[R-390] Newbie looking for Calibration Instrument(s)

[Roger Ruszkowski]

Dave, Tom is right the crystal calibrator two volt meters and a 600 ohm resistor is all that is needed to get the receiver aligned.You can listen to the receiver on the 100 KHz call tones and get a pretty fair alignment.If you have the feel for where your knee is on both sides of the peak point, you can sweep the adjustment a couple times and leave it setting in what you feel is the peak point.Fellows, with feelings can walk a receiver in at over 95% of the next pass with generators and counters.Your ears verse your ears and meters 4% difference. (We young men with ego's and near free beer and cigarettes  did in in the shop by the hours. How do I deliver max with minimum effort.) The difference is touch time. R390's are toys that encourage you to learn hands on physics.  Any RF signal generator that will modulate a tone onto the RF carrier signal will work. AN/URM 25 signal generators are surplus used working and often under $50.00 at swap meets. Postage for shipping can be expensive. These were the Army units we used every day in the shop. I gave two children a bath and cleaned them up for the next six months each night shift. Or I gave ten others and all the little troubles their collective monthly maintenance time for the night shift. On day shift you were gone or on detail and not maintaining receivers in a field station. On detail was maintaining the field station campus. Contractor watch.There is a whole series of AN/URM 25  production models the later D, E, F models are liked as having gotten better over time. The fit and function are the same but all insides do not mix and match interchangeably. See the R390 and R390/A receivers as an example of equipment production models compared to the contract build of a production lot of model A receivers. You over haul and align these AN/URM 25 beast with a meter and alignment tool. You zero beat against a bunch of broad cast stations. A DC gain set adjustment sets the generators output level and is metered on the generator. Just purchase one and us it. Frequency counters are under a $100.00 new from China and will count the generator output frequency to the cycle for you. (Isn't a frequency counter and signal generator a dongle and phone app?) Generator out put level is relative and exact micro volt output level is not necessary. If the generator functions it will exceed your maintenance requirements. Dial to frequency and dial to output level are only nice distractions. Your R390/A receiver is your frequency standard. It was designed and built that way. A DC voltage is metered to indicate maximum peak tuned frequency zeroed against the band pass of the IF deck 455 crystal. In a world of RCHs the band pass notch of a crystal is not necessarily exactly the same as the crystals oscillation frequency. The R390 IF deck .1 KHz band pass filter crystals have their own part number. The difference is in RCHs and we do not care. If your IF deck crystal is missing (common event) or not working, you install a 455 Khz crystal and if it will adjust up it is good to go. Chuck Ripple tells us to not stress on the exact IF gain adjust. Because once you have a receiver all aligned and adjusted up by the numbers, you set the IF deck gain adjust by ear to your ears. It is your ears, it is your receiver, personalize it for your comfort. I find I happen to like a -5.5 volt set up. 150 micro volts of 455 into the IF deck for -7 volts on the DC load is a set point for a uniform maintenance procedure. We can all use common set up values and compare receiver performance between receivers using a repeatable measurable set of metrics and processes.But when you are all done set the gain on the noise knee by ear. Listen to your receiver you will learn to hear vacuum tubes amplify. Think of vacuum tubes adding water marks to all the images it processes. Copy to Roger by 6C4 V202. We crop the image size with filters to remove some of the water mark artifacts. We adjust the contrast to minimize the water marks visual impact. At 10 to one the receiver water marks are below hearing. Over 20 to one is expected and receivers today are doing 30 to one. (A lot of new better performing capacitors are the main point of gains.) 25, 26, 27, 28, 29 are subjective meter reading. But you know a better alignment by the difference in the meter readings. A fine group of folks in the last century working to a dead line produced the best reading of all the manuals that hangs out virtually all the time at ---https://www.r-390a.net/Y2K-R3/index.htm--- The debunked debured walk it down the line what and why 30 page ISO quality inspection check list is at ---https://www.r-390a.net/AI4NI-Checklists.pdf--- I have been attempting to first learn and then teach leading edge technology since I dodged the draft back in 68. Want to be authors and owners support group members have been gracious and shared their wisdom from experience and you guessed it those pearls of wisdom files are at ---https://www.r-390a.net/Pearls/index.htm--- It popped in the news last week that make a wish foundation with a real cash exchange had a trial balloon up for as many as 70 new owner operator maintainers in the Amateur Radio community.   End point adjustment on the VFO is tough and a concession was made for a frequency counter in the depot shops. Procurement screwed up the R390 IF deck sweep generator procurement. The wrong plug in front end was ordered. The wanted 455 KHz module was not included in the procured and delivered property book items to the field stations. R390 IF deck alignment with a sweep generator never went past state side demonstration because the needed parts were not procured to implement the practice on the receivers operating around the world. Vietnam, Korea, Okinawa all were missing the magic low end module. Not on the books, never arrived, not on the TOE (Table of equipment). Some one thought we wanted to sweep align the RF deck in the Receivers and provided HF modules. Compressed air and a wash tank for 50 cal and smaller items designated for TTY and Mill maintenance were nice additions to field station depot shops. At stations where we carried you walked into the shop on duty time and cleaned it in the maintenance shop oil room. A ventilated wet floor, sink, compressed air, solvent wash tank washing machine room. Set a mechanical typewriter in there and go to lunch. Drip dry, blown dry, wipe up with paper towels going into a burn bag. Old ribbon into a burn bag and a new ribbon installed. Semi annual maintenance on a type writer. Then the typewriter maintenance man tuned the machine to the best of his abilities to reduce machine friction for the operator. You stick your fingers in my receiver and I will stick my fingers in your Mill. We all got along on some simple seniority and accepted social customs. Union shop floor rules to military standards. A nice place to work and prosper if you want to get along working and playing well with others. Help these new guys become your on line pen pal community centered on a vacuum in a tube. Last week the subject was lame VU meters. Since I had last combed my ISO check list I had encountered two field mods not covered in the published edition of my ISO check list. The need here is for heuristics that share what we know with the younger students with the least friction.Dave, ask how much signal generator.Tom, said none because a good alternate no cost solution exists and cited the alternate solution. Tom took the mystique and bull out of it for you Dave. A straight up real answer that works. ---https://www.r-390a.net/AI4NI-Checklists.pdf------https://www.r-390a.net/Y2K-R3/index.htm------https://www.r-390a.net/Pearls/index.htm--- Respectfully, Roger