Typical Meter Readings; Pa Capacitors C117, Cl23 - RCA BTA-250M Instructions Manual

TABLE
3
TYPICAL METER READINGS
METER Ml04
CIRCUIT
METER METER
Ml02 Ml03
CURRENTS
POSITION
SWITCH
CORRESPONDING
s105
TO 100%
METER READING
Oscillator cathode, VI
1 30
ma
Buffer-driver grid, V I 0 I
2 3.5
ma
Buffer-driver cathode, V 10 1 3
65
ma
PA grid, V102, Vi03
4 25
ma
PA cathode, V102 5 150
ma
PA cathode, V103 6 150
ma
I st AF cathode, V104, V105
7
8.5
ma
Modulator cathode, VI 06 ( 100 s
mod.)
8
150
ma
Modulator cathode, V I 07 ( I 00 R
mod.
)
9 150
ma
Primary, filament transformers
10
100
volts
PA plate current 250
ma
PA plate voltage 1,450
volts
Connect the jumper on coil L 103 as follows:
535-640 kc-Use full coil
640-790 kc-Tap I
790-980 kc-Tap 2
980-l 200 kc-Tap 3
1200-I 420 kc-Tap 4
1420-1620 kc-Tap 5
Make sure the MOD and PA circuit breakers are
in the OFF position.
Remove the plate cap from
one rectifier tube, type 866A.
Operate the PLATE
circuit breaker, S104, to the ON position. This
applies plate voltage to all tubes, but plate current
should flow in only the low power tubes.
2,
Rotate the METER switch, S 105, to positions 1,
and 3 and note the current readings on meter
Ml 04. Meter readings should be approximately
100% ; however, readings from 80 "/o to 120 "/o are
normal. If th e b ff
u er grid current is low or the crys-
tal is sluggish in starting, shut off all power and read-
just the oscillator plate choke tap.
If the frequency
monitor output jack, JIOI, is not loaded, the buffer
grid current may be excessive.
duced by adjustment of RI 12.
Current may be re-
After th e oscillator
and buffer stages are func-
tioning satisfactorily,
Connect the PA tank
open the PLATE breaker.
capacitors Cl 17 and C 123
and adjust L105 tank coil shorting tap as indicated
in Table 4 and Figure 3.
Disconnect the coupling
tap on LlO5 and reconnect it one turn from the
grounded end of the coil.
The harmonic filter and antenna coil shorting taps
and the harmonic filter capacitors should now be
adjusted as described under the succeeding heading,
"Output Circuit." This subject is treated separately
due to the calculations involved, but adjustment
should be made at this point.
Having made the output circuit calculations and
adjustments, operate the PA circuit breaker, S103,
to the ON position and again close the PLATE
breaker switch. Quickly tune the PA to minimum
plate current by rotation of the PA TUNING knob.
The PA PLATE CURRENT meter should indicate
TABLE 4
PA CAPACITORS C117, Cl23
BAND COVERAGE
CAPACITORS CONNECTED
535-600
kc
Cl17,C123