AVO MK I signal generator - UK Vintage Radio Repair and Restoration Discussion Forum

Mullard · 9th Aug 2007, 11:20 pm

I have an AVO signal generator MK I, that I bought some time ago on ebay. I would like to get hold of the circuit diagram although I have actually managed to get it working without (it is quite simple). The major problem on mine was an open circuit choke (looked like a mechanical break where the wire was attached to the tag, and so easily resoldered by bending the tag slightly), a low emission L63, and dirty turret contacts. I use it regularly and have been amazed at how accurate it is after all these years.

John

kalee20 · 10th Aug 2007, 1:43 pm

Hi Mullard, is this the 2-valve item (both L63's?) I have an instruction manual for the All-Wave Oscillator but dunno if this is the Mk 1 or not. It is in PDF form, if you send me a PM then I will e-mail it to you.

Incidentally, I've always thought it inelegant that the power supply in this equipment uses a half-wave rectifier from a mains transformer!

Mullard · 10th Aug 2007, 10:48 pm

Hi Kalee20

The Avo Signal Generator is different from the All-Wave Oscillator. The AVO SG uses the 8D3 as the RF oscillator and the L63 as the AF oscillator. I have taken a few photos, and the SG and these are attached.

On reopenoing the box I remembered better the repair to the coil. I actually had to extend the coil wire and used some silicon to hold the join stady. you can see this in the last photo.

Many thanks for your offer, I would be intersted, even though mine is different. I will send you a PM.

John

Phil G4SPZ · 17th Aug 2007, 5:24 pm

John,

Can I thank you for the excellent quality of the photos you posted? I have now looked inside my Avo, and your photos have been most helpful in working out how to restore it to original condition, although this will be quite a big job - it's had quite a lot of work done to it

Can I ask you a couple of questions, please? Firstly, do you know the purpose of the socket marked "Force" which leads from the oscillator enclosure? I am guessing that this is a high-level RF signal straight from the oscillator not via the attenuator. And secondly, the terminal panel on mine is bolted through the lower case half. I think this is a modification, is yours the same?

With many thanks,

Phil

Mullard · 19th Aug 2007, 12:22 am

Phil,
Glad you found the photos useful, let me know if you need any other views and I will post them for you. I have an instruction manual for mine, and I will scan it next week and send it to you if you send me a pm.
You are correct about the force output, it does provde a direct unattenuated output. You should have a plug with a long tube attached to push down the spout and make a connection.
There are four screws on the end through the bottom half of the case and these must be removed, along with the four screws on the bottom, to take the unit to pieces. The panel that holds the connectors will then float freely, but I have had no trouble getting the screws back in.
Disassembly is quite straightforward, and the turret can be removed to clean the contacts. I used a rouge paste that is quite gentle on the silver plated contacts.
I traced out the circut of the modulator, as mine wasn't working, and I will include this wth the manual.
The RF oscillator is a Collpits and is similar to other signal generators of the era, although the AVO is built like a tank and to a high standard.
Good luck with it.
John

Phil G4SPZ · 19th Aug 2007, 12:50 am

Hi John,

That's very helpful, many thanks. I'll PM you my e-mail address and would really appreciate the manual and circuit. I don't have the long plug that goes into the 'force' socket but I only expect to use the 'uV' and 'LF' outputs anyway.

My AVO has clearly led a hard life. The case is quite battered and dented with some paint chipped off, compared with your pristine example, and it had been splashed with red paint. Someone has actually made a replacement backplate for the turret enclosure, one of the knobs is home-made, and the wires to the output sockets have been left disconnected. So I will probably do a repair rather than a restoration, and use it 'on the road', so to speak - I don't really need any more RF signal generators in the shack, I already have four others!

Good idea on the jewellers' rouge for cleaning the turret contacts. The turret in my AVO looks fine, but I've not removed the turret itself yet.

Again, thanks for your help and interest.

Phil

9th Aug 2007, 11:20 pm	#1
Mullard Pentode Join Date: Jul 2007 Location: Clophill, Bedfordshire, UK. Posts: 127	AVO MK I signal generator I have an AVO signal generator MK I, that I bought some time ago on ebay. I would like to get hold of the circuit diagram although I have actually managed to get it working without (it is quite simple). The major problem on mine was an open circuit choke (looked like a mechanical break where the wire was attached to the tag, and so easily resoldered by bending the tag slightly), a low emission L63, and dirty turret contacts. I use it regularly and have been amazed at how accurate it is after all these years. John

10th Aug 2007, 1:43 pm	#2
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,087	Re: AVO MK I signal generator Hi Mullard, is this the 2-valve item (both L63's?) I have an instruction manual for the All-Wave Oscillator but dunno if this is the Mk 1 or not. It is in PDF form, if you send me a PM then I will e-mail it to you. Incidentally, I've always thought it inelegant that the power supply in this equipment uses a half-wave rectifier from a mains transformer!

10th Aug 2007, 10:48 pm	#3
Mullard Pentode Join Date: Jul 2007 Location: Clophill, Bedfordshire, UK. Posts: 127	Re: AVO MK I signal generator Hi Kalee20 The Avo Signal Generator is different from the All-Wave Oscillator. The AVO SG uses the 8D3 as the RF oscillator and the L63 as the AF oscillator. I have taken a few photos, and the SG and these are attached. On reopenoing the box I remembered better the repair to the coil. I actually had to extend the coil wire and used some silicon to hold the join stady. you can see this in the last photo. Many thanks for your offer, I would be intersted, even though mine is different. I will send you a PM. John Attached Thumbnails

17th Aug 2007, 5:24 pm	#4
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: AVO MK I signal generator John, Can I thank you for the excellent quality of the photos you posted? I have now looked inside my Avo, and your photos have been most helpful in working out how to restore it to original condition, although this will be quite a big job - it's had quite a lot of work done to it Can I ask you a couple of questions, please? Firstly, do you know the purpose of the socket marked "Force" which leads from the oscillator enclosure? I am guessing that this is a high-level RF signal straight from the oscillator not via the attenuator. And secondly, the terminal panel on mine is bolted through the lower case half. I think this is a modification, is yours the same? With many thanks, Phil __________________ Phil Optimist [n]: One who is not in possession of the full facts

19th Aug 2007, 12:22 am	#5
Mullard Pentode Join Date: Jul 2007 Location: Clophill, Bedfordshire, UK. Posts: 127	Re: AVO MK I signal generator Phil, Glad you found the photos useful, let me know if you need any other views and I will post them for you. I have an instruction manual for mine, and I will scan it next week and send it to you if you send me a pm. You are correct about the force output, it does provde a direct unattenuated output. You should have a plug with a long tube attached to push down the spout and make a connection. There are four screws on the end through the bottom half of the case and these must be removed, along with the four screws on the bottom, to take the unit to pieces. The panel that holds the connectors will then float freely, but I have had no trouble getting the screws back in. Disassembly is quite straightforward, and the turret can be removed to clean the contacts. I used a rouge paste that is quite gentle on the silver plated contacts. I traced out the circut of the modulator, as mine wasn't working, and I will include this wth the manual. The RF oscillator is a Collpits and is similar to other signal generators of the era, although the AVO is built like a tank and to a high standard. Good luck with it. John

19th Aug 2007, 12:50 am	#6
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: AVO MK I signal generator Hi John, That's very helpful, many thanks. I'll PM you my e-mail address and would really appreciate the manual and circuit. I don't have the long plug that goes into the 'force' socket but I only expect to use the 'uV' and 'LF' outputs anyway. My AVO has clearly led a hard life. The case is quite battered and dented with some paint chipped off, compared with your pristine example, and it had been splashed with red paint. Someone has actually made a replacement backplate for the turret enclosure, one of the knobs is home-made, and the wires to the output sockets have been left disconnected. So I will probably do a repair rather than a restoration, and use it 'on the road', so to speak - I don't really need any more RF signal generators in the shack, I already have four others! Good idea on the jewellers' rouge for cleaning the turret contacts. The turret in my AVO looks fine, but I've not removed the turret itself yet. Again, thanks for your help and interest. Phil __________________ Phil Optimist [n]: One who is not in possession of the full facts