Always great to see another Hally get back on line. You must have experience teaching because your videos are well constructed to instruct. You are the first restorer I have seen to address the reality that houses are not always correctly wired. When I move into a house I test every outlet fixture to ensure proper wiring, but you have taken the extra measure. Blessings, Albert.
31May20/0408UTC. Sir, thank you for the video. A radio or any Electronic device never dies, especially, the analogs. Of course, it can be killed. That’s different story, altogether. An AC/DC set was cheaper to manufacture plus lighter. The rectifier normally is only SOLID STATE device, being Selenium. Once the filter Capacitor (20mfd/220V )laminations get shorted or dry; the Selenium rectifier gives out nasty odor and dies ! The Se is replaced with Si bridge. Analogs doesn’t die. Recap and reuse. 73s
With how often I've found miswired outlets I feel the real safety upgrade with the "floating" chassis transformerless stuff is appropriate short proof X/Y type safety capacitors in the across the line and line to chassis positions. At that point you're approaching modern standards.
The "BFO" circuit in the S-38 through the S-120 is an interesting circuit indeed. It's also different between the '38 and the '120, as we shall see. In the S-38 series, this circuit consisted of a length of hookup wire laid along the grid and plate leads of the IF tube, but not connected to anything at this end. The other end of this wire was connected to one side of a SPDT switch, with its center terminal connected to ground. The far end of the switch is connected to the AVC line of the receiver. The AM position of this switch has the wire leading to the IF stage grounded. Flipping the switch to the CW position grounds the AVC line, causing the receiver to operate at maximum gain. It also causes the wire laid across the IF stage to float. Now, this wire acts as a gimmick capacitor, coupling the plate and grid of the IF tube, causing it to oscillate. Since the value of this gimmick capacitor coupling is very small, less than 1pF (or μμF if you prefer), its effect on the tuning of the stage is quite small. The S-120 is a different animal. Like the S-38, the IF stage is made to oscillate, but how it does this is actually superior IMNSHO to the gimmick method discussed previously. In an IF tube, both the screen and suppressor grids act as electrostatic shields between the control grid and plate. This time the switch of the BFO control connects the AVC line to ground, but only if the BFO is turned on. The bottom of the control is also grounded. The wiper is tied to the suppressor grid of the IF tube, so when the BFO is off, the suppressor is grounded. As the control is advanced, the RF decoupling from the suppressor is removed. As this happens, the capacitive coupling between the the plate and control grid is increased. In a way it's like the gimmick in the S-38, except there's a mechanical coupling to move the wire towards or away from the tube socket. In practice, the BFO control of the S-120 behaves like that of the regen control of a regenerative receiver. Beyond the point of maximum gain, the stage breaks into oscillation, and CW reception is possible. These two methods of oscillating IF CW reception for the S-38 and S-120 are covered in US patent numbers 2,556,993, and 3,107,333, respectively. Another feature about the S-120 that I find an improvement, is the change from air core coils in the former, to individual slug tuned coils in the latter. The Lafayette HE-40 is practically the same as the The S-120, except for the addition of an S meter, a tone (high cut) switch, and ANL. The latter looks laughingly easy to implement, it ties one of the diode plates of the 12AV6 to the control grid of the output tube.
@@MIKROWAVE1 I imagine that the S-120 would have been more capable of having a genuine BFO, since there was enough chassis real estate, and they used a selenium rectifier, allowing for the capability to light another tube heater. However, they were building to a price point. A pot with a switch and some wire were probably cheaper than a tube socket, tube, coil, other passives, and the labor to put it all together. In the end, the regen approach was the most clever IMNSHO. :-)
Thanks for the walkthrough on the 120. Something on my to-do list is to start getting my ham license, just have to figure out how to do that without being able to put up an antenna. Details, details :D Hope you are doing ok, Cheers
Thanks for the video. I have my father's old Knight Star Roamer and was thinking of getting that up and running. I know it will need more than a recap and replacing the selenium rectifier with a silicon diode. The Dial cord slips and the band selector is stuck and I'm afraid it would require disassembly of the fiberboard rotary switch stack to properly clean and lube the contacts or worse switch replacement. As of now I just cleaned the outside and set in my shack as a display memorial..
A few months ago I replaced all the caps (Hayseed Hamfest), power cord (polarized), and selenium rectifier (diode) in my Hallicrafters S-120. I had two extra parts radios, and picked out the best tubes, speaker, and cabinet pieces. I was also in touch with pi-duino (see below) for advice. When I was all done (B4 the alignment), I had a hum in Stand-By. This drove me so nuts that I walked away from the project for a while. I was so relieved to watch your video all the way thru, and hear you say that one cannot get the hum out of any of these w/o modifications. There is an odd looking part in the parts radio, called a couplate in the schematic. It is attached to several other components, like a spider. I thought about swapping that into my recapped radio, but now I'm not even going to mess with it. I'm going to do the alignment on it soon, and call it a day. Thanks. 73 Paul AA1SU
That was a too clever approach at a multi-component Module. Basically it is a bunch of passive components like resistors and capacitors connected internally, in a coated assembly with wire leads. It saved cost on things like terminal strips.
@@vtradio I don't think it will help. The main culprit is the way they ran the linecord to the on off volume control which was a very high impedance pot and audio wiring section. It is just tough to isolate the two. Almost everything I tried helped, including rerouting a brand new cord so that it came in at a better angle, shielding the audio, changing out the pot to a 200K and so on. But there was no silver bullet.
Would it be possible to rebuild that radio using Raytheon Wire-Ended vacuum tubes and generally make it work on between 12-30V instead of working on mains voltage that could very easily send you to an early grave and while we are at it could we not use 455KHZ Murata crystal filters instead of IFTs.
enjoyed video pulled mine out of closet picks up am but not any short wave at this time. Will continue to work on mine, do you work on any for us non qualified beginners. Thank you, Bill Morkes Pensacola fl
Well first you have to believe in Mica Oxidation Evaporation Disease. I am sure it is real. I just have not seen it. Just a noisy spring week here with storms moving through.
I always use Hayseed. They have other great kits as well. It's worth buying a kit! Besides the *1N4007,* add a *100Ω* *10W* resistor in-line. At 20:00 I hear what sounds like a resistor or CAP that is arcing! Here are some MODs listed at my Web site for Hallicrafters S-120 & Realistic DX-160: elecurls.tripod.com/ph.htm
One of the big differences between selenium rectifiers and modern silicon diodes like the 1N400x series is the on series resistance - selenium rectifiers behave more like tube rectifiers in that they generally add a few hundred ohms when conducting. Silicon diodes, once past the conducting voltage, add very little resistance and result in B+ voltages being as much as 30-50v higher than the original tube rectifiers. As you say, adding a few hundred ohm power resistor compensates for that, and also reduces the in-rush current to the filter caps when the receiver is first turned on. Definitely recommended if you swap silicon rectifiers in place of tube or selenium ones.
K1OIK- I never recap, if it works I don't "fix" it. You clean the vacuum tubes with a vacuum cleaner. I like to use mine in the bathtub. The S-120 is a highly dangerous. You get more than a tickle.
Burt, I like to recap a radio for both safety and the experience. I have a S-38D that shocks me every time I plug it in wrong, not just in the bathtub either. I don't plug it in anymore. On the other hand, that Hallicrafters SX-110 I sold you worked great just the way it was when I found it. All I did was change the dial bulbs, and maybe a tube. 73 Paul AA1SU
