Hallicrafters SX-110

[electra225]

I fired up my big Hallicrafters radio this afternoon. I brought it up on the Variac just in case. It seems to be as good as it ever way. I have a 20' hank antenna on it, stretched along the shelving in the shop. Seems to work fine like that. The signal is strong enough to almost peg the meter, so that is good. One of these evenings, I am going to see what I can find on radio around here after dark.

[electra225]

I was listening to 550 AM this afternoon, when the audio just quit. Nothing on the dial under 950 Khz. Above that, all is well. What do you reckon happened?

[TC Chris]

Oscillator tube? Seems to me those usually get picky at high frequencies, not low. Or maybe a cap in the oscillator section? Or lastly, the grounding fingers on the tuning cap?

Chris Campbell

[electra225]

I have a spare oscillator tube I believe I'll try first. You'd think a cap wouldn't go all at once. I used to have trouble getting oscillators to work on the low end of the dial in Missouri where the signal was not as strong as here. Shortwave bands work okay, the upper end of the broadcast band works okay. Just the low end of the broadcast band is affected. All good suggestions, Chris, and I thank you.

[electra225]

LED lights killed my Hallicrafters.

[TC Chris]

You mean they wiped out the lower frequencies? With noise?

Technology can have unintended consequences. I do like the low current draw and durability of the LED lights, but their supposed longevity seems to be WAY overrated. I replaced one at home two days ago. It started flickering badly. The earlier generation power saver, the compact fluorescents, had similar longevity claims and similar premature failure rates, in my experience. Incandescents are either/or, and usually seem to have long lives.

Chris Campbell

[electra225]

No, no noise. Just no reception. The orientation of my "antenna" system caused the LED lights over the bench to kill the lower frequencies of the Hallicrafters radio. Rex posted a topic where his entire radio was dead due to LED lighting. The antenna I was using was a 20' hank of hookup wire, run along the peghooks for the shelves then connected to a 25' extension cord draped on the peghooks on another wall. I was tinkering with the radio, so I turned off the bench lights so I could see if all the tubes were lit. When the lights went off, the radio came on. I had never seen that happen before.

[TC Chris]

So could you use some well-shielded coax to get an antenna beyond the lights' reach?

Chris Campbell

[electra225]

No, I could use some incandescent bulbs in the light fixtures over the bench. LED's and I are on the warpath in the shop. They are great for the house, not so much in the shop.

[electra225]

I learned something else interesting, quite by accident concerning this radio. This Hallicrafters radio has switchable and adjustable AVC. Most home broadcast radios have AVC, but it is built in the circuit and is not maneuverable by the user of the radio. I had this radio on the bench trying to find what ailed it, when my wife came to the shop door, needing my assistance. The radio was set to a low frequency in a "dead" part of the dial. The AVC was on. I shut off the LED bench lights. The radio came to life. I turned the lights back on, radio was dead again. I turned the AVC off and the radio played, but weakly. Turned the lights off again, with the AVC still off, and it blasted me out of the room. Something in the LED lights and the AVC circuit in this radio interact with each other to kill the radio below about 750 Khz. The radio actually works better, with better volume and sensitivity with the AVC off.

[TC Chris]

The radio actually works better, with better volume and sensitivity with the AVC off.

Thinking out loud, which is always a dangerous undertaking... but isn't AVC just a sort of RF-level feedback to reduce gain on strong stations? So turning it off leaves the RF gain floored.

It would be interesting to see what sort of frequency spectrum those LED lights are generating. And whether they are "broadcasting" it or sending back on the AC power line.

Chris Campbell

[electra225]

The old TRF radios didn't have AVC. They also did not have a local oscillator. Most of them had the volume control in the front end of the radio. Instead of limiting the signal to the audio, that arrangement would limit the amount of RF gain. All there was to a TRF radio was five or six stages of RF amplification, fed to a detector, then on to the audio stages. I haven't had my old Temple TRF radio fired up yet, but my guess is the LED lights won't bother it one bit. My theory on why the LED lights kill the Halli is that something in the brilliance control in the lights, in conjunction with the switchable AVC circuit in the radio is killing the low end of the broadcast band. I don't think the lights are broadcasting a signal, per se, but they are generating a signal that mixes with something in the radio which cancels out the low end of the broadcast band. This does not happen with radios with built-in antannae. My next test is to move the hank antenna for the Halli down closer to the floor to see if that makes a difference. The antenna wire may be too close to the lights.

[hermitcrab]

LED's are not the only enemy to AM reception ... My transoceanic was useless anywhere in the house ... turning off LED's and flat screen TV did nothing... until I went around unplugging wall warts while the radio was on...and lo and behold , I unplugged the wall wort for my internet modem and voila... all noise ceased and reception was great ... those switch mode power supplies are awful for this problem...

[William]

The wall wart on my walk-about house phone messes up the big Philco as does the DC motor in my Speed Queen washer. As the motor pulses first one way and then the other you can hear that in the radio.

Bill

[electra225]

As you can tell by reading this topic, I've been having a series of issues with this radio. The first step is to remove the chassis from the cabinet then check all the voltages and make sure it's okay electrically. The purpose of this post is to discuss the rather different alignment instructions that are not typical of a broadcast band receiver.

Doc Radio was good enough to link the schematic for this set. I'll include that down further. Right now, let's talk a bit about some of the alignment instructions that I'm not sure about. Let me include here that I recapped this set when I got it. That may be part of the trouble. I shotgun caps, so I'm sure that happened in this case. The book plainly states that if components are changed in the RF or IF stages (I'm sure they were) then alignment may be necessary.

The IF in this set is 465 khz. In the RF alignment instructions, they don't recommend doing an RF alignment without using laboratory-grade signal generators. If normal service generators are used, they want you to skip to Step 3, which is a regular old IF alignment as far as I can see, with one caveat. They want you to set the signal generator to the "crystal frequency". The instructions are not specific, but I'm guessing, if I read right, that you determine the crystal frequency by setting the generator initially to the IF frequency, then adjusting the generator above or below the IF then find the maximum deflection on the output meter. Then you use that frequency to perform the balance of the alignment procedures. Am I on the right track?

Then, for the oscillator and mixer alignment, they want you to use an RTMA dummy antenna. What the heck is that? The book shows a 20uh choke, fed by a 200 pico farad cap. Then there is a 400 pico farad cap in series with a 400 ohm resistor across the choke. It does not give a generator frequency, but I assume you use the crystal frequency, right? Then there are eight steps of adjustments to oscillator and mixer trimmers. I need to understand this, since there is weak performance at the lower end of the dial, indicating to me the possiblility of oscillator misalignment. I've never aligned a boat anchor with so many opportunities for making a mistake. Maybe we can toss this around a bit so I'll have a better understanding.

[Dr. Radio]

Greg,

I have not had a chance to really analyze the alignment instructions given by Hallicrafters. That may require a special "thinking fluid" found inside of a brown glass bottle....

I stumbled upon this, I realize it is a different model, but this might help. It's a bit long, I only jumped around in the video....

https://youtu.be/HEGtXekNB5M

[TC Chris]

They want you to set the signal generator to the "crystal frequency". The instructions are not specific, but I'm guessing, if I read right, that you determine the crystal frequency by setting the generator initially to the IF frequency, then adjusting the generator above or below the IF then find the maximum deflection on the output meter. Then you use that frequency to perform the balance of the alignment procedures. Am I on the right track?

Then, for the oscillator and mixer alignment, they want you to use an RTMA dummy antenna. What the heck is that?

I think you're right about the "crystal frequency" being one set by the specific crystal used, close to 465 KHz. I can't find the manual that was posted (where is it?) so I'm guessing that the oscillator is crystal controlled for stability.

And the RTMA dummy was probably a standard fake antenna load that everybody knew back then. RTMA was the trade organization, wasn't it? Or probably trade and standards.

Chris Campbell

[electra225]

Is it mandatory that I use that exact dummy antenna? And, do I use the crystal frequency for the oscillator and mixer alignment?

[TC Chris]

Where is that manual with the schematic?

[Dr. Radio]

Where is that manual with the schematic?

Morning Chris,

I originally posted a link in this thread: viewtopic.php?f=6&t=1421&start=10


Here's the direct link to keep things simple:

http://www.njarc.org/manuals/Hallicraft ... ctions.pdf

I offered this video to Greg in the thought it might provide some clarity (even though it is a different model):

https://youtu.be/HEGtXekNB5M