WA8ULG - Ted
Parks-Flagstaff, AZ
Back to Phoenix AM Page
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The
current Big Project at WA8ULG: converting a Collins 820 D2 1-kW
broadcast transmitter to HF operation on 160, 80 and 40 meters. The 820 D2
("The Rock") runs a pair of 5-500's in the final, modulated by a pair
of 5-500's. |
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The Tank is a Pi-L using an effective 1100 pF Plate C, 15 uHy, motor-driven variable L and 4000 pF Load C. The coil on the floor of the tank box is the L of the Pi-L; it is fixed in each band. The PA Tank covers 160/75 and, tentatively, 40. The Plate C is a 2000 pF in series with the 4000 pF vacuum variable that nicely opens the range up over the nominal tuning for 160 and 75. When typically run at 3855kHz, component values are: 400 Pf Tune, 5uHy and 1700 Pf Load. |
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Driver
input circuitry: A Philips PM-5192 Synthesizer is used as the
oscillator. It comes into the box at TTL levels.
A 74xx something drives a 2N3866 that, in turn, drives an
MRF-150 FET which drives the final grids through the input
transformer. The 160 input transformer is the original coil cut
down; the 75 coil is new and on the Delrin pier shown to the
right. Everything switches, the primary on the left side
of the relay and the secondary on the right side. The 40-meter
section is yet to be installed. (Click here for larger photo ~100K) |
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The
Tuning and Loading controls: The two multi-turn knobs control
the
plate-tuning cap (top) and the loading cap (bottom). The
bat-handle switch in the old PA tune hole operates in conjunction with
the little edgewise meter to control and follow the Pi inductor (15
uHy). The front panel unlabeled knob to the right of the load
multi-turn is the band switch. (Click here for larger photo ~100K) |
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Posthumous Statement by Art Collins,
W0CXX, Concerning This Modification |
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A
subassembly in the Nye-Viking tuner falls victim to the
plasma-generating CW power of "The Rock", as well as its asymmetric,
positive-modulation capability. Click here for larger picture |
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The
latest addition is a Radio Engineering Associates AMM-HF1 modulation
monitor, situated between the Collins 51J4 receiver and the Philips
frequency synthesizer. Click here for larger picture |
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Click on Icons at left to see Mod Monitor and 51J4 in action with WWV signal. | |
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A product shot of the REA AMM-HF1. This unit displays both positive and negative modulation levels on the two, green LED "meters". It can be used to measure transmitted and received signals, although the latter requires additional IF amplification. Click here for larger picture Click here to go to the REA website |
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The complete WA8ULG AM rig: (r-l) receiver/mod monitor/synthesizer (vfo); 820D2 xmtr; audio rack. Click here for larger picture |
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The audio rack: GR 1931 modulation monitor, Shure Audio Master mike
preamp/driver, decade-adjustable audio pad and a 3-band, IMP-3 compressor/limiter. Click here for larger picture |
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WA8ULG at the mike. 5-500 finals and modulators shown, as well as modded RF-driver circuitry. Click here for larger picture |
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FORT TUTHILL redux |
WA8ULG leads the charge to return the ARCA hamfest to Flagstaff (Ft. Tuthill). Read all about it here.... | |
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