Collins R-388 s/n 58
Collins R-388 is a 30 band receiver that covers 540 kc to 30.500 mc. The receiver will readout out to 1 kc for extremely good frequency accuracy. The band width ranges from .2khz to 6 khz in 5 steps via xtal phasing. The unit is extremely stable. It is designed to receive AM/CW/MCW, you can receive SSB by turning the RF gain control down and the AF gain up. The receiver is the military equivalent to the Collins 51J-3 commercial receiver except it is built to military specifications.
|Frequency range||.5 Mc to 30.5 Mc|
|Receiver type||Single, double or triple conversion superheterodyne|
|IF frequency||500 Kc|
|Number of tubes||18|
|Tuning||Linear, divided into thirty 1 Mc tuning steps|
|Method of calibration||Built-in crystal oscillator (100 Kc)|
|Frequency stability||Over-all stability within 1 Kc for average conditions; within 2 Kc for extreme conditions|
|Output impedances||4 and 600 Ohm|
|Antenna input impedance||Unbalanced to match short whip antenna (50 Ohm, 100 uuF)|
|Power requirements||85 W at 115 or 230 VAC, 45 to 70 cps|
(thanks to Jose, EB5AGV, for the above table)
these pix before cleaning or doing any work (click on pic for full-size)
It's dirty. I rebuilt the filter cap earlier, and powered it up today, 6/16/05. The 5V4 rectifier was bad & replaced. One knob is broken, one has a cracked skirt. All tube shields are in place as are the hold-downs for tubes, filter cap & xtal. The front panel is very nice, there is only one small hairline scratch thru the paint, about 1-1/2" long, at the left of the BFO on/off knob. It hears the 100kc calibrator on all bands, but only faintly hears from the antenna. The PTO is off approx. 8kc from one end to the other, with a fairly linear deviation, it should come in very well with less than a turn removed from the compensating coil.
The PTO has been removed for alignment &
replacement of the bypass and feedback caps if reqd.
All work has been completed, 7/13/05:
The PTO was 7kc short in 10 turns (1000kc), the compensating coil was trimmed, and now the worst deviation between the 100kc points is 0.46kc, it is only 0.5kc off end-to-end, vs the 7.0 originally, very good. The 2 bypass capacitors and one feedback cap were replaced in the PTO. Essentially, if you set the dial at any 100kc point with the calibrator, the actual freq. will not be off any more than 0.46kc by the next 100kc point, and most are much better.
All tubes were tested, 4 replaced with new or ones that test as new. Four "bathtub" capacitors were leaky and were "re-stuffed" with new capacitors. Two, C-205 and C-214 were removed and checked with 600vdc and found to be as good as new, and were not re-stuffed. The filter capacitor was replaced before any work started.
The AC cord was replaced with a 3-wire one, and new AC line bypass caps were installed.
During a full alignment it was found that the 500kc crystal in the crystal phasing circuit was bad, and it was replaced. The receiver has been "burned in," under power for several hours at a time, at least 5 times now. During the 3rd burn-in, an AGC problem surfaced, all of a sudden it was quiet, and the S-meter read full scale. It was the mica coupling capacitor, C-204, from the plate of the detector to the AVC amp. This item has been a problem noted by several R-388 owners, and hadn't been replaced previously as an experiment, which succeeded in showing up the problem again. Now, all problems noted in the initial observations, plus any found during work, were remedied.
It is ready for a new home.
these pix after completion
overall scratch hardly noticeable now top looks a lot cleaner now
bottom corner, upper 2 bathtubs
"re-stuffed," AC-line caps
more general overall shots, showing top and bottom covers, etc.
To see some of my other work on Collins equipment, with the PTO work in
click HERE and HERE and HERE
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And remember: "They don't make tubes nowadays like they used to..."