Adjusting Hallicrafters SX-85 Main Dial and Band Spread Position

Discussion in '"Boat Anchor" & Classic Equipment' started by KD2NOM, Feb 3, 2018.

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  1. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    Thanks Glen.

    I am not able to hear a tone from the radio - just noise. I've tried running the tone generator straight to the antenna inputs as well as the IF alignment locations with no joy.

    I'm wondering if I messed something up during the capacitor replacement - maybe soldered a capacitor to the wrong terminal somewhere.

    The radio is overall very quiet and then as I am turning the main tuner gets very loud - but not with anything that sounds like a broadcast.

    I'm going thru now measuring each tube to make sure the out put is what is expected. I think I'll have to go thru the schematic and make sure everything is where it's supposed to be.

  2. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    Think I'm getting a bit closer - I can actually hear the tone - it's just off frequency quite a bit - I need to find a non-conductive tool so I can adjust those slugs / coils thru the case
  3. KD2NOM

    KD2NOM XML Subscriber QRZ Page

  4. K9STH

    K9STH Ham Member QRZ Page

    What are you using for a signal generator?

    Do you have a counter to verify the frequency out of the signal generator?

    Glen, K9STH
  5. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    I have a FeelTech Dual Channel Function / Arbitrary Waveform Generator (60MHz) - I verify it's output against a Tektronix TDS210 oscilloscope. I am using a sine wave at frequency with 1v amplitude and no offset or phase shifting. I'm not sure what I should be hearing out of the speaker. For example, I set the frequency generator for 28MHz at 1V and attached the high side to antenna post A1 and the ground to Antenna post A2. I turned the RF gain and the sensitivity all the way up, set the band select to full clock wise and the main dial to 28 MHz. I hear 'noise' beginning around 26MHz up to about 30MHz on the main dial - but no definitive tone. Perhaps I am not setting up the tone generator properly? Should I actually hear a tone out of the speakers?

    I also pulled out the T3 IF Transformer and took the case off - the top slug adjustment 'slot' broke up a bit - I found a source for a replacement at the Hamfest today and hopefully will have one here in a couple of days. So until that is back in place there will be no more testing.

    BTW Glen - I really appreciate you Elmer-ing me on this - I am trying to do a lot of Googling and research before I post here.
  6. K9STH

    K9STH Ham Member QRZ Page

    Turn on the BFO. That is, put the AM / CW switch in the "CW" position. Make sure the bandspread dial is set where the HIGHEST frequency is shown.

    Do you actually mean 1-volt output from the generator? If so, that is WAY too high an output. You need to reduce that to no more than 0.1-volt at most. Now, if you really mean 1-microvolt, then that is way too low an output. If you mean 1-microvolt, increase the signal to 1000-microvolts.

    Set the generator frequency at 28.0 MHz. Then, VERY slowly tune the main tuning knob around the 28.0 MHz indication on the dial. You may have to go from a much lower frequency to a much higher frequency because the calibration can be way off. If the receiver is actually receiving, you should suddenly hear a loud tone.

    In fact, if you "tune around", you will actually get 2-signals and those will actually be 910 kHz apart. The lower frequency signal is actually the "image" which is caused by the 455 kHz i.f. On the higher frequency bands the injection (tunable) signal is on the "low side" which means the desired heterodyne of 455 kHz is produced by the actual signal being higher in frequency. However, the higher the received frequency the stronger the image is going to be.

    If you get a signal, reduce the signal level so that the receiver is not being overloaded. Then, do the frequency calibration for the band. You will have to go from the high side to the low side quite a few times before getting the calibration close. Frankly, even when you get the "end points" (high and low) frequency "spot on", there is a very good chance that in between those points, the calibration can be "off" a fair amount. This is the "nature of the beast" and you will just have to live with it! You can use an external crystal calibrator so that the actual frequency is known even if the dial doesn't show that frequency exactly.

    If you do not get any signal, then first try a frequency much lower in the band and see if you can receive that frequency. If no luck, then go to another band and try frequencies on those bands.

    To make sure the i.f. is really working, set the signal generator to 455 kHz inject this signal at Pin-4 of V-3. You may have to tune the "Pitch" control to hear the signal.

    Glen, K9STH
  7. KD2NOM

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    Things are beginning to make more sense. I was able to retune the IF Transformers after re-assembling T3 and resoldering it's connections - I made a non-conductive adjusting tool out of a wooden dowel while I wait for my proper tools to arrive.

    I had the power clearly set to high and once I brought it down to .1v and was able to catch the tone - I was able to zero beat the pitch control as well.

    I then set the frequency generator to 28MHz, set the BFO on and found the signal a little below 28MGz (probably closer to 27.5 ). My dowel won't work for trimming the capacitors for the osc., mixer and antenna so I'll have to figure out something else for that.

    The signal generator seems to get a little dicey at very low amplitude - when connected directly to the o-scope (no radio) the traces are pretty jumpy.

    The part that was confusing me is that I expected to see an output on the o-scope of a peak that I was going to tune to - but I don't get that at all - I get a jumbled mess on my screen - I'm not sure if I am measuring at the wrong spot (the leads to the speaker), if the signal generator is just not up to the task, or the o-scope is not setup right - so many things to learn and test.
  8. K9STH

    K9STH Ham Member QRZ Page

    Keep tuning higher in frequency than around 27.5 MHz and see if you get another signal around 28.5 MHz. Also, tune down to about 26.5 MHz to see if you get a signal. If there is a signal around 26.5 MHz then the one at 27.5 MHz will be the actual signal and the 26.5 MHz (actually would be 26.6 MHz) will be the image. If you get a signal around 28.5 MHz (actually would be 28.4 MHz) then that will be the actual signal and the 27.5 MHz signal will be the image.

    Images are a definite problem with single conversion receivers like the S-85 and the higher the frequency the stronger the image is going to be.

    You don't want to calibrate mistakenly on an image because that will throw off the other end point and, even more, the calibration in between the end points. That calibration can be bad enough without having the end points wrong but when an image is thought to be the true signal, the in between calibration is going to be even worse.

    If you really want to use an oscilloscope as a signal indicator, then you really need to look before the signal is detected (converted to audio). Pin-8 of V-4 or Pin-5 of V-7 would be a good place to start. However, do NOT adjust T-3 when the oscilloscope is connected to either of those locations.

    Glen, K9STH
  9. WB1E

    WB1E Ham Member QRZ Page

    If Remember correctly, the slugs change the lower frequency and gain, and the variable caps do the same on the high end. One thing for sure, on these Halicrafters receivers, you will have to go back and repeat the same band for alignment at least 3 times, I have spare slugs! I did split one. Glen is doing you perfect! I use a deflecting needle voltmeter to give me the 5oomV (AC) output indication. If you hear WWV, use it as a frequency reference. But the top & bottom may be dead on, but not so much the middle. I have 2 SX99 receivers, and they are very quiet, but sound good with a decent signal. They will be going to the Belton hamfest next month.

    Good luck,
    Last edited: Mar 13, 2018
  10. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    Glen - pin 8 of V-4 gives me a clean sine wave on my scope and I am able to visually increase the amplitude - I have steered clear of adjusting T-3 when connected there.

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