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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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22nd Nov 2017, 9:39 pm | #41 |
Diode
Join Date: Nov 2008
Location: Corning, NY USA
Posts: 8
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Re: Most Minimal Superhet
Here is a one tube superhet I built a while back.
http://makearadio.com/tube/6ba7-superhet.php 73, Dave, N2DS
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Amateur Radio N2DS |
22nd Nov 2017, 10:25 pm | #42 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
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Re: Most Minimal Superhet
Yes this is the important parameter for the converter, this is why an ECH35 is superior to a 6k8.
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23rd Nov 2017, 9:54 am | #43 | |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,060
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Re: Most Minimal Superhet
Quote:
At low frequencies, one of the circuits will be at a slightly higher frequency than the other, so put a core in it; add a turn; until inductance is raised to bring it in-line with the other. Or, separate the turns of the other, until its frequency is raised. At high frequencies, one of the frequency will be slightly higher than the other. So, add a trimmer capacitor across it to bring the frequency down. This will mess up the low-frequency end, but repeating a few times will converge. Don't adjust trimmers at the low-frequency end, because their effect is heavily diluted by the full capacitance of the variable tuning capacitor, so you'll have to make a big adjustment to have any effect, which'll screw things completely at the HF end! It is certainly possible to be 'good enough', let's face it, if superhets can be made to track sufficiently well, when the two tuned circuits are at DIFFERENT frequencies, a TRF with them at the SAME frequency should be a doddle! |
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23rd Nov 2017, 9:59 am | #44 | |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,060
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Re: Most Minimal Superhet
Quote:
Could you have reflexed the AF, back into the frequency changer, and got a bit of AF amplification to drive the headphone? Or did you try it and just found it's too prone to instability? |
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23rd Nov 2017, 10:41 am | #45 |
Nonode
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,083
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Re: Most Minimal Superhet
The ECH81 I have is a Russian clone.
I am still waiting to receive components & am like a cat on a hot tin roof. |
23rd Nov 2017, 12:01 pm | #46 | |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
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Re: Most Minimal Superhet
Quote:
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23rd Nov 2017, 4:11 pm | #47 |
Nonode
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,083
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Re: Most Minimal Superhet
Several packets of resistors & capacitors came just now through the letterbox.
I saw the postie still had his summer cargo pants on and on a day with gusts seemingly blowing from the open door of a fridge. Perhaps there's a contest at the depot over who is the hardest? |
24th Nov 2017, 2:09 am | #48 |
Diode
Join Date: Nov 2008
Location: Corning, NY USA
Posts: 8
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Re: Most Minimal Superhet
Here is a real 1 valve superhet that a fellow in Canada built a few years ago.
http://electronbunker.ca/eb/OneTubeSuper.html I don't think it gets better than that. Everything reflexed. Dave
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Amateur Radio N2DS |
24th Nov 2017, 3:10 am | #49 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,060
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Re: Most Minimal Superhet
Wow!!!!
RF Signal through valve... IF appears in push-pull at two anodes. Filtered and fed back to valve as a common-mode signal... Amplified common-mode output signal extracted, from letter and detected... AF fed back to valve, amplified a third time, drives phones or speaker! So the valve amplifies at 3 different frequencies! |
25th Nov 2017, 6:51 pm | #50 |
Nonode
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,083
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Re: Most Minimal Superhet
I have been carrying on with mine, robbing parts from the old kit radio. I removed the tuning capacitor & the drive pulleys.
These have now been fitted on the new chassis carefully aligned to use the reduction afforded by the spindle and pulley. I don't know the precise ratio. Is the accepted colour for RF and oscillator wires usually red & blue? Those are the colours Denco used anyway. I ought to complete the detector first and put 4**Khz into the primary of the only IFT. If I get a 1Khz tone from the speaker then I am on the right track. |