Barker Intermediate 88, another restoration job.

[Crackle]

Keep going Sam.
By the way are you back in the UK .
Mike

[boater sam]

Will keep plodding on.

Been back a couple of weeks, it was not easy, thanks.
Sam.

[Mike Watterson]

And yet there is a tuning eye, rather superfluous on an AM set.  Maybe just a sales gimmick?

Originally ONLY AM sets had tuning eyes, because there were no FM sets till later (much later in UK). It was a deluxe feature. A variety of techniques were used before 1934 when RCA invented/developed the CRT based eye
https://www.radiomuseum.org/forum/histor...e_led.html
https://www.radiomuseum.org/forum/magic_...terns.html
https://www.radiomuseum.org/forum/how_th...works.html

Very few Magic Eyes were especially for FM. A few had an extra annunciator for Stereo, but most sets used a lamp and then LEDs were used from 1970s.

Tape recorders used the same ones for AM radios, either the DM70 or EM84 / EM87 types. The DM70 /DM71 battery valve eye was used in more mains radios and mains tape recorders than portable anythings, often with the 1.3V filament supply tapped from an output valve cathode resistor.

The fact is that till the 1960s a magic eye valve was much much cheaper to make than a moving coil meter.
The transistor portable reel to reel and cassette recorder spurred on development of cheap small moving coil meters which were then used in some radios, usually ones with Short wave.

[boater sam]

Of course,  AM eyes were the usual tuning aid but this set is such an anomaly, a cheap cabinet, crudely built, surplus components, a minimum of capacitors and yet its push pull output, has an eye, and a fancy wave flag mechanism. 
The use of valves is not exactly economic either, the double diode 6H6GT has one half used as detector only. 6SL7GT is 1st audio amp and phase inverter for the 2nd output valve.
I have not resolved the AGC voltage yet, there is no delay, and there would appear to be no AGC line decoupling capacitor of any size.

[boater sam]

[Mike Watterson]

If it's just after WWII, then that might have limited the cabinet quality and parts supply. A lot of Octal valves stockpiled for war use, inc magic eyes such as Y63 were cheap 1945 to 1960. Some actually made in USA and relabelled.

Maybe the 0.1uF AGC decoupling cap fell off or they forgot to install it. It might pass QA test without one!

[boater sam]

If it's just after WWII, then that might have limited the cabinet quality and parts supply. A lot of  Octal valves stockpiled for war use, inc magic eyes such as Y63 were cheap 1945 to 1960. Some actually made in USA and relabelled.

Maybe the 0.1uF AGC decoupling cap fell off or they forgot to install it. It might pass QA test without one!

  Can't see one on the circuit diagram of the nearest model I could find with 6V6 output valves, the later model I think. There is a 2000pf ceramic but that's a bit odd for a decoupler on AGC line I would think.

[boater sam]

Definitely  no AGC decoupler capacitor! Never been one either. So nothing to lose, installed a 0.1uf after the 1meg resistor, Makes absolutely no difference. The eye is still always 3/4 closed and closes a bit more with a signal. I'm getting -2.44 volts on a good signal on the grid of the eye, not sure if this is correct, with no signal there is no voltage so what is holding the Y63 eye part closed then?  Its not the eye, i've subbed it.

Found 2 resistors in none critical positions that were well over the  20% tolerance high, shunted them back to value without any change.

[Mike Watterson]

The eye is has a triode driving a "CRT" deflector electrode. The HT/ anode resistor, for a particular grid voltage, will affect the deflection. The Target pin HT has less effect, mostly brightness.
0V = no signal = anode voltage / deflector pin low, maximum shadow
-ve grid enough so anode voltage is high = no shadow. = Strong signal. I'd have thought much more negative than -2.5V.
So check that resistor on preamp anode/ deflector pin hasn't gone high, or HT isn't low.
The eye doesn't open even as much as 1/2 with no signal. It goes about 2/3rds lit, 1/3rd shadow (no signal = 0) to fully lit (preamp cut off).

A video I made:
https://www.youtube.com/watch?v=JhNvdOW2zX4

[boater sam]

Thanks Mike for that.
Reading your reply makes me think that this eye is working correctly, my aerial signal is not high in the workshop. Its only 12 ft of wire nailed to the ceiling inside.
I am more used to the FM sets where the eye is almost wholly shadow with no signal and brightens up almost completely on station.
Sam.