the R-390A mechanical filter R390A IF Deck Alignment (Chuck Rippel) R390's made after 1954 and those with mod 2 stamped on the IF chassis have a field change installed to the mechanical filters. Filter input and output trimmer capacitors have been added. The 4 input trimmer capacitors are found by removing the 2 square can on top of the IF chassis using the single nut in the top. The 4 output trimmer capacitors are located behind 4 holes in the left hand side of the IF deck. The IF chassis will need to be loose but still electrically connected to complete these procedures. An accurate counter, analog VTVM and a signal generator capable of outputting 455.00 KC, is required for these alignments. Connect the VTVM to the Diode Load bus on the rear and configure it to read a negative voltage of approximately -7vdc. Set the receiver FUNCTION control to MGC, BFO to OFF and the LOCAL GAIN control to a comfortable level. Lift and tilt the IF deck resting the front captive (green) screw over the front panel. You should be able to gain access to the mechanical filter trimmer capacitors through the large ventilation holes in the main chassis. Locate the cable running from the rear of the IF deck to the *IF OUT* BNC connector in the rear panel, upper left side. Unplug the cable from the IF deck only. Also unplug J-513 and the one next to it. Plug the cable running from the rear IF Out jack into J-513 on the IF deck. Connect the output of your 455.000 kc generator. Mechanical Filter Alignment- •Set the 455kc generator output level to cause the VTVM to read about -2.5V. •With the IF deck oriented so that the bandwidth control is towards you, set the bandwidth to 2Kc and align 1 of the four top trimmers. •Adjust C-569 which is at 9 o'clock for a peak on the VTVM. •Align the output trimmer in the left side of the IF deck, labeled C-567 •Set the BW to 4KC •Align the top trimmer, C-568 located at 12 o'clock •Align the side trimmer, C-566 located at rear, bottom. •Set the BW to 8kc •Align the top trimmer, C-570 located at 6 o'clock. •Align the side trimmer, C-565 located at front, top. •Set the BW to 16kc •Align the top trimmer, C-571 located at 3 o'clock Align the side trimmer, C-564 located at front, bottom. <snip> ------------------------------------------------------------------------------------------------------------ Date: Thu, 9 Oct 1997 23:19:22 +0500 Subject: Re: [R-390] Mechanical filters & insertion loss > Subject: [R-390] Mechanical filters & insertion loss > > The 16 Kc filter in my R-390A seems to have maybe 10 or 20 dB more > insertion loss than the other three. When I switch to 16, the signal > strength meter drops noticeably and the audio level drops a bit, too. It > clearly has more bandwidth than the 8 Kc filter. Listening, it is entirely > believable that it is a working 16 Kc filter, but I can't say for sure > whether or not its bandwidth conforms to the specification. Have you set the trimmers at the top and bottom of the filter? I forget the "C" numbers but there are a series of trimmers on the top of the filters and under the 2" square can which are the inputs and another series of trimmers on the side of the IF deck next to the side of the radio. Run 455kc into J-513 about 10mv and then peak each of the trimmers for both the input and output on each filter. While you are at it, with 455.00kc going in, center up the BFO knob to the exact center of the scale on the front. That way, when you tune an AM signal, zero beating it with the BFO will have the benefit of putting the received signal into the center of your passband which you just peaked on that same 455.00 signal. Be sure to use an ANALOG VTVM on the diode load jumper in the rear to peak the filter trimmers and NOT THE Carrier Meter. The Carrier Meter is far to coarse the see the whole peak. Then set the IF gain such that with no antenna, the LINE METER switch set to -10, the LINE GAIN at "10" or max then peak the ANT TRIM on the internal noise of the RF deck. Turn the IF GAIN pot back so the receiver noise (NO ANTENNA!!!) reads -10 on the receiver. This a rough place to set that by which you can realize maximum sensitivity. If the ANT TRIM does not give you a peak on the noise, the RF deck has a problem. At the very least, you should see the noise peak up on the LINE LEVEL Meter. ------------------------------------------------------------------------------------------------- Date: Tue, 28 Oct 1997 09:42:17 +0000 From: crippel@... Subject: [R-390] Re: Why filters go bad - viz. bad caps It's C-553, the 0.01 plate blocking capacitor for V-501. Its too low a voltage to begin with; a condition aggrevated by the multiplicity error caused by the high voltage transformer. That Vitamin-Q cap shorts and the B+ then has full run of any mechanical filter selected and opens the fine wire inside. Since the frequency involved is 455kc at that point, change C-553 to a 600V 0.01 Orangedrop. ------------------------------------------------------------------------------------------- Date: Tue, 28 Oct 1997 17:40:08 -0600 From: Tom Norris <badger@...> Subject: Re: [R-390] (R-390) Why filters go bad - viz. bad caps Now THERE is a thought to doubly keep DC off the filters. Might give it a try. Hmmmm. Chuck, you tried it -- looking a the schematic, I see no reason it wouldnt work. Suggestions for a good value for that cap? Another .01 or higher? ------------------------------------------------------------------------------------------------------------ Date: Wed, 29 Oct 1997 10:42:08 +0000 From: crippel@... Subject: Re: [R-390] (R-390) Why filters go bad - viz. bad caps Change that .01 to a single .01 Orangedrop at 600V and forget about it. There are space considerations unless you slop the cap in. The capacitor should nestle neatly in a vertical position, against the aluminum sides, in the inside corner of the filter output compartment in front of the bulkhead mounted coil and next to the switch. Double caps won't fit properly in the space allotted. Remember, proper lead/component dress is important. ---------------------------------------------------------------------------------------------------------- Date: Mon, 10 Jan 2000 12:25:52 -0600 From: "Dr. Gerald N. Johnson, P.E." <[email protected]> Subject: Re: [R-390] Distortion / IF alignment Aligning the main IFs for maximum gain at 455 KHz may compromise the widest mechanical filter. Peaking the AGC IF only helps control the signal at the AM detector which is where the distortion was happening. ------------------------------------------------------------------------------------------------------- Date: Sat, 18 Mar 2000 07:20:21 -0000 From: "Phil Atchley" <[email protected]> Subject: [R-390] IF Amplifier or Oscillator, that is the question. Well, I re-capped the IF deck after which it is now a oscillator <grin>, squeals, squalls and makes its presence known. But first a little history.I believe this unit had problems before I started as it sometimes seemed "squirrely" adjusting the RF gain would "peak" somewhat before full clockwise position with a very sharp noise peak like it was oscillating out of the bandpass. Somebody had been in the IF section, rewiring parts of it with far less than "Collins" workmanship. When I re-capped the unit the gain came up noticably but now the oscillations are very apparent. I have checked, double checked and triple checked the little beast, even re-wired all the circuitry around the mechanical filters which was the worst case of wiring I'd seen in a long time. The oscillations "appear" to be centered around the 2nd IF amplifier V502. Removing the tube shield from V502 helps some but not completely. Removing the shield from T501 is even more effective in reducing or removing the oscillations. (Aren't shields supposed to eliminate these spurious oscillations??????) The unit "appears" to have all "Q" reducing resistors in the transformers intact so far as I can tell. Can't measure them in circuit. If I put an antenna on it and tune in a station it won't oscillate, telling me that reducing the gain by the AGC helps. I replaced every tube in the unit one at a time in case one was gassy, no help. I did a search on the CD ROM for oscillations, one fellow had a simular problem and his had an incorrect gain control, replacing the IF Gain Control and adjusting it cured his, not so in my case. H E E E L L L P P P................... This one is giving me more grey hair, that is, what hair I have left. <grin> ----------------------------------------------------------------------------------------------------------- Date: Sat, 18 Mar 2000 19:32:59 -0000 From: "Phil Atchley" <[email protected]> Subject: [R-390] IF Oscillation Cured ! Well, it looks like I finally got this puppy stabilized. Not sure exactly which part/ work did it as I tackled the job "in mass", shotgun style. We all know how hard it is to troubleshoot the IF as the cable harness just reaches and really doesn't lend itself to troubleshooting in operation, though I suppose if you want to stretch things a little you could try. Here is what I did. 1. Completely re-wired the bottom side of the mechanical filters, making sure they were grounded good. The wiring was a mess.