Mystery radio, French? from Golborne.

[boater sam]

Thanks for the circuit Lawrence, trying to get my head around the way it is drawn out, not very English at all. Can't yet work out the AVC line, I'll get there though.

Strange with the mix of bases for the valves, B7G, B9A and Octal all in one set. Happy about the EM34 being good.

[pwdrive]

Going on the schematic I posted earlier, for the sake of it I'll call the left hand diode D1 and the right hand diode D2:

This is my take on it but see what the rest of the gang make of it, it looks like simple AGC to me as at the moment I can't see anything that introduces a delay voltage.

D2 ls the detector diode which the AGC line is derived from.

Also note that there is no cathode bias used on the mixer or the IF amp, because of that I think the contact potential of D1 is used instead, hence the high value resistor (5.6 megohm) that connects the AGC voltage from D2 to the AGC line.

Below is a link to what is basically another version of the schematic, it uses the same AGC arrangement, some voltages are given including the AGC line voltage, the voltages might have been measured under no signal conditions:

http://a402.idata.over-blog.com/3/44/57/...E-1956.jpg

Lawrence.

[pwdrive]

The link for more Schneider schematics from which the one from the previous post was taken:

http://europatubes.over-blog.com/pages/P...00376.html

Lawrence.

[AlanBeckett]

Interesting way of drawing a Schematic.
Any idea what Meter they used because it isn't going to be easy to measure the AGC with those Resistors.

Alan

[boater sam]

Thanks again Lawrence.

I found that one too but on a different site. It is another confusing way of drawing obfuscation.

There would as you say seem to be just AVC, I will have to find out why the tuning eye has no deflection, the caps look terrible. The one I changed showed 19% leakage and twice the capacitance on my China magic box. They are rated at very high voltages eg. 2000v for some odd reason.

The thought has occurred that this is possibly the only set I have worked on this year where the maker still exists.

Merci,
Sam

[boater sam]

May be a Metro nome?

Possibly easier to use a 'scope.

At least the voltages are marked, the HT volts agree. Seems a daft way to draw thing though.

Someone has stuck a patch on the 'speaker cone, or rather a bandage, its a bit of Elastoplast!

[Yorkie]

With regard to the EM34 display, you may find that without a decent external aerial, the signal strength is insufficient for the AGC to operate or give enough voltage swing. I thought I'd got a duff magic eye on a 'Fenman 1' so obtained a new one, to no good effect. I thn made a simple magic eye tester which proved that both the old and new eye were fine. I then connected an external aerial and the magic eye then worked fine in the set.

Good luck with the restoration Sam - assuming that you're still in the Northen Hemisphere! 

If not, I guess this set won't be a 'winter project' but a Spring one.
 

[boater sam]

Still here! leave Friday.  We will still be in the northern hemisphere all winter, just!

Good to get an eye that glows for a change.

Yes, spring projects now, soldering iron cold.

[pwdrive]

Potentiometer, battery and a null indicator, a well known trick for voltage measurement without loading a circuit, would it work for voltages derived from very high resistance circuits such as AGC lines etc...Anyone know or tried it?

Lawrence.

[Terry]

Well, the technique has been known for nearly 175 years, so I assume that someone must have ...

https://en.wikipedia.org/wiki/Potentiome...nstrument)