Posts: 53
Threads: 7
Joined: Nov 2020
City: KINGS MILLS
State, Province, Country: OH
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]
Posts: 53
Threads: 7
Joined: Nov 2020
City: KINGS MILLS
State, Province, Country: OH
My drawings are in TinyCad, along with additions to it's library for vacuum tubes:
http://kingsmills.us/Radio/AS4%20Radio/
Posts: 1,072
Threads: 43
Joined: Feb 2015
City: Roseville, MN
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.
Posts: 53
Threads: 7
Joined: Nov 2020
City: KINGS MILLS
State, Province, Country: OH
Thanks, that's information. I'll have to figure out how much to change it by.
Posts: 7,294
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
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.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 12-25-2020, 12:06 AM by Radioroslyn.)
Posts: 214
Threads: 16
Joined: May 2010
City: Kokomo, IN
the 12sk7 screen grid should not be connected to the plate but to b+.
Posts: 53
Threads: 7
Joined: Nov 2020
City: KINGS MILLS
State, Province, Country: OH
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?
Posts: 4,801
Threads: 54
Joined: Sep 2008
City: Sandwick, BC, CA
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
Posts: 53
Threads: 7
Joined: Nov 2020
City: KINGS MILLS
State, Province, Country: OH
Yes, that is what I meant. The drawing up above is a link so it should show the latest updates.
Posts: 53
Threads: 7
Joined: Nov 2020
City: KINGS MILLS
State, Province, Country: OH
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.
Posts: 53
Threads: 7
Joined: Nov 2020
City: KINGS MILLS
State, Province, Country: OH
[Image: http://bingamon.com/Radio/AS4%20Radio/Photos/as4-4.jpg]Here is the latest photo of it. Getting closer to completion.
Posts: 53
Threads: 7
Joined: Nov 2020
City: KINGS MILLS
State, Province, Country: OH
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.
Posts: 285
Threads: 27
Joined: Nov 2012
City: Tehachapi. California
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.
!!!!!!!!!!!!!!!!!!!RESISTANCE IS FUTILE!!!!!!!!!!!!!!!!!!!!!!
/\/\/\/\/\/\/\/\/\
[Image: http://philcoradio.com/phorum/images/smi...on_eek.gif] Chris
Posts: 53
Threads: 7
Joined: Nov 2020
City: KINGS MILLS
State, Province, Country: OH
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/A...0Front.jpg]
And
[Image: https://bingamon.com/Radio/AS4%20Radio/a...20Back.jpg]
Users browsing this thread: 1 Guest(s)
|
|
Recent Posts
|
|
6TPZ and 5TPO Radio Help
|
| Welcome to the Phorum, R3Sons! I have very limited experience with car radios other than installing custom radios back ...GarySP — 01:08 PM |
|
462ron
|
| OK, I need to rename this thread to say..Eico 368 TV/FM Sweep Generator instead of the current title..Heathkit Sweep Gen...462ron — 12:49 PM |
|
6TPZ and 5TPO Radio Help
|
| Hello, I have a Philco (Ford) 6TPZ and a 5TPO radio. I replaced the electrolytic capacitors in both. I have the SAMS m...R3Sons — 12:29 PM |
|
The list of my radio & TV collection!
|
| Hello Peter,
Thank you for posting that !!
Sincerely Richardradiorich — 09:40 AM |
|
Eico 232 VTVM Schematic
|
| It's a microwave antenna. ?;-p?. I substituted 1N4002s off the 6.3 vac winding for the 1.5 volt battery. Uniprobe is the...RodB — 05:50 PM |
|
Eico 232 VTVM Schematic
|
| Try BAMA for a schematic.
Looks like a replacement power source for the D battery has been installed. The tube may be...Chas — 04:51 PM |
|
Eico 232 VTVM Schematic
|
| Is that a battery holder?morzh — 04:43 PM |
|
Eico 232 VTVM Schematic
|
| A friend gave me this Eico 232 VTVM and I'm having trouble locating the schematic for it. This one seems to be a later v...RodB — 04:17 PM |
|
Var resistor id
|
| Considering what it is in series with, I doubt there should be any power requirements. Of course, we should
know wher...morzh — 03:23 PM |
|
Var resistor id
|
| Trim pot, about 1/2 watt part of focus divider. As stated 2k ohms.
This appears to be a rusty chassis, resolder all ...Chas — 03:19 PM |
|
Who's Online
|
There are currently 8230 online users. [Complete List]
» 3 Member(s) | 8227 Guest(s)
|
|
|
|
 
|
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
