I conducted an initial "Survey of
the transmitter in the middle of the
living room floor the next day. No rectifier
tubes on the Power Supply deck, Humm, ok I have 3B28s no problem. I
flipped
the deck up on the H.V.
transformer end and checked the bottom wiring, lots or splices and
inter-lock
bypasses. I brought up a 20 amp
120 volt variac for the HV transformer primary, and a 10 amp 120volt
variac
for the 3B28 filament transformer.
made a few jumpers to get around the interconnect requirements, and
plugged
in a pair of 3B28s and turned them
on. After a few minutes I applied ac to the HV transformer primary and
got 300 VDC out of the power supply
components. I set my HV Digital VOM up and turned the ac on the HV
transformer,
and without any load
on it the power supply got up to 3000 VDC as measured on the Fluke VOM
with HV probe. OK so far the
thing isn't totally "DEAD". Now if you try this at home, "a note of
caution", First make sure you put an
insulator in the HV shorting switch at the rear of the chassis, I used
a piece of Teflon rod 3/16 inch diameter.
Second, make sure that the two variacs are set to 0 that is zero volts
output on the dial. The relays on the
chassis do not matter at this time. Step one apply AC volts to the 3B28
tubes, count to ten, then slowly
bring up the AC volts to the HV transformer. I attached the test leads
before applying any power, so as to
leave both hands free for controlling the Variacs, one for each hand.
The next test was of the Speech Amplifier on the Modulator
deck. I removed
it from the "MOD" deck and
took it to my work bench. Setup my low-voltage power supply to run it
and
provided a load for the driver
transformer hooked up the 'O'-scope across the load and pumped in audio
from a HP-200CDR. There was
a 5814 tube missing which was replaced with a "NEW" 5814. I swept the
audio
range from about 200 Hz to
about 3500 Hz. All looked good on the 'scope so I let that go for the
time
being. The specified range is 300
to 3300 Hz so I felt the speech amp was working well enough for now.
Next came the Modulator deck itself. The main portion of the
modulator
deck had NO, (nada, none) tubes
on it. Hum, well I have enough parts to build one of these things, lets
check the manual and see what we need.
The list consisted of (3) 5R4GY, (4) 0A2, and (2) 4-125A. Which turned
out to be RCA, GE, and Eimac tubes
from the TUBE STASH. Drag up the shops' high voltage supply, a couple
of
variacs for 120 VAC and a load for
the modulation transformer output. Put it all together, fire it up and
see if anything smokes. No smoke, dump audio
drive to the input of the deck and look at the load for signal output,
viola, this is working also.
One interesting
aside about the speech amp and its mounting. When I connected it to the
modulator deck it was laying on the
work bench at the far end of the bench, the modulator deck itself, was
holding down the right side of the test
bench. I connected the metal of the speech amp chassis to the metal of
the Mod deck and all went well for the
test. However when I mounted the speech amp in its correct place on the
mod deck, it seemed intermittent. A
check of the harness to the speech amp showed the ground was broken off
inside the connector housing, repair
however did not cure the problem. when I was remounting the speech amp
is when I noticed the reddish color
in the mounting holesm using a .22 cal. cleaning brush cleared the
holes, and scotch-brite for the screws and the
intermittent went away.
