I discovered something. Never watch a radio alignment video when you have a headache. Makes head hurt a lot worse. But it’s still better than watching the news.
13:54 Holy crap! What a precise job of soldering those surface mount caps! I kept staring at the screen. Took a full minute of replays to actually see it. Amazing. Like those pictures where you can see the elephant in the moire if you keep studying...
I worked months ago on a 1963 Sharp BP-301 pocket radio and it had the same problem, this same insane gain and distorted sound, whistle everywhere when trynig to peak the tranformers, a total nightmare. So I started to change some resistors here and there and it started to do less noise, however still super sensitive. I changed the IFs transistors by very similar ones and worked great, maybe the old transistors was noisy who knows? And the last thing I did was to change the value of the avc resistor to get a perfect gain balance. Man, what you did was incredible, so tiny thingy. Thank you very much, this is amazing.
Coupling is ONLY via the top capacitor. The walls do NOT allow the em field through. 2.1pf makes sense, so does 21pf, NOT 260pf. Schematic should show the shield can dotted lines between the two coils. Not getting a peak probably means wrong value caps used. Note that the top cap will determine the bandwidth of the IF, and also flatten out the tuning if too large (coils will interact in tuning if top cap is too large). Motor boating is probably a bad bypass cap.
Philco was a big contractor to the US government for electronics, especially in satellite construction. They heavily invested in transistor technology for their work, something that passed down to Ford's automotive electronic fuel injection as those systems were designed and built to mil spec (with the odd exception of their ignition pickups which had high failure rate). Nice to hear Philco's old transistors are still good, and that their consumer goods were along the quality of what they put in their aerospace equipment.
I don't think this is silver mica disease. It may be semantics, but I define SMD as metal migration on silver across the surface of the mica induce by high voltage (90 volts) attraction. The resulting leakage currents from plate of preceding stage to grid of succeding stage generally sounds like a lightning storm approaching. This radio did not have that sound. All I noticed was tarnishing of the silver surface, and suspect if you had polished with a pencil eraser and reassembled and tightened the clips the transformer woulda been good to go. I'm skeptical that transistor radios with their low voltages (>12 volts) will have enough attraction to cause the silver to migrate across the mica surface. I could be wrong on this point. I'm not sure if the two aluminum (nonmagnetic) cans will act as a faraday screen to electrostatically reduce high frequency coupling, while allowing lower frequency electromagnetic coupling. You have definitely noted too much RF gain. I had this trouble with a Zenith Royal 275. The .05 mf local oscillator coupling capacitor ( a disc ceramic) had turned into a 22 K resistor. Hard to believe but true. Check Beitman's Volume R-20 (1960), page 179. You will note C15 from LO coil to low end of antenna coil. Leaky cap raised base bias by about 1 volt. Radio still played, local stations had splattering audio. I have a Royal 450 that has a bad 2nd IF output transformer. The internal 250 pf cap went open. I tacked 2 100pf + a 50 pf across the tranformer and it tune right up, and had good sensitivity. After several months of use the radio died again. I had to unsolder the caps under the transformer. Apparently, tin whiskers formed joining the internal cap back in circuit, but with resistance in series. As such, the radio works now, but lacks sensitivity. I'm just not brave enough to do microsurgery on the transformer. It sits on the kitchen windowsill and plays talk radio. BTW, you are one tenacious mofo!
@@garbleduser That page # was for the Zenith Royal 275. Shango's T75-124 is in Bietman's 1959, page 105. His radio has an autodyne convertor (no separate local oscillator with coupling cap into mixer), so actually, I gave Shango some useless info. His radio apparently has no RF AGC, only IF AGC. I notice the detector is a transistor, prolly a detector and AGC amp. My only reccomendation is to check bias on RF, IF, and Det/AGC amp. If that uncovers nothing, try bridging a resistor from neg. side of C4 (AGC filter) to emitter of RF Amp. Maybe he could get some delayed AGC action going.
I needed a video like this in the eighties, when I used to fix radios, kkkk. You are the best in this area, I loved your attentin to the details, keep going.
I recognize this as my Dad's old "shaving radio". We lived very close to a Philco Plant in Sandusky Ohio. I often wondered if this radio was actually built there. All the Best! DE W8LV BILL
When that mica wafer came came out, it reminds me of a dentist when he does a root canal when he pulls out the root and he looks at it with a smile on his face and says to you " That didn't hurt you now did it ? "
Congratulations Shango nice work. The gain was above average, the distortions in the sound must be some resistor with value changed in the rf step, but checking all is more guaranteed. But the master is you, always with new challenges. Hug.
The IF capacitors are not that critical in value, once you are able to peak it, it should work. No way the motorboating could be caused by them. And the small 2.6pF is really that low, its value should be Ccoup = Ctune × BW / Fif /sqrt(2) = 160p × 10.5kHz / 455kHz /1.414 = 2.6pF. (Assume that LC pair is designed for flat top with the Q=60 of both LCs)
This^. It’s a double tuned circuit, capacitively coupled. The value of that cap affects the Q and coupling factor. A cheap spectrum analyzer would be well worth the money for this.
Great job, Shango066, on soldering those tiny surface mount caps! I'm sure I can no longer see well enough to do that little tiny work anymore! My hands are still steady, even though very arthritic, but my close vision is terrible for tiny things, even with magnification!🙃🙄
The coupling I think mostly is through the 2.6pF cap. The aluminum shields probably act as pretty good shields at 455 kHz. There might be some magnetic coupling but I think they rely on the 2.6pF to do most of the coupling. You want to lightly couple the two halves to preserve good overall bandpass repsonse. If you ever look at double tuned (2 tank circuits) with a top coupling cap the top coupling cap is always pretty small. Also, those old style 2.6pF type ceramic caps are pretty reliable unless mechanically damaged.
I love that SMD stuff for experimenting at VHF and UHF, you can slap your circuit together any way you want (just keep it small) with no regards given to parasitics. It just works... But after a certain age, you need to work under a microscope with it
I had a radio like the one you are showing,when I moved all but some radios and players came with me but not that one it worked but it needed recapping to it but it worked but distorted sound.
Mica a very soft material to even place in an old Philco radio...........in the first place. I am staying away from extremely old radios with Silver Mica Waffles in them. I love religning old radios just for a fun pastime. An Excellent loud alignment noises from that Philco Radio.. Working on an old large 1970 Japanese "Silver" Boombox myself. RE-Winding a new S.W. and A.M. antenna for it. Nice old A.M. Philco Radio. I have to replace a mica tuning transformer in the tuning circuit, that I burnt with my soldering gun by mistake. Good Luck on your repairs there. Bye Now ! Maybe Connecting a sound generator to the back antenna section may help alignment not really sure ??..... When I was 8 years old, I did it to my old Radio Shack Citizen Radio, and it aligned perfectly. Spray that Frequency Turner box capacitor with some WD-40 maybe.....???? Mod it some how ??? It's to peak up and needs backing down a bit maybe in the gain. Could even be in the A.M. Ferrite antenna maybe ??? Crack-Co Box Radio.
I have a fat stupid.... Philco radio with silver mica disease. I still listen to it a little here and there. It's a model 51-1730 the kind people don't keep. I saved it from the dump. It sounds good even with the 6 or 8 inch speaker all of the way on the floor. Atop it sits my Philco electrostatic deflection 50-701 Bakelite TV. I guess I have to fix them both! Plus the phono with all of the dried up rubber parts. Wish me luck.
Wouldn't it be cool if the schematic indicated proper values for these in can mica capacitors. Guess the manufacturers figured the sets would not last long enough to require this repair. Thanks for another trinco-twinkulate tutorial, Shango! That radio is a classic...........
Back in the day it was presumed that if a component such as an interstage transformer failed you would order a replacement from the manufacturer. Nobody would attempt to fix those.
I feel you. I live in Switzerland - there is exactly one physical store for electronic parts in the country (Zurich). Everything else is online. So if something is really exotic i might have to have it shipped from fricken Minnesota (Digikey).
I’m sure that’s what happened. Radiotvphononut ties two capacitors (or resistors) together to get the correct value quite often. I’ve had to do it myself before.
maybe need to 'stagger tune' those IFs so bandwidth isnt so sharp, and that'll also reduce gain peak,, something like last IF 455, one of that pair 457 , other 452 ??? i've seen service info on some valve/tube sets state you should stagger tune their IFs ....? sometimes the manuals say you 'damp' one coil with a resistor while adjusting the other, then do opposite, also gives wider bandwidth and less sharp peak gain
The problem is that you are peaking both coils to 455 kHz. You have to obtain more like an inverted U shape than an inverted V shape. You have to peak one coil to around 454 kHz, than the other coil to around 456 kHz, this is reducing the overall peak gain, but also assures a wide enough bandwidth for AM reception which also means less distortion. Keep in mind AM bandwidth is 10 kHz and you can't obtain such a large bandwidth by peaking both cans to 455 kHz. Your method of alignment is suitable for DX when want to obtain maximum performance in rural areas, but in some cases when the coils have high Q it is not suitable for distortion free reception, in such cases you have to detune one of the cans to obtain a higher bandwidth (some manufacturers add a 20-200k resistor across the coil to have a higher bandwidth, in this case you don't have to detune it).
I have one of these that sort of worked when I picked it up. While Turing the volume up, it stayed at one level until turned to 75%, then overdrove. After spraying the pot with cleaner, all it does is motorboat now. I suspect a bad transistor, but am trying to figure out how to test it w/o having to desolder.
Curious about the cap between the 2 transformers on the good radio. What value does it measure? Swap the 2 transformers from good to anti good... Hook up the fancy gear and get a visual on those signals.
Would a bad emitter bypass capacitor affect a collector current (let it run higher, as they are intended to provide negative feedback on collector current variance) and yield an increase in a stage gain?
Puzzled over your mystery cap. 2.6pF would be red, blue, gold. 0.26pF would be red, blue, silver. Hard to see on the video exactly what that 3rd band colour is. Sometimes seems partly silver, other times just missing.
Literal translation of how soviet engineering tradition calls these bandpass LC networks is "concentrated selection filter" ("фильтр сосредоточенной селекции" or abbreviated "ФСС"). They used them extensively on most popular and on top of medium price range consumer receivers, especially on models with drum band switch as on tuners of old TV sets, but one can find them in even some smaller or pocket size radios. Soviets, as far as I know, never used mica wafers inside cans, so there never was such a problem with them. Some of the well known soviet receivers with rediculously complex IF filter networks were VEF-12, ~201 to ~206. Even more complicated were filters of Ocean models 209 to 216 and their export brand equivalens Selena with banks of 10 coils, 2 groups in paralel of 5 sequential for AM/FM that were not even switched but used the "magic" property of high and low friquencies not to "see" each other wile navigating LC networks.
Yep that's why the Soviet stuff is badass. Mostly just broken sodders and open capacitors. Never even played with the alignment on one and they kick the crap out of most other radios
The bandpass-filter is kind of 2 single resonant circuits with coupling-capacitor and no inductive coupling, there a some other possibilities to couple 2 resonant circuits, this is called "capacitive headpoint-coupling", "capacity footpoint-coupling" is common in some tv-sets between tuner and if-amp. Some kind of coupling can be seen here (german site): www.radiomuseum.org/forum/abgestimmbare_bandfilter_mit_konstanter_bandbreite.html 2 guesses about the motor-boating: If the capacitor in the AGC is open, if-amp may generate motorboating under strong signal because of no-linear processing with overdrive, then saturate, AGC brings signal down and overdrive again... sometimes you have 2 different AGC-circuits with 2 diodes to get rid of overdrive. .... second guess ist: For an if-alignment the front-end oscillator has to be quite (variable cap has to be shorted), because in this simple superhet-circuits the mixing stage is combined with the oscillator! (self-swinging-mixing-circuit). There can be strange effects under strong signal, too, if this stage is coupling with if-signal of high amplitude. "gain out of control" - this may cause the motorboating ! I think, it must be easy to find for you ! good work ^^
Your SOKOL 403 has similar, capacitively coupled IF tanks. The SOKOL has 5.6pF intercoupling caps, but it has larger (510pF) caps in the IF tanks too. 2.7pF coupling is a good match for the 160pF IF tanks in this radio. The schematic is obviously wrong, that is a pair of capacitively coupled IF tanks, not a transformer. There is no inductive coupling between the two coils, they are totally shielded from each other by the aluminum can and the pot tuning cores that surround the coils.
That schematic is deceiving, it is not a transformer. There is not any inductive coupling. They are just tuned LC filter circuits coupled with a very low value capacitor. The coupling cap may even be .21pf as the silver band could be a .01 multiplier.
@@danmackintosh6325 The older I get the easier it becomes to listen to my gut. Partly because it has more to say for itself and partly because it appears to be the only part of me that isn't shrinking. ;~)
26:00 I like those CONELRAD markers on the flip side of the dial with a separate pointer. Almost makes you wish for a nuclear war just to try them out.
Do you use a signal tracer to isolate what is causing the motorboat sounds since its clear its not the if coils that were recapped? Was this radio ever fixed?
It's capacitively coupled NOT inductively coupled ..... The best way to determine the capacitor size would be to measure the inductance of the coil with the slug out (minimum inductance) and then turn the slug in to get maximum and then use whatever is halfway. Then just plug that inductance and 455Khz into a resonance calculator and you'll have your capacitance. Pick a value that is close to the calc (You hardly ever get a value that lands exactly on a common capacitance) and then use the slug to peak it. The coupling capacitor is an entirely different story because you need to find the "critical coupling" value (Keeps the passband flat with no dips and peaks) and that's hard to do without a sweep generator and a scope or a spectrum analyzer so you can see the passband
I've done a lot of homrbrewing and prototying of superhet cw transceivers. I've replaced commercial Chebychev bandpass filters with one I built on a daughter board- which are basically what you have there with your two coupled IF cans.. and in my case- the capacitor coupling the two filter sections was SMALL shango.. always, always on the order of 2.7 to 3.3pf. Never more than 4.7.. and even that really broadens up the filter peak and flattens it
Are you sure your IF stage isn't oscillating? That tuning sounds like a regen that's been driven beyond the highest gain. Or a Hallicrafters S-120 with the "BFO" turned up. Cool circuit!
in tube radios ( hammarlund) the mica caps are leaves open to the atmosphere, and they routinely are found bad.. with a totally dead stage. removing them and installing outboard sealed mica caps is the cure. I have never tried compressing the coil in those much larger if cans.. this seems like a bad solder job.
Didn't you have a similar problem on an Arvin set about a year ago? On both sets I would change the resistors on the feedback line and see what happens. You don't need to take the Philco apart for this as you can chop the resistors out and solder to the leads. Good Luck.... Unless these two sets are for use in weak areas?
Greetings: Since the core threads are very visible, can removing the core itself permit measuring the existing capacitor value permitting the closest SMT cap (size appropriate) to be placed in position and attached (or under pressure) as the original was before restoring the core? Gives you a place for a good capacitor. My best educated guess is that the 2.6pf cap is to couple the two tank circuits together passing the rf since the cans themselves cannot couple the inductors. I'm sure you will learn that other resonant tank circuits using similar cans have a distinct method of non-inductive coupling of circuits. I want to be sure not to forget to congratulate you for thinking of the additive affect of using a second cap to put the values in range of the component tester when looking for the value of the 2.6pf cap. AVC: can you compare the working of the two radio's AVC circuits to determine if they are different (even using the signal gen to establish the rf levels that create relevant levels).
How about if the original Micah sheep was turned in the other direction where the black mark was not the point of contact maybe that would have done the trick
