Avo all wave oscillator circuit information.

[tis your junk]

Hello to all,
I'm still new to these forums, but this looks to right place to post this request.
I am looking for the circuit diagram for a AVO Avo all wave oscillator to help restore a non working example.

Any help with this would be much appreciated.

Many thanks

TYJ

[Station X]

A bit of searching pulled out this thread which contains what you require in post 4:-

https://www.vintage-radio.net/forum/...ad.php?t=10042

[tis your junk]

Ok, thanks to all of the people who responded. I now have a manual and circuit diagram. UnfortunateIy it would appear that the power input i.e. switch and cabling has been stripped out so I'm not sure how these should be loomed. If you or anyone else could take some photos of what it should look like I'd much appeciate it.

Fortunately everything else seems to be there!


Thanks
TYJ

[John M0GLN]

Hi TYJ

Are these photos of any help to you? I don't know if they made more than one model, if they did, hopefully this is the right one.

John

[tis your junk]

Hi John
Jeeez guys you always come up with the answer!
The pictures are a great help, basically I'm missing all the bits to the right of the wooden box as shown in the first picture. These must be in my late fathers shed somewhere ... send out the search parties if I'm not back by the new year!

Thanks again

TYJ

[Top Cap]

http://www.isoplethics.co.uk/transfor.htm

The above website is closing down! Tragic - they have some useful parts one of which is the mains transformer MT-1 for around £15.

It has a 6.3V winding at 1.5A to run both L63 valves in the Avo Oscillator.

You also need 100V though and this tranny gives either 200, 225 or 250V!
You could use the 200V tap and reduce with a series resistor or try using the 200 - 250 taps as a 50V source to a bridge rectifier. Perhaps better, a voltage doubler circuit to give you something near to 100V.
The thing is, the tranny is nice and small to fit into the case but hurry before Isoplethics finally shuts!
Les

[tis your junk]

Hi Guys
Firstly many thanks for all your help, photos etc, and a great idea from Top Cap.

I did however manage to find the transformer switch etc and have started the process of re-building testing etc.
The model I have is not quite the same as that shown in the circuit diagram available via this forum.

1 On applying 240v volts to what appears to be the primary (it does not have enough tapes for 200 -250) I get 60 not 100 volts, with no evidence of heating etc. BUT 6.5 volts is available from the heater windings (both circuits unloaded). Could this be correct or is the transformer bust and if so how has it failed (shorted windings?) My hand book quotes the HT battery as being 75 volts so 60 volts from the secondary could be right

2 I seem to remember a wire (earth?) that connected the two halves together can anyone tell me where that connected to and from?

3 The westinghouse rectifier is and intresting beast, and fun to test! I managed to do this thanks to other threads within this forum (thanks guys) The indication was that like electrolytic capacitors they would benefit from being reformed after long periods of "rest" How is this done ? any information greatfully received!

4 Finally what age could this equipment be? Where these oscillators only post war or could they be before that?

Thanks again

Tis your junk

[Top Cap]

I have attached a section of the drawing that shows a date in 1946 so must be around that time.
My particular oscillator did not have an earthing wire, I assumed that the screws earthed the two items (cast front panel and rear cover with psu) together though nowadays it is mandatory to separately earth all metalwork, if not just for safety but EMC .
Did you measure the transformer off load? I replaced the original westinghouse with a 1N4007 silicon and 100 Ohm series resistor, the electrolytics also looked dodgey so were replaced. One of the most important caps is the output. It will have HT on it if leaky, someone had already replaced the one in my unit with two 1kV caps in series, maybe they had a misadventure in the past and did not want a repeat .
If the tranny has a shorted turn it will start to cook, better to check for 100V without any smoothing/rectifier circuit attached. Check the transformer core keeps cool.
Les

Edit: To avoid any confusion, the output capacitor referred to is the LF output C1.
The RF output is linked from an isolated coil.

[Radio_Dave]

I'd change the electrolytics first and then see what the voltages are like. I wouldn't bother reforming them. I've go two of these AWO's and the caps were virtually short circuit on both and bulging everywhere!

I think your probably refering to this thread https://www.vintage-radio.net/forum/...hlight=avo+awo
in which case, you'll see that it would be preferential to keep the Westinghouse, if at all possible

Regards
David

[tis your junk]

Hi Dave

Yep that's the one.

I intended to keep the thing as original as possible including the Westinghouse, it seems to work but not as well as some IE mine has the following characteristics

Forward bias I get 1.87 mA at 18 volts
Reverse bias gives 4.1 uA 35 volts.

The caps have already been changed to 8 mfd 450v types and both check out OK on my (borrowed) cap reformer.

Still my biggest problem is the transformer and power input which has been stripped out, with some of it being put back incorrectly, please see the photos. Some of it seem fairly straight forward IE the heater windings would appear to be the green pair, between the black/brown and pink (with yellow sleeve) I have 120 ohms and between the black and white (again yellow sleeved) I have 300 ohms Which would suggest the former was the secondary and the later the primary BUT the cable runs as they are now don't support this!

Again any advise you may have would be most welcome.

BTW as it is currently wired I get 60 volts off the unload secondary and 40 volts dc out of the "smoothing box" again with no load, which is obviously not right.


Also I would be intrested to know if you have a wire connecting the two halves of the equipment.

[Radio_Dave]

I've checked one of mine but, unfortunately, the transformer is different with no colours to the wires .

Looking at your pictures I see thet you have a black and brown stripped wire attached to the mains switch. It looks like it matches the black/brown wire inside the wooden box which is where one end of the 100v secondary connects.

If you can find the other wire to that winding and see what voltages you get

[tis your junk]

OK, the other end of the black/brown that connects to the mains switch is a yellow sleeved pink wire and this pair reads as 122 ohms on a meter, the much longer yellow and black appear to be the secondary and are 360 ohms. If I connect 240 to the brown/black and short yellow pair I get 6.5 volts on the Green pair (presumably heaters) but only 60 volts (ac) on the secondary. After the smoothing box that becomes 44 volts with a 1.2 mA load.

Interestingly if I use my variac to supply the voltage to the smoothing box it can deliver 85 volts (dc) at 2.7 mA with a 100 volt input so that would seem OK.

I assume therefore that the secondary of the transformer has been cooked/failed ( maybe when the caps failed) in a strange way so as to increase in resistance in the windings - sounds barking I know but I'm at a loss for anything else - anyone got any ideas?

So I'm now on the lookout for a replacement transformer

Thanks again for all the help.

Tis your junk