RCA_Superadio_-_Repairs and_modifications_2000.pdf

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1、Friday, 10 November, 2000 FOR ALL INFO. GE Superadio FAQ Appendix A: Repairs and Modifications Superadio II Mods Disassembling the Superadio II Summarized from comments by Bruce Bacon, Ralph Brandi, R. Hardin, and Gregory Doerschler Remove ALL knobs in front, including the tuning knob, by pulling th

2、em straight off. A plastic fork is a good tool to use and wont bend the shaft. Be patient but firm-the knobs may be glued or taped on. Remove the back screws, except the antenna screw. Dont forget the screw in the battery compartment. Remove the front cover by pulling it from the rear and upwards so

3、 that it clears the power switch. The power switch is fragile, and a real bear to fix if you break it, so be VERY careful here. You may want to try removing the button from the switch carefully-or else pushing it in so itll clear the case. If you do break the switch, here are R. Hardins instructions

4、 for repair: The power switch is very entertaining to reconstruct, especially if you dont have all the pieces. Unscrew it, take off terminal plate if its still on (mine wasnt), find little metal slider thingy that grips the terminals on the inside - it slides between terminals 1 and 2, or 2 and 3. T

5、here might be two of them, I only found one; shake the radio over some surface where you can find it when it falls out. Put it on terminals 1 and 2 (the off position). The mechanical parts can be removed now for experimentation: The button, switch case, and a plate with a funny wire in it thats supp

6、osed to be in the back of the switch. Theres, what, 8 ways to try assembling it. Well, 4 ways if you consider that POWER ON OFF has to be legible from the front of the radio, and only 1 way if the plate is still in the case. Put in plate with wire, put in button, and see if the button then has two p

7、ositions its happy in, on and off. (If you have a plate and a wire, instead of a plate with a wire, there are more ways to try I guess.) Leave the switch in the off position, which is the only one its really stable in without the terminals on, and put the terminal plate on, the slider fitting into t

8、he slot in the button. You may have to spread the fingers that were supposed to keep the switch case together a bit. See how nice the switch works now? Screw it back in, and swing case back on, putting it on the top first and swinging it closed. Theres a little forcing past the tuning shaft. Stress

9、the tuning shaft, not the power button! Fixing the Dial Calibration on the SR II by Bruce Bacon: Ive had my SRII for a couple of years now, primarily tuning on the MW side of the dial. The SRII is a great MW DX machine except for one main drawback-dial resolution. Last weekend, I made a modification

10、 which has made the resolution much more livable. If youre into taking radios apart, give the following a try: CAVEAT: If you havent had an SRII apart before, be very careful with the power switch. Take careful note of what it looks like before removing it! I gave up and installed an NCR receipt pri

11、nter rocker switch (P/N 006-1050121). Much better, but a bit of a hack. Remove the knobs from the front of the chassis (volume, bass, treble, tuning). Remove the 6 screws from the back of the chassis. Remove the screw from the battery compartment. Rock the handle and the chassis should split open (w

12、atch out for the power sw). The speaker wires connect both sides of the chassis, so be careful. The pointer is a piece of plexiglass with an orange colored stripe in the middle. You wont be using the orange stripe anymore for frequency identification, youll use the left side of the plexiglass! Find

13、yourself a suitable scribe (I used an exacto knife). The receiver should still operate (careful with the power switch) even though its opened up. I used batteries to reduce the chance of electrocution. Turn the dial shaft and start identifying stations. Using the scribe and the left side of the plex

14、iglass, make a vertical mark every 50Khz (550Khz, 600Khz, 650Khz, etc). Be careful to tune the centerof each station! I made a double vertical line for each 100Khz marker (600Khz, 700Khz, etc.) I guess you could get fancy and make a mark every 10Khz, but I think the dial face would get too crowded.

15、When youve finished with your scribe marks, you can button it back up. Ive found by using the scribe marks in conjunction with the left side of the plexiglass, parallax is virtually eliminated. Frequency identification is much easier. The main thing is to take your time and make sure the frequency y

16、ou think you are on is the frequency you are on! Improved FM Filter Modification, SR II by Ralph Brandi: Ive found it a worthwhile modification to the Superadio II to replace the stock ceramic bandwidth filter (230 kHz? 280?) with a narrow filter 150 kHz wide. It doesnt improve sensitivity, but it d

17、oes wonders for selectivity. For instance, with the 150 in, I can now receive WXPN-FM in Philadelphia, 88.5, (not well, but well enough) right next to local powerhouse WBGO-FM in Newark on 88.3. I got my filter from a friend, along with some articles in the hobby press from a couple of years ago. Th

18、e source I have listed for 150 kHz ceramic filters operating at an IF of 10.7 MHz is: Hosfelt Electronics, Inc. 2700 Sunset Blvd. Steubenville, OH 43952 (800) 524-6464 Part # 27-109, $1 I understand theres a minimum purchase, but I dont know what it is, since I didnt get mine there. Im lucky if I gr

19、ab the correct end of the soldering pencil, but I installed mine this past weekend. I installed a Radio Shack IC socket in place of the old filter (8-pin wire wrap, cut in half and with one pin removed, then cut off the excess wire), then plugged the new filter into the socket. The filter is a littl

20、e tough to get to; its on the second PC board under the dial. It basically involves disassembling the entire radio, more or less. Its right next to a square metal box-shaped thing as my friend with the filters put it (yes, Im electrically incompetent). Things to beware of: Dont break the power switc

21、h. Its a bear to put back together correctly. Make sure you remove the tuning dial from the outside before you open the radio. Despite the radios best efforts to fool you into thinking that it doesnt come loose, it does. Dont mess with the dial cord. If it comes loose, its a pain to get back on, if

22、you can figure out how it goes. Of course, you shouldnt infer from this that any of this happened to me. :-) SR II Front End Repair Michael.B.Haydencc.gettysburg.edu (Michael B. Hayden) writes: My SRII was zapped big time by a proximity lightening strike. The AM section was killed, but FM is OK. I r

23、eplaced the first transistor I came to in the front end with the first thing I came across in the junk box, but the SRII is now just a radio rather than a Superadio. It lacks decent sensitivity indicating the replacement transistor is not a good match for what was there. Does anybody have the schema

24、tic for the SRII and could tell me the specs for the first couple of transistors in the front end section (just in case the first was not the only one to blow. Many thanks, Mike Hayden haydengettysburg.edu Mike, I looked at my repair documentation for my SRII (model 7-2885F) and found, or inferred t

25、he following information: AM RF Q5 silicon NPN bipolar transistor, plastic TO92 type case with an ECB pin configuration looking from the non-leaded side and the flat portion of the package under the ECB pin labelling as in ECB. The replacement transistor is listed not as a 2Nxxxx transistor type but

26、 as cat. no. EA15X2024, available from GE. Parts and service information are given in the Technical Information section of the FAQ. This transistor feeds directly into the IC chip that does the rest of the signal processing, so if anything else is zapped, it might be the IC. It doesnt sound like thi

27、s from your description though. From a practical standpoint, this same transistor is used in the RF amp stage for the FM portion of the receiver, and is biased at 1ma/3v for the AM section and 0.6ma/3v for the FM section. These bias points, and use as the FM RF section indicates that the transistor

28、needs to have a good FT, on the order of 200-300MHz at fairly low current, so something like the common 2N2222 transistor would likely give poor results. The BVCEO break down voltage need not be much higher than 10 volts as there is a simple internal regulator for the collector voltage. The other un

29、known here is the capacitance spec of the part for collector-base capacitance. Being in the tuned RF stage, the part might spec a low cb capacitance. I cant tell this from the information that I have. With this information, I would look for a small signal 2N. number with BVCEO 12v, and FT specified

30、at low currents, around 1ma. This type of transistor should be readily found in the small signal RF transistor listings for several manufacturers. A transistor fiting this category which should work is the 2N918. It is a metal TO18 4 lead transistor with one lead connected to the case. This case lea

31、d can be left floating, or preferably,cut off. Hope this information helps you out. Mail me back your experience with this repair when you are done. Fred Superadio III Repairs and Modifications Sensitivity Fix for some Superadio IIIs From the March 1993 edition of DX Ontario: Dave Maunder of Brigus,

32、 Newfoundland, has had some interesting experiences with his Superadio. He writes, Although an R-5000 is my workhorse, Ive often used a GE Superadio II for medium-wave listening. When the Superadio III became available last fall, I ordered one from Universal Radio. Anxious to do a side-by-side compa

33、rison with the old model II, using only the built-in ferrite rod antenna for the test, I was disappointed to find that my new model III exhibited a high background noise level and much poorer sensitivity. So I disassembled the Superadio III to do a little tweaking, and was surprised to find that per

34、formance instantly improved when the 2 halves of the cabinet were separated by the length of the speaker connecting wires. The noise level dropped drastically, and the sensitivity came way up. I now could easily hear VOUS, a 50-watt U.S. Armed Forces station in Argentia, Nfld, on 1480 kHz, and St. P

35、ierre-Miquelon on 1375 was easy. (This at 1:00 p.m. local time at my home about 40 miles from St. Johns.) But when I reassembled the radio, performance deteriorated to the original level. There seemed to be some kind of interaction between the speakers in one half of the case and the circuitry in th

36、e other half. I suspected that it was the strong magnetic field saturating the antenna rods ferrite core, so I wrote GE asking if they had a fix. They seem aware of the problem, and suggested simply reversing the two leads from the circuit board to the speaker unit. I was skeptical, but I tried it a

37、nd their cure worked perfectly. Not only is the GE Superadio III a hot MW-band receiver, (British, German and many other European MW stations are audible nightly here on the edge of the North Atlantic, especially when using my 100- foot long wire) but, on strong signals, the audio in the wide positi

38、on is exceptional.indeed, very close to FM quality in range and clarity. Perhaps this tip might be useful to someone else who buys a GE Superadio III. Not all units may be affected, but if the noise floor seems high and sensitivity poor, try reversing the speaker leads! SR III Power Switch Fix and D

39、ial Light Bill Bonner: I read the FAQ about the Superadio and decided to buy one. I bought the Superadio III. Of course, I broke the POWER switch taking the radio apart. After I saw it was hopeless to fix the switch, I went down to Radio Shack and bought one of their small slide switches which fitte

40、d in the hole left by the broken switch and could be held in place with the same screw. The part number for the switch is 275-409. The disadvantage of this is that you have to reach your finger into the hole left by the POWER switch to turn the radio on and off. The advantage is that the radio does

41、not inadvertently get turned on in baggage, etc. The Superadio III is held together by 7 screws in the back, six visible and 1 in the battery compartment. The tuning knob on the side and the volume and 2 tone control knobs on the front pull off. The 3 slide switches on the front do not need to be re

42、moved. The POWER push button also comes off; it is held on only by friction helped by a little piece of tape (no kidding). I did not learn this until after I broke the switch. The front and back separate with everything but the speaker going with the back. I also bought a small 3 ball bearing rotato

43、r for lazy-susans at a hardware store and screwed it to the bottom of the radio so it rotates with a feather; great for nulling AM stations. I put stickem felt pads on the bottom of the rotator so it wouldnt mar furniture. One surprise was that the rotator worked well for FM. By extending the FM rod

44、 horizontally and rotating the radio, I could pick up two stations on several of the frequencies I tried; Baltimore vs W.Va for example from here near Washington DC. I also found the lack of calibration annoying on AM. I measured the distance in mm for the pointer every 50 kHz (helped by a digital r

45、adio I admit) and drew the lines on white paper with a number below every 100 kHz. (I actually used DrawPerfect which will transfer measurements without distortion, but a fine tipped felt tip will do fine.) I cut out the strip of paper and taped it to the black plastic runway behind the pointer. It

46、works well during the day; the lines and numbers show up fine through the AM and FM windows. I also found it annoying that the radio had no light to use in the dark. I am used to a Sony SW7600 which has a light which goes on for 5 sec when you press the button. I wired a tiny 12v lamp from Radio Sha

47、ck through one of their tiniest momentary push switches. The part number for the lamp is 272-1141 and 275-1571 for the push button switch. I placed the lamp with tape on top of the runway; there is just enough space for it to fit when you put the cabinet together. I drilled out one of the two guide

48、holes for the POWER button used to use and placed the switch in it. I ran wires from the battery pack contacts (9v) for power. The light switch is next to the new slide power switch. The lamp though dim gives enough light on the white paper to easily see the dial placement at night. I may wire two 6

49、v lamps in series to cover the dial scale better. As you can see, this radio has brought out the tinkerer in me. I hope some of these ideas are useful to other Superadio fans. I can often pick up WOR 710 kHz, WFAN 660 kHz, and WCBS 880 kHz during the day at listenable levels. Bill Bonner Comments on SR III Alignment Paul Nix: Has anyone else found the dial calibration on the GE Super Radio III unacceptable? Electronic Equipment Bank (EEB) has sent me two radios now, and the 2nd is worse than the f