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Old 4th Aug 2020, 8:27 pm   #121
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Default Re: Another Hallicrafters Sky Champion S20.

The counters readings did change as I changed the dial. I started at the 1440khz station I tuned to.

Turning the sets dial toward 550 kHz did drop the signal counters value, but at a point around 900 it dropped to illogically low and by 800 Khz or so on the dial the count was nothing (as if it dropped off).

I'll make up a table of what I have found and post it.

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Originally Posted by Station X View Post
The IF Transformer trimmers have absolutely nothing to do with the tuning of the local oscillator. Leave them alone for now.

Does the counter's reading change as you tune the receiver?

As you tune across the AM band from 550kHz to 1500kHz you should see the local oscillator's frequency change as you tune the receiver. Pause tuning for a couple of seconds every turn or so of the tuning know to let the counter catch up.

With the tuning set to 550kHz the counter should read 1005kHz.
With the tuning set to 1500kHz the counter should read 1955kHz.

Your counter's reading of 1443.82kHz?? would be correct if the receiver was tuned to 988.82kHz which is around 300 metres.

Try to produce a table showing dial settings and counter readings. There should be a constant difference of 455kHz across the band.
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Old 4th Aug 2020, 8:35 pm   #122
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Default Re: Another Hallicrafters Sky Champion S20.

Not quite the results I expected.

I first made sure the sig gen was at 455, then connected counter to the mixer as I did before. Then clipped the sig gen to the mixer cap. The radio station immediately stopped and the counter read basically zero. :-(


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Originally Posted by ms660 View Post
The counter looks to be capacitively connected to g1 of the mixer...with the counter still connected as in the photo connect the sig gen to the actual top cap of the mixer and tune the sig gen to 455kHz.

Lawrence.
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Old 4th Aug 2020, 8:52 pm   #123
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Default Re: Another Hallicrafters Sky Champion S20.

Pull out the local oscillator valve, BFO off, AVC off, RF gain to max. no antenna input, tune the receiver to the top end of the BC band, connect the signal generator to g1 (top cap) of the mixer, couple the frequency counter to g1, connect a 'scope via an X10 probe to g1, then with its internal modulation switched off set the signal generator to give a 455kHz display on the frequency counter and adjust the output of the signal generator for 100mV peak to peak on g1 (with the 'scopes X, Y and time/div variables set to cal.)

That should tell us that a suitable signal is being fed into the mixer for testing purposes when we see a photo or two of the said and can verify the frequency and amplitude of the test signal.

Then take it from there.

Lawrence.

Last edited by ms660; 4th Aug 2020 at 9:02 pm.
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Old 4th Aug 2020, 8:56 pm   #124
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Default Re: Another Hallicrafters Sky Champion S20.

- S20 tuned to 1440 Khz - Frequency Counter at about 1585 (fluctuating from 1450 or so)

- S20 tuned to 1350 Khz - Frequency Counter at about 1910 (fluctuating around that value)

- S20 tuned to 1340 Khz - Frequency Counter at about 1272 (fluctuating around that value - and starting to drop!)

- S20 tuned to 1300 Khz - Frequency Counter at about 450 (fluctuating around that value - and starting to drop even more!)



Quote:
Originally Posted by Station X View Post
The IF Transformer trimmers have absolutely nothing to do with the tuning of the local oscillator. Leave them alone for now.

Does the counter's reading change as you tune the receiver?

As you tune across the AM band from 550kHz to 1500kHz you should see the local oscillator's frequency change as you tune the receiver. Pause tuning for a couple of seconds every turn or so of the tuning know to let the counter catch up.

With the tuning set to 550kHz the counter should read 1005kHz.
With the tuning set to 1500kHz the counter should read 1955kHz.

Your counter's reading of 1443.82kHz?? would be correct if the receiver was tuned to 988.82kHz which is around 300 metres.

Try to produce a table showing dial settings and counter readings. There should be a constant difference of 455kHz across the band.
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Old 4th Aug 2020, 8:59 pm   #125
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Default Re: Another Hallicrafters Sky Champion S20.

The final pix (and drop to ZERO).

- S20 tuned just under 11000 Khz - Frequency Counter at about 110 (fluctuating around that value - and starting to drop!)

- S20 tuned a little more down from 1100 Khz - Frequency Counter at about 5.7 (fluctuating around that value - and starting to drop!)
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Old 4th Aug 2020, 9:01 pm   #126
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Default Re: Another Hallicrafters Sky Champion S20.

- S20 tuned to 1600 Khz - Frequency Counter at about 2162 (?)

I am convinced the set is possessed.
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Old 4th Aug 2020, 9:48 pm   #127
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Default Re: Another Hallicrafters Sky Champion S20.

Sorry, but your readings make no sense at all.

You'd best try Lawrence's test.
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Old 4th Aug 2020, 10:10 pm   #128
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Default Re: Another Hallicrafters Sky Champion S20.

I think this is what you wanted: LO valve is pulled out, 10x probe on scope, freq counter and sig gen (MODULATION OFF) both set at 455Khz, all three devices on 6L7 (mixer) grid cap, set BFO & AVC off, RF gain to MAX, set tuned for max (beyond 1800 Khz on dial). And I think I had the scope set to show wave.

I did not hear anything out of the set (not sure if I should have been able to).

Quote:
Originally Posted by ms660 View Post
Pull out the local oscillator valve, BFO off, AVC off, RF gain to max. no antenna input, tune the receiver to the top end of the BC band, connect the signal generator to g1 (top cap) of the mixer, couple the frequency counter to g1, connect a 'scope via an X10 probe to g1, then with its internal modulation switched off set the signal generator to give a 455kHz display on the frequency counter and adjust the output of the signal generator for 100mV peak to peak on g1 (with the 'scopes X, Y and time/div variables set to cal.)

That should tell us that a suitable signal is being fed into the mixer for testing purposes when we see a photo or two of the said and can verify the frequency and amplitude of the test signal.

Then take it from there.

Lawrence.
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Old 4th Aug 2020, 10:11 pm   #129
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Default Re: Another Hallicrafters Sky Champion S20.

Scope setting up-close (sorry its an OLD bench scope!).
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Old 4th Aug 2020, 10:15 pm   #130
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Default Re: Another Hallicrafters Sky Champion S20.

The set's behavior is quite bewildering to me as well.


Quote:
Originally Posted by Station X View Post
Sorry, but your readings make no sense at all.

You'd best try Lawrence's test.
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Old 4th Aug 2020, 10:16 pm   #131
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Default Re: Another Hallicrafters Sky Champion S20.

What's the SEC/DIV switch set to?

Is the variable (VAR) control in its CALibrate position, generally fully clockwise?
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Old 4th Aug 2020, 10:30 pm   #132
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Default Re: Another Hallicrafters Sky Champion S20.

** CORRECTION **

Good catch on the Cal - I didn't set it on the dent position (full CAL on both settings).

I reset it up and retook pix:

- SEC/DIV: 0.1us
- VOLTS/DIV: 50m (looking at the 10x probe indicator)

Last pic is closeup of the scope settings.


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What's the SEC/DIV switch set to?

Is the variable (VAR) control in its CALibrate position, generally fully clockwise?
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Old 4th Aug 2020, 10:46 pm   #133
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Default Re: Another Hallicrafters Sky Champion S20.

Can we have a close up showing the settings of the signal generator please.
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Old 4th Aug 2020, 11:09 pm   #134
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Default Re: Another Hallicrafters Sky Champion S20.

As requested

I would use the Hickok 288X I have, but this one is as accurate and much simpler to use. This work great for simple SG uses.

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Can we have a close up showing the settings of the signal generator please.
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Old 4th Aug 2020, 11:24 pm   #135
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Default Re: Another Hallicrafters Sky Champion S20.

That looks OK to me assuming Band B is selected.
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Old 4th Aug 2020, 11:59 pm   #136
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Default Re: Another Hallicrafters Sky Champion S20.

It IS band B - the IG102 is pretty slick in how simple it is. You only get 1 offering in modulation and no FM modulation from what I see.

The Hickok 288X is quite the opposite. You have control over about anything. The IG102 did align my SX-43 rather well - though I would have preferred the 288-X.



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That looks OK to me assuming Band B is selected.
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Old 5th Aug 2020, 10:08 am   #137
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Default Re: Another Hallicrafters Sky Champion S20.

The signal generator's setting and frequency counter's reading tie up with the counter indicating approximately 455kHz.

I'm not so sure about the scope display. The period of a 455kHz sine wave is about 2.2uS, so if the scope's time base is set to 0.5uS calibrated a complete cycle should span 4.4 divisions on the screen.

In post 133 and its accompanying pictures you say that the time base is set to 0.1uS. It looks more like 1uS to me, but it's difficult to tell from the picture.
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Old 5th Aug 2020, 10:50 am   #138
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Default Re: Another Hallicrafters Sky Champion S20.

That seems to prove that all's well with the signal generator, frequency counter and the 'scope.

Without altering the frequency of the signal generator I would now reduce the output of the signal generator to give 50mV Peak to Peak at g1 of the mixer then transfer the 'scope probe to the anode of the mixer (pin 3) and see what's what.

Lawrence.
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Old 5th Aug 2020, 2:49 pm   #139
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Default Re: Another Hallicrafters Sky Champion S20.

I reduced the output from the sig gen, adjusted scope a little with the probe on pin 3 of mixer.

The pix appear to indicate the mixer is ok- is that the case?

Bear in mind my scope is very vintage and probably has not been calibrated since the 1980s. I pretty much use it as a deflection detector and the settings/determination of magnitude with it is less relevant for me than the visual indication of magnitude shifts (I cannot attest the scope's settings function consistent across their ranges enough to rely on what it is qualitatively telling me - such as what a modern digital scope can do easily).

Quote:
Originally Posted by ms660 View Post
That seems to prove that all's well with the signal generator, frequency counter and the 'scope.

Without altering the frequency of the signal generator I would now reduce the output of the signal generator to give 50mV Peak to Peak at g1 of the mixer then transfer the 'scope probe to the anode of the mixer (pin 3) and see what's what.

Lawrence.
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Old 5th Aug 2020, 3:02 pm   #140
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Default Re: Another Hallicrafters Sky Champion S20.

If that's with 50mV Peak to Peak from the generator on g1 of the mixer then it looks like the mixer is amplifying ok, if that's the case leave the generator settings as they are and transfer the 'scope probe to g1 (the top cap) of the IF amplifier and see what's what there.

Lawrence.
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