube: I have used this mod in my TV-7D/U, use solid state replacement for the number 83 rectifier tube. Use an old 4 pin tube base, two 1 amp 1000 volt rectifiers, ( 1N4007 ) and a pair of 10 ohm 1 watt resistors, ( NTE® 2W010 ) . This will save about 15 watts of internally produced heat in the case of the tester and end the problems with the mercury vapor rectifier: If you install this mod you will have to recalibrate your tester.
 Solid state 83 tube replacement
Technical Manuals
- Operator's and Organizational Maintenance Manual, Test Sets, Electron Tube TV-7/U, TV-7A/U, TV-7B/U, and TV-7D/U
Department of the Army, TM 11-6625-274-12, June 1960
- Field and Depot Maintenance Manual, Test Sets, Electron Tube TV-7/U, TV-7A/U, TV-7B/U, and TV-7D/U Department of the Army, TM 11-6625-274-35, 30 June 1960
- Organizational, Direct Support and General Support Maintenance Repair Parts and Special Tools Lists for Test Sets, Electron Tube TV-7/U, TV-7A/U, TV-7B/U, and TV-7D/U
Department of the Army, TM 11-6625-274-24P, November 1979
- operational Supplement, Technical Manual Field and Depot Maintenance, Electron Tube Test Sets TV-7/U, TV-7A/U, TV-7B/U, and TV-7D/U US Air Force, TO 33AA21-5-32S-1, 20 September 1973
- Operational Supplement, Technical Manual Field and Depot Maintenance, Electron Tube Test Sets TV-7/U, TV-7A/U, TV-7B/U, and TV-7D/U
US Air Force, TO 33AA21-5-32S-2, 25 January 1978
- Test Data for Electron Tube Test Sets TV-7/U, TV-7A/U, TV-7B/U, and TV-7D/U
Department of the Army, TB 11-6625-274-12/1, 17 January 1962
or US Air Force, TO 33AA21-5-31, 17 January 1962
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