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

    Well, the post office delivered my Hayseed Hamfest replacement capacitor can to an 'Agent' ... somewhere.

    I am going to attempt to restuff the existing can for the time being. I think I have enough information (schematic and pictures) to figure out where each goes - it looks like the 30uF and one of the 10uF are in parallel between the IF Transformer and pin 4 of the audio output tube (VK6-GT). The other 10uF looks to connect to the coils on the mixer.

    I'll take a look at the pictures and determine which prong on the can is going to ground and then solder it up.

    Thanks for listening as I walk myself thru this.
  2. K9STH

    K9STH Ham Member QRZ Page

    The entire outside of the can should be the "ground"! Usually, there are 3-tabs, sometimes 4-tabs, that go through holes in the chassis and then are "bent" to hold the can in place. Often, these tabs are soldered to the chassis.

    Glen, K9STH
  3. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    The post office has located my capacitor and swears it will be in my hands today. In the meantime, I started to clean the radio chassis surface and decided to do something a little different. I'm not sure how some of the radio purists will react but I like it, and it's my radio after all. So without further ado, and with full knowledge that I may be beaten about the head for doing this, I present to you the 'jeweled chassis' of my S-85. (It's not complete yet - there are still some nooks and cranny's that I have to get into - but this is what I am going for:

  4. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    Good news and bad news.

    Good news - after re-assembly the unit powers up, the lights turn on and the 6K6-GT and 5Y3-GT tubes glow. The bad news - there is a pronounced hum coming from the speaker regardless of the volume setting or any other setting for that matter. I hear it on the speaker and on the headphones.

    Going to begin my google search and looking for suggestions here on what to check first.

  5. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    I found a cap that goes between the Audio amplifier tube and the audio output tube that was discharging DC from about 350 volts to 70 volts and staying there. I clipped on lead and the hum went away - I'm going to replace that cap and see if the hum returns - it's possible I put it on the wrong pin of the tube.
    KA0HCP likes this.
  6. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    Replaced the capacitor and hum is gone. That was a new one - wonder if I damaged it when soldering it? In any case, once my signal generator and O-scope arrive this week I'll take a crack at aligning it. It receives some broadcast stations but they seem to be way off on the dial.
  7. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    OK - the time has come - I have started the alignment procedure - but I have a question or two.

    I am starting with the IF alignment with the radio out of the chasis
    • I have setup the initial configuration on the radio as follows:
      • Band Selector at 1 MHz (MC)
      • Sensitivity and Volume: Max
      • AM-CW switch: AM
      • Noise Limiter and AVC: OFF
      • Rec-Standby: REC
      • Tone: High
      • Bandspread: Fully Clockwise
    • I have the signal generator set to 455 KHz (KC), AM Modulation, .5V Amplitude
      • Ground is connected to Chassis
      • High side is connected a .02 uF capacitor then to Pin 8 of the 6SA7 converter tube (v2)
    • I have the Oscillator connected to the speaker leads
    When I turn the radio on (Tone to High), I see a sine wave on the oscilloscope. The instructions say to adjust for maximum output by adjusting the top and bottom slugs of T1, T2 and T3. Here are my questions:

    1. Regardless of the adjustment I make to the top of the slugs, the amplitude of the sine wave does not change.
    2. I do not see any adjustment on the bottom of the slugs - there is a hole but I don't see an adjustment slot in there when looking with a flashlight.
    I'm not sure if this indicates a problem with me or with the radio :)

    Any advice is appreciated.

  8. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    Hmmm - to add insult to injury, I think one of the slugs 'broke' - it looks like the adjustment slot is no longer aligned with the top hole - investigating whether the cover can be removed to effect repairs.

    To be specific - it is the IF Transformer for the detector stage (50C242 / 119-6-46) - maybe I can find one at the HamFest tomorrow?
    Last edited: Mar 10, 2018
  9. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    So, as I look at this more closely - the Oscilloscope is actually not seeing a signal at all - there was noise that I thought was the signal, but if I remove the signal generator entirely the o-scope does not change. If I connect the sig-gen directly to the o-scope i get a clean sine wave at the correct amplitude and frequency.

    Looking at the bottom of the pin connector for V2, the key does not appear to be in the same position as in the manual. However there are numbers on the bottom indicating which lead is for which pin - so I am still connecting it to pin 8 on the bottom of the connector based on that numbering.

    EPIPHANY: The chart I have on the wall is revision 92E1097-D - the chart in my manual is 92E1097-C (and this one has the key in the right spot)

    I tested the voltages of the tube and they appear to match the manual within spec.

    So if I have an octal tube - is pin 1 always the first pin to the LEFT of the key (looking at the pins) and pin 8 is always the first pin to the RIGHT of the key?

    When looking at the diagram my measurements of expected voltages appear to follow that logic.

    Additionally - if I am inputting 1v into the ping for Grid 3 on the 6SA7 - should I expect some amplification on the source signal?

    Thanks again!
  10. K9STH

    K9STH Ham Member QRZ Page

    You can get a fairly close alignment just by using your ears!

    With the r.f. gain fully clockwise, turn on the BFO and then adjust the frequency, on the signal generator (without any modulation), so that there is a tone of a comfortable frequency that you want to listen. Reduce the signal generator output until you can still hear the tone but there also is a fair amount of noise. Then, carefully adjust the tuning slugs so that the tone volume increases and the noise level decreases. If the tone gets full quieting, then reduce the signal generator level so that the noise level increases. Keep aligning the unit until none of the alignment adjustments improves this signal to noise ratio.

    You can also use the modulated signal from the signal generator with the AVC and BFO turned off to align. However, I find that using the un-modulated signal with the BFO works better.

    It is VERY easy to get caught up with in the "details" when doing alignments, etc. With experience, you will find that there are usually easier, often better, methods to use when working on the equipment. Following the manufacturer's methods will usually produce satisfactory results. However, sometimes, there are errors in the published procedures as well as the procedures often being "drawn out". In addition, with most equipment, the actual alignment has already been done, at the factory, and the real need is to just "touch up" that alignment due to replacing tubes or other components.

    Glen, K9STH

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