EB5AGV's TV-7 Voltage Alignment Instructions
Keep them glowing!
This procedure was developed from some notes Dan Nelson, the TV-7 expert, sent me some time ago in order to align my TV-7C/U. I sorted all the info I got in an easy-to-follow way... I hope you can use it to get your TV-7s to specs!. Any questions will be welcomed. As usual, BEWARE WITH HIGH VOLTAGES PRESENT IN THE UNIT. Don't do it if you are not confident.
VOLTAGE ALIGNMENT IN A TV-7 TESTER
-Plate load: 375K resistor between pins 3 and 6 in octal socket (plate load).
FILAMENT and PLATE adjust
GRID, LO SCREEN and HI SCREEN adjust
- (1) Put the filament voltage in the .6 volts position and set the line for .652 VAC on the filament with no load (measure voltage between pins 2 and 7 in octal socket).
- (2) Place the filament voltage on 10 volts and measure 10.04 VAC
- (3) Place the filament voltage on 117 volts and measure 117 VAC
- (4) Arbitrate the above to the best setting for all.
- (5) This should produce a LINE SET condition. Adjust the line set to agree, by means of a calibration pot on the bracket hanging off the function switch, R134 (this is only present in TV-7D/U units. Check LINE SET resistors in any other model and replace them if out of tolerance, to get the right meter deflection).
- (6) Final Check, for most TV-7 units, the actual PLATE DC voltage will then be 153-154 VDC (measure voltage between pins 3 and 6 in octal socket).
And that's all!. Now you should have a voltage calibrated TV-7. Next step is to calibrate the transconductance (gm) readings. I'll post this method as soon as possible... stay tuned!.
- (7) Then, if the plate voltages and the filament voltages resolve themselves, the rest can be worked out by fixing the tap setting on the resistor on the terminal board by the transformer.
The taps in R130 control GRID, LO SCREEN and HI SCREEN voltages.
It is important to adjust the various voltages in the proper order as they interact otherwise. First do the GRID voltage, then the LO SCREEN voltage, then the HI SCREEN voltage. All of these can only be done after the LINE SET has been negotiated and can be used as a reference. Voltmeter is assumed to block AC and read only DC. 375K resistor is between cathode and plate. The Voltmeter must be arranged between the electrodes involved
in the setup. Thus for a setting of HS5-3460
- PLATE Volts measured in octal socket: '-' Pin 6 , '+' Pin 3
- GRID Volts measured in octal socket: '-' Pin 6 , '+' Pin 5 (negative values)
- SCREEN Volts measured in octal socket: '-' Pin 6 , '+' Pin 4
- (8) GRID adjustment: Turn up the grid control all the way, to 100. Then adjust tap interior most to produce -40.0+-2 VDC. A second check should be made with the dial set at exactly 22. The grid volts should be -3.0+-.2 VDC. Play with the tap so that the spread is best.
- (9) LO SCREEN adjustment: Set the bias dial to zero. Set the voltmeter for the SCREEN voltage. To adjust the LO SCREEN voltage to 56.0+-1 VDC, adjust the next tap from the one used to adjust the GRID. Measure by pressing button 2+3 at the same time.
- (10)HI SCREEN adjustment: Set the bias dial to zero. Set the voltmeter for the SCREEN voltage. Adjust the tap nearest the end of the R130 resistor (only in TV-7D/U). If there is none, insure that the voltage is 130+-3 VDC when you press button 3.
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