mcmurdo Masterpiece VI Alignment Instructions

A L I G N ME N T I N S T R U C T I O N S M A S T E R P I E C E VI
In the accompanying photograph all circuit alignment trimmer adjustments found beneath the
chassis are identified as to circuit end purpose. It should never be necessary to realign a MASTERPIECE
VI in the field due to the use of air alignment trimmers and permanent, non-varying coils and wiring.
I. F. AMPLFIER
The I.F. amplifier alignment will require an oscilloscope, a frequency modulated R.F. generator,
and an output meter. The oscilloscope and generator should preferably give the double trace pattern and
have a total frequency modulation of 40 kc. (20 kc. below and 20 kc. above 465 kc.)
First using a 400 Cycle amplitude modulated 4 kc. signal from the generator applied to the 6L7
first detector grid, fidelity switch first in 4 kc. position, then in 32 kc. position, align all I.F. transformer
trimmers so that maximum deflection is obtained on output meter, making certain that the I.F. and R.F.
AVC trimmers are detuned so that the AVC's will not affect alignment.
Second, connect oscilloscope ground connection to tuner chassis and the input terminal of
oscilloscope to the junction of resistors R17L and A17K in the cathode circuit of the 6J5 second detector.
Substitute the 40 kc. frequency modulator signal for the 400 cycle amplitude modulated 465 kc. signal
, place the fidelity switch in 32 kc. position, and wave switch in B band position with the dial tuned so that
no interfering signal will destroy the scope pattern.
Turn the grid trimmers of I.F. transformer T5, T6, T4, one complete revolution each separately
(see picture of chassis for designations). Each grid trimmer (G) will have one point at which there we'll be a
minimum output (smallest pattern on scope). Adjust all grid trimmers, T5, T6 and T4 to this position,
increasing the signal input from generator as necessary to keep a visible pattern on scope. Next adjust all
plate trimmers (P) of T5, T6, and T4 unti1 a single trace is obtained having a single "hump" and maximum
output (at 456 kc. resonance) MAKE CERTAIN THE T5, T6, and T4 PLATE TRIMMERS ARE NOT
TOUCHED AGAIN DURING ALIGNMENT.)
Now adjust the grid trimmers (G) of T5, T6, and T4 until the picture shows a single trace double
"hump" pattern of maximum output. It will be necessary to decrease signal as these trimmers reach proper
alignment, and it will require retrimming of T5, T6, and T4 grid trimmers only two or three times before a
perfect picture is obtained. DO NOT TOUCH THESE TRIMMERS AGAIN.
To align transformer T3 throw fidelity switch to 8 kc. position and adjust T3 trimmers P and G
until a single trace double "hump" picture is obtained which has greater selectivity than obtained before.
DO NOT TOUCH THESE TRMMERS AGAIN.
Transformers Tl and T2 should be aligned by throwing fidelity switch in 4 kc. position and
aligning the trimmers of Tl and T2 until maximum signal trace pattern of extreme selectivity is obtained.
Increase signal from generator to approximately ½ volt and adjust the trimmers of R.F. and I.F.
AVC until pattern decreases to a minimum. This will give proper alignment of I.F. and R.F. both AVC's if
properly carried out.
To set Beat Oscillator, turn the treble control to the left until the switch clicks. Then adjust the
Beat Oscillator trimmer until a zero beat is obtained when one-tenth of a volt of 465 kc. unmodulated
carrier is applied to grid of 6L7 first detector.