Barker Intermediate 88, another restoration job.

[Mike Watterson]

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.

Different kind of eye. Still though about 1/3 lit with no signal. The EM34 and some others went down to less than 1/2 lit probably due to having more deflection electrodes, but the Y63 is basically an older design similar to the original RCA eye. I suspect most used in the 1950s were war surplus made for the R1155 or similar applications, not sure. Certainly a few 1950s testers used them as null meters in bridges/capacitor meters.

[boater sam]

Taking advice on board, I checked the HT voltages, all a bit low. Rectifier is not too bad, I am reluctant to use solid state diodes anyway due to the instant high HT that they give.
There are 3 smoothing resistors, first was within 20%, second and third outside spec. I have shunted them back to what is probably much nearer to the desired value than the originals were, the HT is better.
The eye still opens and closes the same amount and I can't see how to get the designed maximum grid voltage swing of 22v on the AGC line to give complete range. Taking Mike's description it is probably as designed, i.e. two thirds lit with no signal and closing to almost completely lit with around 3v AGC.
Difficult to describe accurately, I am saying eye open when not lit, eye closed when completely green lit. That is probably logically backwards!
It is a little brighter though. Reception is just the same, a little insensitive on the top frequencies of the medium wave as to be expected with a poor aerial and small transmitters.
I was going to do something with the cabinet but its cold and wet today and I have had 2 duff Karcher power washes dumped on me for repairs, the workshop is badly crowded too. Really must part with some sets, there are over 100 in there now.

[Mike Watterson]

0 on AGC is no signal, eye largest dark. Reduce the anode resistor if the eye isn't fully open (not much more than 1/3 dark on a Y63).
AGC goes negative as signal is stronger. Once there is no dark, fully lit, a more negative AGC voltage won't do much on the eyes, though some will overlap.
Check leakage of capacitors across HT. One simple way with a parallel heater supply is remove all valves except the rectifier:
1) Measure and write down all series resistors in HT rail with power off.
2) Measure HT at rectifier cathode, first HT cap. Calculate what the other voltages should be.
3) Measure voltage across each capacitor. If it is lower than expected the capacitor is leaky.

Note that ANY leaky screen grid capacitors can dramatically lower the gain. The G2 can be used to vary gain over a 5:1 range for some valves. It's rarely done, though the so called RF gain on my Hallicrafters S72 actually varies IF and RF gain by adjusting the g2 volts on the 1T4 valves. Unlike g1 AGC, it does work on most Pentodes, not just variable mu / remote cut off types with the progressive wound g1 grid wire.

It could be that the Barker 88 is now working as well as can be expected.

I also doubt I've often seen AGC go as far as -6V. You can easily have more than -20V on an FM detector!

A very few valve sets have a slight negative bias for no signal. A car radio with the 13.6V HT may have +1 volts for no signal and certainly operates the ECH83 (if there is no inverter or vibrator, but about +12V anode) at about +1v, it's really just a rebranded ECH81. Such sets always had a pair of Germanium power transistors for audio, you need at least 80V from a vibrator or inverter for enough audio from valves on a car loudspeaker. A small portable can be only 45V HT, though won't be loud!