WARNING: This is preliminary version of manual, I will update it later with pictures, more tube samples, and restoration walk-through. Please note this manual have some Cyrillic writings originally found on these devices, so make sure your browser display them correctly.
L1-3 and L3-3 are among the best and powerful transconductance vacuum tube (valve) testers ever made. They are identical in terms of features but L1-3 uses 5C4M vacuum tube diode instead of solid-state rectifier of L3-3. These testers can be used with almost any commodity vacuum tube imaginable as long as filament current is less or equal to 2.5A – 3A. Twin/combines tubes tested separately, each with its own card board. Parameters are set via perforated card boards (or just using pin # if card is not available), and bunch of switches and potentiometers. L1-3/L3-3 allow test emission, transconductance (using Sergeev’s topology), leakage and reverse grid current.
Manuals of Soviet era equipment are usually unclear, poorly organized, and confusing. For example, one of the most important parameters – maximum rated value of filament current. I have 2 slightly different manuals of L3-3, one states 1.2A and another 3A, in range of 1 – 14V (for L1-3 – only 1.2A). However, in the same L1-3 manual I see tubes approved for testing like 6N13S (6080) and 5C3S with 2.5A and 2.7-3.3A filament current respectively. I’m was able to successfully test on L1-3 twin triode RCA 6080 with 2.5A filament current (line voltage regulator becomes very hot, but this is normal for L1-3).
WARNING: Please perform these steps EXACTLY as described! Failing to do so may damage tester and burn certain components!
Vacuum tubes are powered instantly when you insert them, use gloves to prevent heat damage of skin! Remember, temperature of glass envelope is typically around 200 – 250 degree C.
Remove all pins from the tube parameter setup panel if any.
L1-3 and L3-3 have 2 parameter setup panels with 72 holes each. Further panels will be referred as “I” (top) and “II” (bottom, right above micro-ampermeter).
Put fuse into corresponding slot position (220V, 127V, etc.). Do NOT turn on yet.
Verify if scale is mechanically OK and is in position “0”.
Potentiometers Un (“ГРУБО” and “ПЛАВНО”), Ua, Uc1, Uc2 – left position (counterclockwise)
Rotary switch ИЗОЛЯЦИЯ – position “ПАР”, switch “ПАРАМЕТРЫ” – 250.
Rocket switches “MKA” and “S” – position “ИЗМЕР.”
Open slide doors, turn on tester, and wait for 30 min.
WARNIGN: L1-3 have power line voltage regulator (huge wire-wound potentiometer) located next to the left door. It becomes VERY hot, so be careful!
Preliminary check of voltages
Rotary switch “ИЗОЛЯЦИЯ” – position “ПАР”, rocket switches “MKA” and “S” – position “ИЗМЕР.”.
Checking power line voltage. Push button “СЕТЬ” and use potentiometer (L1-3) or rotary switch (L3-3) “СЕТЬ” to adjust scale to “120”.
Take 5 pins and insert them into 1/I (Uc1 = -65V), 20/I (Uc2 = 300V), 26/I (Ua = 300V), 40/II and 52/II (2x450V)
Checking anode voltage. Rotary switch “ПАРАМЕТРЫ” – position “Ua”. Push ”ИЗМЕРЕНИЕ” and use potentiometer “Ua” to adjust scale to “120”.
Checking 250V voltage (used for system blocks). Push ”ИЗМЕРЕНИЕ” and use potentiometer “250V” on right side (under slide door) of tester to set scale to “120”. Potentiometer is very tough and requires considerable force to turn. Use large screwdriver with insulated handle.
Checking grid #1 voltage. Rotary switch “ПАРАМЕТРЫ” – position “Uc1” (“СETKA” in Russian means “grid”). Push ”ИЗМЕРЕНИЕ” and use potentiometer “Uc1 – 65V” to adjust scale to “65” (absolute value). Remove pin from 1/I and insert into 2/I. Push ”ИЗМЕРЕНИЕ” and use potentiometer “Uc1 – 10V” to adjust scale to “10” (absolute value).
Checking grid #2 voltage. Rotary switch “ПАРАМЕТРЫ” – position “Uc2”. Push ”ИЗМЕРЕНИЕ” and use potentiometer “Uc2” to adjust scale to “120”.
Translation from Russian: “ИЗОЛЯЦИЯ” – “Insulation”, ”ИЗМЕРЕНИЕ” or “ИЗМЕР.” – measurement, “MKA” – micro-ampermeter, “ПАРАМЕТРЫ” or “ПАР” – parameters, “СETKA” – grid of vacuum tube, “СЕТЬ” – power line.
Checking filament voltage
Insert pins 69/II, 70/II (DC filament) and 66/II, 72/II. Then, one by one (one at time!), 21/I, 22/I, 23/I, 24/I, 19/II, 20/II, 21/II, 22/II. Filament voltage (shown on scale without pushing any additional buttons) should gradually drop.
Calibration (to be performed regularly)
First of all, take corresponding perforated card board of any triode, tetrode, or penthode and insert pins. Do not insert any tube!!!
Calibrate transconductance tester (крутизнометр). Rotary switch “ПАРАМЕТРЫ” – position “S”, rocket switch “S” → “КАЛИБР.” Push button ”ИЗМЕРЕНИЕ” and adjust scale to “120” with potentiometer “S“ – “КАЛИБР.”. Then, put rocket switch “S” back into position “ИЗМЕР”.
If its not possible to set “120” value follow 11.12 of L3-3 user manual. Remove perforated card, vacuum tube (if any) and insert pins 20/I, 26/I, 40/II, 52/II. Rotary switch “ПАРАМЕТРЫ” – position “S”, rocket switch “S” → “КАЛИБР.”. Push and keep on button “ИЗМЕРЕНИЕ”, while adjusting potentiometer “ЧАСТОТА” (frequency), located under hatch on left side of L3-3, to 150 (max scale value). AC voltage between pin 4/I must be 450mV (potentiometer “АМПЛИТУДА” – amplitude), to be measured with voltmeter with high (!!!) input resistance. Further adjustments of transconductance meter described in 11.11 of L3-3 user manual.
Set “0” of tube micro-ampermeter and calibrate it.
Turn rotary switch “ПАРАМЕТРЫ” into position “Ic1”. Rocket switch “MKA” turn into “ИЗМЕР.”, push button “ИЗМЕРЕНИЕ” and use potentiometer “0 MKA” – “ИЗМЕР.” to set scale to “0”. If its not possible, use potentiometer “УСТ 0” on the left side next to the slide door. Potentiometer is very tough and requires considerable force to turn. Use large screwdriver with insulated handle.
Turn rocket switch “MKA” into position “КАЛИБР.”, push button “ИЗМЕРЕНИЕ” and use potentiometer “MKA” – “КАЛИБР.” to set scale in position 120.
IMPORTANT! Turn rocket switch “MKA” into position “ИЗМЕР.”
WARNING! It is prohibited to turn rocket switch ‘MKA” and “S” in position “КАЛИБР.” with installed vacuum tube for testing. You will burn several components in tester’s circuit!
Extra tips:
1) If you have difficulty calibrating 0 and 120 of MKA (micro-ampermeter), try the following. Turn rocket switch “MKA” into position “КАЛИБР.”, rotate potentiometer “КАЛИБР.” (on the front panel) approximately into the middle of position, push button “ИЗМЕРЕНИЕ” and use use potentiometer “УСТ 0” (while keeping button “ИЗМЕРЕНИЕ” down !) on the left side next to the slide door to set scale in position 120. Then turn back switch “MKA” into position “ИЗМЕРЕНИЕ”, and use potentiometer “0 MKA” (on the front panel) to set scale to 0.
2) Testers run very hot, especially early versions of L1-3, so they must be used with both slide doors open. Some are subjected to thermal run-away, so calibration (described above) had to be performed once in a couple of hours. It takes only few minutes, however. So before inserting next tube you can check calibration (with any perforated.card board and corresponding pins inserted).
Translation from Russian: “КАЛИБР.” – calibration, “УСТ 0” – setup of “0” (zero point).
Managing Scale Values
Scale on L1-3 and L3-3 takes time to get used to.
Take any perforated cardboard, for example, 6H13C (6N13S)/6H5C (6N5S) – it corresponds to the USA/European 6080, 6AS7, ECC230, TE46, CV2984, 6520 family of twin triodes, and look closely. You will see 3 lines of parameters to be set or measured.
Top:
Un = 6.3V~ – filament voltage
Uc1 = -30V (75) – grid #1 voltage
Ua = 90V (150) – anode voltage
Ukn = 250V – voltage between filament and cathode (discrete setting with pins)
Rk = 120 om (discrete setting with pins)
You need to adjust these variable values after inserting pins and installing vacuum tube for testing. Discrete values are set via pins on parameter setup panels I (top) or II (bottom).
Middle:
Для 6H13C (for 6N13S)
Ia = 48 -:- 80 -:- 112 mA (150) – anode current
Ikn <= 100 mkA (150) – leakage current between filament and cathode
S = 3.9 -:- 5.5 -:- 7.1 mA/V (7.5) – transconductance
Bottom:
Для 6H5C (for 6N5S)
Ia = 25 -:- 60 -:- 95 mA (150) – anode current
Ikn <= 100 mkA (150) – leakage current between filament and cathode
S = 3.3 -:- 4.75 -:- 6.2 mA/V (7.5) – transconductance
Do not overlook small numbers written next to the parameter setup values! This is max measured value which corresponds to the “150” mark on scale! If its 150, it is great, it means scale is absolute (value on scale = real value). If not, scale is relative and therefore, simple math required. For example, for transconductance scale value 150 = 7.5.mA/V
Examples:
Un = 6.3V (15), real value = measured value * 15 / 150, e.g. 63 on scale = 6.3V
Uc1 = 250V (300), real value = measured value * 300 / 150, e.g. 125 on scale = 250V.
S = 3.3 -:- 4.75 -:- 6.2 mA/V (7.5), real value = measured value * 7.5 / 150, e.g. 95 on scale = 4.75
Conclusion:
RV (Real Value) = SV (Scale Value) * K (coefficient from perforated card board) / 150
For quick tests, just to have scale values: SV = RV * 150 / K.
Testing Diodes
Take corresponding perforated card board and insert pins.
Install tube into corresponding socket (its number written on perforated card board in the middle right after word “ПАНЕЛЬ”) below tube model.
Setting filament voltage – use (without pushing buttons “ИЗМЕРЕНИЕ” and “СЕТЬ”) potentiometer “СЕТЬ” (on L1-3) or rotary switch “СЕТЬ” (on L3-3) to adjust voltage to required value – it corresponds to 120 value on scale.
Put rotary switch “ПАРАМЕТРЫ” in position “ИЗОЛ”, and rotary switch “ИЗОЛЯЦИЯ ” into position ”KH”. Push button “ИЗМЕРЕНИЕ”. Read leakage value between cathode and filament (absolute value).
Put rotary switches “ИЗОЛЯЦИЯ” into position ”ПАР”, and “ПАРАМЕТРЫ” in “I выпр.”. Push button “ИЗМЕРЕНИЕ”, and convert relative scale value into real current For example, for 5C4M scale value 78 will translate 78*300/150 = 156 mA, well above minimum.
If particular vacuum diode requires manual adjustment of Ua and Ia, please read below how to setup them (this procedure is identical to all tubes).
Translation from Russian: “KH” (кенотрон) – vacuum diode, “ПАНЕЛЬ ” – socket, “выпр.” – rectified.
Testing Voltage Stabilizers
Note: Scale is absolute in all measurements (value on scale = real value).
Take corresponding perforated card board and insert pins.
Put rotary switches “ИЗОЛЯЦИЯ” into position ”ПАР”, and “ПАРАМЕТРЫ” in “Ua”, turn potentiometer “Ua” into left position (counterclockwise)..
Insert tube into corresponding socket (its number written on perforated card board in the middle right after word “ПАНЕЛЬ”) below tube model.
It should be turned off for the moment.
Rotate potentiometer “Ua” clockwise until voltage stabilizer turns on (ignites). Push button “ИЗМЕРЕНИЕ” and write down scale, e.g. 105V (absolute).
Put rotary switches “ПАРАМЕТРЫ” in “Ia”, push button “ИЗМЕРЕНИЕ”, and set “Ia” equal to min value (written on the perforated card board or in voltage stabilizer datasheet, e.g. 5mA). Switch back rotary switch “ПАРАМЕТРЫ” to “Ua”, push button “ИЗМЕРЕНИЕ”, and read voltage value (e.g. U(Ia=min) = 105V).
Turn back rotary switch “ПАРАМЕТРЫ” in “Ia”, push button “ИЗМЕРЕНИЕ”, and set Ia to max value (e.g. 40mA) with potentiometer “Ua”. Switch back rotary switch “ПАРАМЕТРЫ” to “Ua”, push button “ИЗМЕРЕНИЕ”, and read voltage value (e.g. U(Ia=max) = 109V).
Delta of stabilized voltage is calculated as U_delta = U(Ia=max) – U(Ia=min) – 1. 1V is a voltage drop of scale’s shunt.
Rotate potentiometer “Ua” counterclockwise to the leftmost position and remove tube.
Testing Triodes, Tetrodes and Penthodes
Take corresponding perforated card board and insert pins
Rocket switches “MKA” and “S” – position “ИЗМЕР.”.
Rotary switch “ИЗОЛЯЦИЯ” into position ”ПАР”.
“Uc1”, “Uc2” must be switched in rightmost position (clockwise) to set maximum bias value in order to prevent overheating of tube in testing.
Use rotary switch “ПАРАМЕТРЫ” and potentiometers “Ua” (push button “ИЗМЕРЕНИЕ” on) to set anode voltage to the value specified on perforated cardboard.
Insert tube into corresponding socket (its number written on perforated card board in the middle right after word “ПАНЕЛЬ”) below tube model. Without any buttons pushed, scale shows filament voltage (relative value).
Setting filament voltage
AC filament voltage (for power tubes): use (without pushing buttons “ИЗМЕРЕНИЕ” and “СЕТЬ”) potentiometer “СЕТЬ” to adjust scale pointer to required value (usually, but not always, filament required voltage corresponds to 120 value on scale, look on particular perforated card board for more info) .
DC filament voltage (for small-signal tubes): Use (without pushing buttons “ИЗМЕРЕНИЕ” and “СЕТЬ”) 2 potentiometers “НАКАЛ” → “ГРУБО” and “НАКАЛ” → “ПЛАВНО” to set exact filament voltage. (usually, but not always, filament voltage 12.6V corresponds to 126 value on scale, look on particular perforated card board for more info) .
Translation from Russian: “НАКАЛ” – filament, “ГРУБО” – roughly, “ПЛАВНО” – precisely.
Now its time to test most obvious defects – leakage between filament, cathode and grid(s).
Leakage measurements: Of course, its impossible to measure leakage current between grid #1 and grid #2 in case of testing triodes 🙂
Set voltages “Ua”, “Uc1”, “Uc2” as written on perforated card board. Be sure to check if scale is absolute or relative in order to correctly interpret values!!!
Put rotary switches “ПАРАМЕТРЫ” into position “ИЗОЛЯЦИЯ” (leftmost counterclockwise). Turn rotary switch “ИЗОЛЯЦИЯ” in positions “KH”, “KC1” and “C2C1” to measure required leakage currents (written on perforated cardboard, or may be taken from tube data sheet).
If leakage value is very low (zero or close to zero), hold down button “ИЗМЕРЕНИЕ” and remove pin 38/II (Ukn = 100V) or 39/II (Ukn = 250V). If scale value remains stationary, it means there are no short between cathode and filament.
Translation from Russian: “KH” (катод/нагреватель) – cathode/filament, “KC1” (катод/сетка #1) – cathode/grid #1, “C2C1” (сетка #1/сетка #2) – grid #1/grid #2 .
If leakage current is within allowed range, put rotary switch “ИЗОЛЯЦИЯ” into position “ПАР”, and then use rotary switch “ПАРАМЕТРЫ” to measure anode current “Ia” (emission test), and then perform transconductance “S” test. Do not forget to push button “ИЗМЕРЕНИЕ”!
Slight vibration of scale pointer during transconductance test is still OK, however, jumps at high range means tube is noisy.
Examples
Penthode 6П14П-ЕВ (6P14P-EV), analog of 7189, EL84; tube socket #11, perforated card board “П-6” (P-6).
Top:
Un = 6.3V (15) – DC filament voltage, to be regulated with 2 potentiometers Un (“ГРУБО” and “ПЛАВНО”).
Ua = 250V (300) – anode voltage
Uc2 = 250V (300) – grid #2 voltage (grid#1 voltage fixed, discrete setting with pins)
Rk = 120 om (discrete setting with pins)
Middle:
Ikn <= 20 mkA – leakage current between filament and cathode, absolute scale, Ukn = 250V fixed.
Bottom:
Ia = 40 -:- 48 -:- 56 mA (75) – anode current
Ic1 <= 1 mkA (3) – grid #1 current
Ic2 = n/a -:- 5 -:- 7 mA (7.5) – grid #2 current (no min value)
S = 9 -:- 11.3 -:- n/a mA/V (15) – transconductance (no max value)
Delta (triangle sign) printed on card means that min or max parameter is not specified and in fact can be any below (or above), depending upon range.
I will describe step by step setting for the first example, but skip these obvious matters in the future.
Rocket switches “MKA” and “S” – position “ИЗМЕР.”.
Rotary switch “ИЗОЛЯЦИЯ” – position “ПАР”.
Put perforated card and insert pins into parameter setup panels.
Potentiometer Ua – left position (counterclockwise), minimum value.
Uc2 – right position (clockwise), maximum value.
Potentiometers Un (“ГРУБО” and “ПЛАВНО”) left position (counterclockwise), minimum value.
Insert vacuum tube, and use potentiometers Un (“ГРУБО” and “ПЛАВНО”) to set scale to 63 (6.3V DC filament); it should stabilize within 30 – 60 seconds or so.
Rotary switch “ПАРАМЕТРЫ” – position “Ua”; scale value should be 125 (125*300/150 = 250).
Rotary switch “ПАРАМЕТРЫ” – position “Uc2”; scale value should be 125 (125*300/150 = 250).
Rotary switch “ПАРАМЕТРЫ” – position “ИЗОЛЯЦИЯ”, rotary switch “ИЗОЛЯЦИЯ” – position “KH” (leakage current between cathode and filament); scale value 19, real value 19 mkA, max allowed value 20 mkA, test (almost) OK. If leakage value is very low (zero or close to zero), hold down button “ИЗМЕРЕНИЕ” and remove pin 38/II (located in the middle). If scale value remains stationary, it means there are no short between cathode and filament.
Rotary switch “ИЗОЛЯЦИЯ” – position “ПАР”, rotary switch “ПАРАМЕТРЫ” – position “Ic1”; scale value 29, real value 29*3/150 = 0.58 mkA, max allowed value 1 mkA, test OK.
Rotary switch “ИЗОЛЯЦИЯ” – position “ПАР”, rotary switch “ПАРАМЕТРЫ” – position “Ic2”; scale value 126, real value 126*7.5/150 = 6.3 mA, allowed range 5 -:- 7 mA, test OK.
Emission test. Rotary switch “ИЗОЛЯЦИЯ” – position “ПАР”, rotary switch “ПАРАМЕТРЫ” – position “Ia”; scale value 90, real value 90*75/150 = 45 mA, range is 40 (low), 45 (average), 48 (high), test value is OK.
Transconductance test. Rotary switch “ИЗОЛЯЦИЯ” – position “ПАР”, rotary switch “ПАРАМЕТРЫ” – position “S”; scale value 102, real value 102*15/150 = 10.2, test OK.
Scale values for quick emission & transconductance tests:
SV = RV * 150 / K
SV f(Ia) = 80/96/112 (low/average/high)
SV f(S) = 90/113 (min/max)
Twin triode 6080, analog of 6H13C (6N13S), 6H5C (6N5S), 6AS7, ECC230, TE46, CV2984, 6520; tube socket #7, perforated card board “H-20” (N-20) for triode #1, “H-23” (N-23) for triode #2.
Top:
Un = 6.3V~ – AC filament voltage, to be adjusted with potentiometer (on L1-3) or rotary switch (L3-3) labeled “СЕТЬ”, 6.3V will correspond to the “120” on scale..
Uc1 = -30V (75) – grid #1 voltage
Ua = 90V (150) – anode voltage
Ukn = 250V – voltage between filament and cathode (discrete setting with pins)
Rk = 120 om (discrete setting with pins)
Middle:
Для 6H13C (for 6N13S)
Ia = 48 -:- 80 -:- 112 mA (150) – anode current
Ikn <= 100 mkA (150) – leakage current between filament and cathode
S = 3.9 -:- 5.5 -:- 7.1 mA/V (7.5) – transconductance
Bottom:
Для 6H5C (for 6N5S)
Ia = 25 -:- 60 -:- 95 mA (150) – anode current
Ikn <= 100 mkA (150) – leakage current between filament and cathode
S = 3.3 -:- 4.75 -:- 6.2 mA/V (7.5) – transconductance
Look at the perforated card board “H-23” (N-23) for triode #2. In the middle it lists 2 parameters: “*S >= 2.8 mA/V” and “*Ia>= 30 mA”, noted with asterisk “*”. If your tube tests above these values, it means it still have long life expectancy before being worn out.
We take values for Russian 6N13S, which is the same as 6080 but uses different glass envelope.
Ua = 90V (absolute value)
Uc1 = 60*75/150 = 30V
Ikn = 50 mkA (absolute value) <= 100 mkA, leakage current between cathode and filament test is OK.
Ia = 85 mA (absolute value), well above average, emission test is OK.
S = 120*7.5/150=6, well above average, transconductance test is OK.
Scale values for quick emission & transconductance tests:
SV = RV * 150 / K
SV f(Ia) = 26/60/98 (low/average/high)
SV f(S) = 70/100/130 (low/average/high)
WARNING: Some early runs of 6N5S have manufacturing defect – short between cathode and filament, so perform “KH” test ASAP after installing tube!
Beam high-frequency tetrode 6Ж3П (6J3P), analog of 6AG5, 6BC5, 6CE5, EF96, 6186
tube socket #10, perforated card board “Ж-19” (J-19), “Ж-20” (J-20), “Ж-21” (J-21).
Perforated card board J-20 (testing leakage, emission, transconductance, and grid #2 current)
Un = 6.3V (15), Ua = 250V (300), Uc2 = 150V (300)
Ikn <= 25 mkA (Ukn = 100V), *S >= 3.25 mA/V
Ia = 5.2 -:- 7 -:- 8.8 mA (15), Ic2 = 1.3 -:- 2 -:- 2.7 mA (3), S = 4:- 5 -:- 6 mA/V (7.5)
Scale Values for Ia = 52 -:- 70 -:- 88
Scale Values for Ic2 = 65 -:- 100 -:- 135
Scale values for S = 80 -:- 100 -:- 120
Perforated card board J-20 (testing leakage and grid #1 current)
Un = 6.3V (15), Uc1 = -2V (3), Ua = 250V (300), Uc2 = 150V (300)
Ikn <= 25 mkA (Ukn = 100V)
Ic1 <= 1 mkA (3)
Scale value for Uc1 = 100
Scale value for Ic1 <= 50
Perforated card board J-21 (Iaxb)
Un = 6.3V (15), Uc1 = -9V (15), Ua = 250V (300), Uc2 = 150V (300)
Iaxb <= 30 mkA (30)
Scale value for Uc1 = 90
Scale value for Iaxb <= 150
Penthode 6Ж4П (6J4P), analog of 6AU6, EF94, tube socket #10, perforated card board “Ж-25” (J-25), “Ж-26” (J-26),
Perforated card board J-25 (testing leakage, emission, transconductance and grid #2 current)
Un = 6.3V (15), Ua = 250V (300), Uc2 = 150V (300)
Ia = 7.7 -:- 11 -:- 14.3 mA (15), Ic1 < 0.5 mkA (0.75), Ic2 = 2.8 -:- 4.5 -:- 6.2 mA (7.5), S = 4.8 -:- 5.7 -:- 7 mA/V (7.5)
Perforated card board J-25 (testing leakage, emission, transconductance and grid #2 current)
Un = 6.3V (15), Ua = 250V (300), Uc1 = -5V (7.5), Uc2 = 150V (300)
Ia < 1 mA (Iaxb) (1.5)
Beam tetrode 6P1P (6П1П), analog of 6AQ5, EL90 and the 6V6, tube socket #11, perforated card board “П-7” (P-7).
Un = 6.3V (15), Ua = 250V (300), Uc1 = -12.5V (15), Uc2 = 250V (300)
Voltage on both grids are regulated (no discrete values).
Ikn <= 30 mkA (150), Ukn = 250V – voltage between filament and cathode (discrete setting with pins)
Ic2 <= 7 mA (7.5), Ic1 <= 1 mkA (3)
Ia = 33 -:- 44 -:- 55 mA (75), S = 3.8 -:- 4.9 -:- 6 mA/V (7.5)
Scale value for Ua = 125
Scale value for Uc1 = 125
Scale value for Uc2 = 125
Scale value for Ic1 <= 50
Scale value for Ic1 <= 140
Scale values for Ia = 66 -:- 88 -:- 110
Scale values for S = 76 -:- 98 -:- 120
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