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 Post subject: Regenerative Endeavor
PostPosted: Wed Nov 21, 2012 11:51 pm 
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Joined: Wed Nov 21, 2012 10:29 pm
Posts: 35
Location: Manitoba, Canada
I am currently in the process of building a regenerative receiver for short wave using several tubes.

I have built radios with a detector and several stages of audio, but I have never included an RF amp before. That is what I need help with.

The detector in this radio is a triode. I have used 12AU7, 12AT7, etc. for such radios and thought that I could use the same for an RF amp. That would mean that one triode would be the RF amp and the other would be the detector. I thought that it would be best to use a tube with a divider between the sections for the best shielding.

I have heard that the RF amps need shielding and thought that it may be better to use separate tubes. Perhaps a 6C4 or a pentode of some sort. I have many sub miniature tubes to choose from. If any of you have ideas as to what tubes my be the best, I can look to see if I have any of the right type or similar.

Either way the tube will need to run off six volts since that is the filament voltage on the transformer that I am planning to use for the power supply.

Any advice or schematics would be great.

Also I have a general question about the forum. Sure I guess it's not in the right place, but I might as well ask while I'm writing this.

If I would like to post an image, does it have to be a URL or will a file from my computer work?

Thanks,
Eric

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 Post subject:
PostPosted: Wed Nov 21, 2012 11:58 pm 
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Location: South Florida
Quote:
If I would like to post an image, does it have to be a URL or will a file from my computer work?


Hi, Eric, and welcome!

For an image to appear, it has to be accessible from everyone's computer. This means it has to be online somewhere. I use my own website to hold images, but most people use an image-sharing service. You have to ensure you link to the image itself, not the page on, say, Photobucket, where the image appears.

Here's more info: http://theradioboard.com/rb/viewtopic.php?t=1368

Good luck with the radio.

Regards,

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 Post subject:
PostPosted: Thu Nov 22, 2012 12:16 am 
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Joined: Wed Nov 21, 2012 10:29 pm
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Location: Manitoba, Canada
I figured. Thanks for the info.

-Eric

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The world is made up of smoke and mirrors. Most people are content with being distracted by their own reflections. I will always be compelled to look behind them and gaze at the truth.


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 Post subject:
PostPosted: Thu Nov 22, 2012 5:02 am 
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Joined: Fri Feb 02, 2007 4:28 am
Posts: 23
If you plan on using an untuned stage of RF, you need not shield much at all. I think a triode would work fine. If you plan on using a tuned stage of RF, you will need very good shielding and probably would need a pentode as it would have the least tendency to form an oscillator.


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 Post subject:
PostPosted: Thu Nov 22, 2012 5:38 pm 
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Joined: Wed Nov 21, 2012 10:29 pm
Posts: 35
Location: Manitoba, Canada
Thanks for the advice. I will probably try the untuned amp first and see how it goes. Either way, I will try two separate tubes that way I can use a 6C4 as the detector and another 6C4 as the RF amp. That way if I decide to try a tuned amp I can use a 6BA6 or similar tube and it will fit in the installed socket.

-Eric

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The world is made up of smoke and mirrors. Most people are content with being distracted by their own reflections. I will always be compelled to look behind them and gaze at the truth.


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 Post subject: regen
PostPosted: Thu Nov 22, 2012 7:56 pm 
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Joined: Sun Dec 02, 2007 7:50 am
Posts: 1414
Hi Towble,

Regen sets are great arent they. I would use a "wideband"(untuned) RF amp. I also would make it Low Gain - Low noise(Grounded grid triode ?).

A regen set is already very sensitive, so you dont need the RF amp for sensitivity. But an RF amp will give some very good benefits to a regen set!

It will prevent "dead spots on the dial" caused by "antenna resonance effects". In other words it will keep the antenna from loading down the tuned circuit (sort of a buffer). Thus you wont have to change an input coupling cap when you retune stations.

It will keep the oscillating regen from radiating out of the antenna like a transmitter. Prevents interference.

It will improve the Signal to noise ratio. Mixers(even non-oscillating regen detectors) are noisy devices. So make the RF amp have just enough gain to overcome mixer noise( No more than about 10dB for example).

It could even provide a place to apply AGC.

Good Luck

73
kb0lxy - also named Eric :wink:


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 Post subject:
PostPosted: Thu Nov 22, 2012 9:09 pm 
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Joined: Wed Nov 21, 2012 10:29 pm
Posts: 35
Location: Manitoba, Canada
They are great. When I was 12 or so I got a one tube radio kit that was a regen with interchangeable coils. I love their simplicity and the way they work. I'm not one to tinker much with building a superheterodyne. They are a little more complex than I would like. Also, a regen has the ability to work on AM, CW, and SSB, without having a lot of active components.

Yes, I thought that I would try the grounded grid first. I have experimented with a regen circuit very similar to to the one I'm planning to build and it had very good sensitivity in the first place.

The benefits you mentioned are what I'm trying to gain in the receiver. Do you think that the RF amp and detector tubes should be separate or would a dual triode such as a 12AU7 work fine? Either that or I may use a 6C4 for the RF and Detector tubes.

Thanks for the info Eric!
-Eric

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The world is made up of smoke and mirrors. Most people are content with being distracted by their own reflections. I will always be compelled to look behind them and gaze at the truth.


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 Post subject:
PostPosted: Fri Nov 23, 2012 6:07 pm 
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Either way should work:

http://www.qsl.net/k5bcq/REGEN2/regen3.html
http://www.makearadio.com/tube/2-6c4.php

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 Post subject:
PostPosted: Sat Nov 24, 2012 5:55 am 
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Joined: Wed Nov 21, 2012 10:29 pm
Posts: 35
Location: Manitoba, Canada
Thanks. I'm going to build the power supply, audio, and detector sections first and then try out an RF amp. That variable coupling cap in the first circuit is a good idea. I think I'll try that so that I can get it just right.

-Eric

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The world is made up of smoke and mirrors. Most people are content with being distracted by their own reflections. I will always be compelled to look behind them and gaze at the truth.


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