The PHILCO Phorum
AS4 Hobbyists Radio - Printable Version

+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Various and Sundry Categories (https://philcoradio.com/phorum/forumdisplay.php?fid=37)
+--- Forum: Other Radios (Non-Philco) (https://philcoradio.com/phorum/forumdisplay.php?fid=12)
+--- Thread: AS4 Hobbyists Radio (/showthread.php?tid=21956)


AS4 Hobbyists Radio - Daniel Bingamon - 12-24-2020

So, there was a schematic of a basic AA5 type radio online that read everything in an easy-to-read top-down manner -- but it had a lot of errors.  Nevertheless, once corrected it would be a good baseline to make a hobbyists based AA5 like radio.  But subtract the rectifier and add a full wave bridge, add power isolation and a filament transformer.  The original schematic had 6V tubes, I changed it to a 12V system and the type of tubes fit neatly into relay sockets.   Also, the rig has a built-in GFCI which is to help keep the tinkerer a bit more safe (I know, that's a relative term especially since there are stored capacitances).  I named this homemade contraption the AS4, American Safe Four Hobbyists Tube Radio.

It's a work in progress.  I'm working on a Patreon video to share the construction of this set.
Being a Hobbyists radio, the plan is to make it where additional bands and other features can added over time either by myself or others that care to build one.

I'd like to share the schematic here and I'm open to any comments on it and/or spotting of any glaring errors.  (I found one earlier today just before this post).
Those of you on the other side of the ocean will find it nice that you can substitute transformers

[Image: http://kingsmills.us/Radio/AS4%20Radio/AS4.jpg]

RE: AS4 Hobbyists Radio - Daniel Bingamon - 12-24-2020

My drawings are in TinyCad, along with additions to it's library for vacuum tubes:
http://kingsmills.us/Radio/AS4%20Radio/

RE: AS4 Hobbyists Radio - RodB - 12-24-2020

You might want to lower the screen voltage of V1 and V2. Use a screen grid resistor off B+ and feed the voltage to the two grids. This will result in less screen grid current with little effect on output. Maybe extend the life of the tube.

RE: AS4 Hobbyists Radio - Daniel Bingamon - 12-24-2020

Thanks, that's information.   I'll have to figure out how much to change it by.

RE: AS4 Hobbyists Radio - Radioroslyn - 12-24-2020

The typical RMA color code for the output transformer's primary would be red would connect to B+ and blue to the plate. If it was a p/p transformer the blue and brown would be for the plates and red for the B+.
Nowdays transformers have different colors with no rhyme or reason.

You got the ant section of the tuning cap ganged with the oscillator trimmer cap.

Lose the 12sa7 and use a 12BA7, much better performance.

Increase the voltage rating of the filters to 250v. With a bridge rectifier you're going to be @ abt 170vdc.

Avc circuit is a little odd as it adds avc voltage to the oscillator circuit? I'd ground the tuning cap and float L1. But to each their own.

RE: AS4 Hobbyists Radio - vinzer - 12-24-2020

the 12sk7 screen grid should not be connected to the plate but to b+.

RE: AS4 Hobbyists Radio - Daniel Bingamon - 12-30-2020

Good catches.  I'm correcting it.

I have a question.  Most AA5 drawings have the second anode to the diode on the 12SQ7 to ground.   Would tying both anodes together cause noise or something?

RE: AS4 Hobbyists Radio - Arran - 12-31-2020

I guess you mean the second detector or AVC diodes, it seems to have been a matter of preference by the manufacturer, or perhaps the engineer, what to do with the second diode, if they chose not to use both of them. I've seen some where both plates were tied together as well as tying the plate to ground, I don't think that one approach won out more then the other. In fact I have some radios where they used a 6H6 double diode, rather then the pair in a 6Q7, and they tied both diodes together, other then for tube stuffing the chassis why even bother?
Regards
Arran

RE: AS4 Hobbyists Radio - Daniel Bingamon - 01-15-2021

Yes, that is what I meant.   The drawing up above is a link so it should show the latest updates.

RE: AS4 Hobbyists Radio - Daniel Bingamon - 01-17-2021

My latest revision of the schematic is based on a realization that the rotor on the variable capacitor is common to both the broadcast portion and the oscillator portion. The previous design would not have worked. It would have shorted the AGC circuit.

RE: AS4 Hobbyists Radio - Daniel Bingamon - 01-24-2021

[Image: http://bingamon.com/Radio/AS4%20Radio/Photos/as4-4.jpg]Here is the latest photo of it.  Getting closer to completion.

RE: AS4 Hobbyists Radio - Daniel Bingamon - 05-16-2021

My latest update on this.  I made a PC Board for the parts and tubes.  Revised the schematic.
Also found that the capacitor across the Plate and Cathode of the 12L6 was causing oscillations.  It was moved to go across the audio transformer instead.  Now the audio is crystal clear but I was having issues with the local 500KW AM station that is 3 miles away by air getting into everything.   I'm replacing the IF transformers yet again and will employ some additional shielding.

RE: AS4 Hobbyists Radio - OZ4 - 05-16-2021

The rectifier section make me think about the wall wart transformers that are so ubiquitous today. 

Everyone I have taken apart have a common mode choke with a safety cap and a bridge rectifying the line AC and filter cap. 

It's all ready to go for 170vdc. Just don't get zapped.

RE: AS4 Hobbyists Radio - Daniel Bingamon - 09-19-2021

I want to thank everyone here that helped with this.   I finally reversed the second IF transformer and it aligned properly.
Here are photos of it in it's cabinet.

[Image: https://bingamon.com/Radio/AS4%20Radio/AS4%20Receiver%20Front.jpg]

And 
[Image: https://bingamon.com/Radio/AS4%20Radio/as4%20Receiver%20Back.jpg]