Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Tue 19, 2021 4:39 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 12 posts ] 
Author Message
 Post subject: 12au7 sw regen.
PostPosted: Apr Sat 17, 2021 3:49 pm 
Member

Joined: Feb Thu 19, 2015 1:49 pm
Posts: 114
Has anyone built the 12au7 sw set seen on the chappy happy website. I built the 12ba6 regen from the same site and it's quite a performer,this one not so much.Just wondered if anyone else built this and maybe made some changes. This is the one with the FET rf amp. I thought it would be a great performer but such is not the case so far,would appreciate any feedback.


Top
 Profile  
 
 Post subject: Re: 12au7 sw regen.
PostPosted: Apr Sat 17, 2021 4:46 pm 
Member

Joined: May Tue 30, 2006 4:46 pm
Posts: 10924
Location: Santa Rosa, CA
Link ?

Schematic?

Rich


Top
 Profile  
 
 Post subject: Re: 12au7 sw regen.
PostPosted: Apr Sun 18, 2021 2:06 am 
Member

Joined: Feb Thu 19, 2015 1:49 pm
Posts: 114
Just enter chappyhappy radios and it will come up.There are a number of videos of radio builds. I don't even remember how I found this anyway. I guess I must of just put in regenerative radios and it came up. I have tried about three of them,the 12ba6 being the best. I just took a screen shot of the schematic when it showed on the video and built from it. I couldn't get the thing to print so I just had to keep looking at my iPad.This chappy happy character doesn't do the builds he just has them on his website along with a bunch of other junk,that why I say just enter chappyhappy radios and you'll see a bunch of videos.


Top
 Profile  
 
 Post subject: Re: 12au7 sw regen.
PostPosted: Apr Sun 18, 2021 3:35 am 
Member

Joined: Jan Sat 25, 2020 5:23 am
Posts: 700
Location: Colorado Springs, CO 80917
Apparently, chappy happy is not a website but a YouTube channel.
https://www.youtube.com/channel/UCgWqbL ... fj6ffJMgNg


Top
 Profile  
 
 Post subject: Re: 12au7 sw regen.
PostPosted: Apr Fri 30, 2021 5:41 pm 
Member
User avatar

Joined: Aug Wed 25, 2010 3:23 pm
Posts: 1506
Location: WA 98407
I tried my hand at building a Happy Chappy 12AU7 receiver. Results were not good (could not get it to work), even though I built it with care. There are far better circuits to try.

Tom


Top
 Profile  
 
 Post subject: Re: 12au7 sw regen.
PostPosted: May Fri 07, 2021 1:55 am 
Member

Joined: Feb Thu 19, 2015 1:49 pm
Posts: 114
I am pretty much in agreement with all thumbs on this one. I have gone over this thing again and again I even rewound the coil again because the first looked a little sloppy. It didn't make any difference. I eliminated the transistor rf amp to no avail. I eliminated the 30pf in the antenna circuit and use a small air variable in its place. My tuned loop antenna won't work at all,so just use the long wire strung up in my basement. Not much luck there either. What works best is a few jumper wires strung together by my basement window. I can receive a few stations,very hard to separate,that's where the variable in the antenna circuit comes in. I connect the antenna lead right to the tuning capacitor and with patience I can get a few channels. Not the best set I have built for sure.


Top
 Profile  
 
 Post subject: Re: 12au7 sw regen.
PostPosted: May Sat 08, 2021 11:27 pm 
Member

Joined: Nov Sun 22, 2015 4:51 pm
Posts: 40
I recommend this twin-triode receiver: https://www.frostburg.edu/personal/latta/ee/twinplex/twinplex.html It will work just as well with a 12AU7 twin triode; a 12AU7 can be wired for 6.3 V heating.


Top
 Profile  
 
 Post subject: Re: 12au7 sw regen.
PostPosted: May Sun 09, 2021 1:26 am 
Member

Joined: Feb Thu 19, 2015 1:49 pm
Posts: 114
I have built a twinplex very similar to the frostburg,that one works great on sw and BC.


Top
 Profile  
 
 Post subject: Re: 12au7 sw regen.
PostPosted: May Wed 19, 2021 6:37 pm 
New Member

Joined: Mar Fri 14, 2014 1:32 am
Posts: 19
The antenna input on this design is very suspect. The separate antenna coil suggests a low impedance antenna, but then you have 30pF in series with the antenna. Assuming the antenna coil is intended for 50 Ohms (just for sake of argument), that means that well over 90% of the input signal is being lost across the 30pF (Xc = 757 Ohms). For a low-Z antenna I'd remove the 30pF entirely. For a hi-Z antenna I'd keep the 30pF but connect the antenna to the top of the main tuning coil.


Top
 Profile  
 
 Post subject: Re: 12au7 sw regen.
PostPosted: May Thu 20, 2021 4:51 pm 
Member

Joined: Feb Thu 19, 2015 1:49 pm
Posts: 114
I did away with the 30 pf. I do connect the antenna to the top of main tuning coil. I connect a small air variable trimmer between the antenna and main coil. I get plenty of signal now but the selectivity is terrible. This I can compensate for a little bit with the trimmer but it is still not one of my favorite builds.


Top
 Profile  
 
 Post subject: Re: 12au7 sw regen.
PostPosted: May Fri 21, 2021 1:17 am 
Member

Joined: Dec Sun 14, 2008 3:33 pm
Posts: 1196
Location: Tokyo
Quote:
I did away with the 30 pf. I do connect the antenna to the top of main tuning coil. I connect a small air variable trimmer between the antenna and main coil. I get plenty of signal now but the selectivity is terrible.


You've run into a basic limitation of regenerative detectors: they work best with a minimum of signal. That is, they are most sensitive and most selective when the incoming signal level is as low as possible. The upshot is naturally the detected audio volume is low.

This means you usually have to 'throw away' a lot of the signal before it even gets to the detector. Sometimes most of it. This is emphatically so on higher SW frequencies. That transistor RF amp in the original design is not there to provide gain, it's there to control the signal level without loading down the detector. You can adjust signal with just a pot across the input coil (antenna going to the wiper) or with a small VC in series with the antenna lead, but they will shift the frequency as you adjust the signal level. The transistor RF amp doesn't do that, at least not to the same extent.

You may find that when the signal level is adjusted so that the regeneration operates smoothly, the detected audio level is too low. Why? Because tube audio amplifiers work extremely inefficiently at 12V. You have two choices: add more audio amplification or raise the B+ to 45V or higher.

Rob


Top
 Profile  
 
 Post subject: Re: 12au7 sw regen.
PostPosted: Aug Tue 10, 2021 2:28 pm 
Member

Joined: Feb Thu 19, 2015 1:49 pm
Posts: 114
Finally got my 12au7 regen working good. I hate giving up on a build! I replaced the toroid coil with a coil wound on a pill bottle. It's 25 turns of I think number 26 magnet wire with 7 turns for the tickler. I also ran a separate line of 45 volts for the operating voltage. I now have quite a few stations separated nicely. I use a little radio shack speaker amplifier and it works quite well. Didn't like that toroid anyway,with that many turns it's very tedious to wind.


Top
 Profile  
 
Post New Topic Post Reply  [ 12 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 5 guests



Search for:
Jump to:  


































Privacy Policy :: Powered by phpBB