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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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5th Apr 2020, 11:04 pm | #41 | |
Hexode
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Re: Hallicrafters Sky Champion S20
Quote:
I note the comments regarding the 250 pf silver mica capacitor on the base of the 6J5. Still looking for one. Lynton
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5th Apr 2020, 11:45 pm | #42 |
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Re: Hallicrafters Sky Champion S20
I was referring to the pitch control. If you can vary the BFO above and below 455 kHz you'll be able to resolve LSB and USB signals.
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6th Apr 2020, 9:48 am | #43 |
Nonode
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Re: Hallicrafters Sky Champion S20
Hi Lynton, I've put a 250pF 350v silver mica in the post. A ceramic would also have been OK. Cheers, Jerry
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6th Apr 2020, 10:22 am | #44 |
Dekatron
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Re: Hallicrafters Sky Champion S20
I've never worked on one of these but make sure that the BFO frequency is supposed to be the IF and not IF/2 like on some receivers.
Lawrence. |
6th Apr 2020, 10:44 am | #45 | |
Hexode
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Re: Hallicrafters Sky Champion S20
Quote:
The effect of the pitch control is very small indeed. I did (after much twiddling) manage to clarify an SSB signal but I think (on good advice) the mica capacitor in the can underneath the 6J5 is the most likely culprit. There is one in the post to me from a fellow forum member (most appreciated). I think after all the adjustments that have been made I will have to do a re-alignment, and probably reduce the amount of coupling that I added. Lynton
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6th Apr 2020, 3:09 pm | #46 | |
Hexode
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Re: Hallicrafters Sky Champion S20
Quote:
Lynton
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6th Apr 2020, 3:15 pm | #47 | |
Hexode
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Re: Hallicrafters Sky Champion S20
Quote:
To be honest I cannot find any information about the BFO, its operation ,setting, or basic frequency. Documentation about the S20 is very scant, but there is much more about its successor the S20 R, which I believe was a very good receiver. I would love to have a go at one of them! Cheers Lynton
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6th Apr 2020, 3:39 pm | #48 |
Dekatron
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Re: Hallicrafters Sky Champion S20
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6th Apr 2020, 4:46 pm | #49 |
Hexode
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Re: Hallicrafters Sky Champion S20
Hi Lawrence been searching for more info but no luck. However the S20R uses an almost identical setup and states that the frequency is 455KHz.
Cheers Lynton
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6th Apr 2020, 4:52 pm | #50 |
Dekatron
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Re: Hallicrafters Sky Champion S20
That's probably it then.
Lawrence. |
7th Apr 2020, 12:50 pm | #51 | |
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Re: Hallicrafters Sky Champion S20
Quote:
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7th Apr 2020, 1:33 pm | #52 |
Dekatron
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Re: Hallicrafters Sky Champion S20
I had a Hallicrafters of that era which had a front panel BFO injection level control as standard, I increased the value of the injection coupling capacitance a bit and used the control accordingly which I sometimes found useful.
The level control varied the HT supply to the BFO valve. Lawrence. |
7th Apr 2020, 5:32 pm | #53 | |
Heptode
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Location: Cedar Grove, Wisconsin, USA.
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Re: Hallicrafters Sky Champion S20
Quote:
Dave, USradcoll1. |
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7th Apr 2020, 6:35 pm | #54 |
Hexode
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Re: Hallicrafters Sky Champion S20
Replacement capacitor arrived this morning (thanks Jerry), installed in radio but could not detect any oscillation. Turned out to be my unreliable scope, but after some effort it did display a BFO signal.
Set BFO frequency using scope. Tuned to a faint AM station and played around with RF and AF gain but no heterodyne. Re aligned IF (don’t have a frequency counter but can check output of SG using my Trio R600). It was a little out but re aligned ok. Again no heterodyne. Stayed on faint AM station and slowly adjusted BFO transformer until a heterodyne could be heard. Tuned around bands until I found some SSB and with careful adjustment could resolve the speech. What do I draw from all this? My scope is probably giving false information. I need a frequency counter to to do this kind of work accurately. I am probably expecting too much from such an old radio. What I was pleased about? All the help and suggestions from forum members, especially Jerry who tested all the valves and provided a new capacitor foc. The amount of extra knowledge I have gained again from forum members (and the Internet). The whole process was enjoyable/confusing/frustrating/satisfying in many different ways. Once again thanks to everyone for all the help. I look forward to the next radio. Cheers Lynton
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7th Apr 2020, 6:44 pm | #55 |
Dekatron
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Re: Hallicrafters Sky Champion S20
A 'scope is really a rather inappropriate tool for adjusting the frequency of this sort of oscillator: for the BFO to work it needs to be within a couple of KHz of the receiver's intermediate-frequency (455KHz) - which means that your 'scope would need its timebase to be accurately settable to better than 0.5%
It was almost certainly never that accurate when manufactured! And even if it was, the timebase-frequency control can't be read to that level of accuracy anyway. Digital frequency-counters are remarkably cheap these days, and make this sort of work *so* much easier. |
14th Apr 2020, 4:56 pm | #56 | |
Heptode
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Re: Hallicrafters Sky Champion S20
Quote:
I'm going to thin out the collection as soon as this foolishness is over. Dave, USradcoll1 |
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14th Jul 2020, 4:54 pm | #57 |
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Re: Hallicrafters Sky Champion S20
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2nd Jan 2021, 12:50 am | #58 | ||
Diode
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Re: Hallicrafters Sky Champion S20
Quote:
I got the can loose too but don't have enough slack in the wires coming in to it to get it down that far so I can replace the components. Did you disconnect the far end of the wires first? John Limbach, K8NN Last edited by Station X; 2nd Jan 2021 at 10:44 am. Reason: Email address removed. |
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4th Jan 2021, 4:39 am | #59 |
Pentode
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Re: Hallicrafters Sky Champion S20
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4th Jan 2021, 10:57 am | #60 | |
Dekatron
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Re: Hallicrafters Sky Champion S20
Quote:
Lawrence. |
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