Pye 'Fenman 1' magic eye puzzler

[Yorkie]

Late in 2011, the restoration of a Pye Fenman which I referred to in this link stalled, as is too often the case with me, basically, because I'm a bit unfocused and easily distracted when other things crop up, and my priorites change, so half-finished projects go into hibernation, sometimes for years. Ludicrous, I know:

http://golbornevintageradio.org/forum/sh...p?tid=1473&highlight=Pye+Fenman+1

I completed the electronics, replaced the ECC85 and fitted an NOS EM80 magic eye. All seemd to be well - working fine on FM and AM, and the magic eye did its stuff, so I put the chassis to one side and set about stripping the old gunge off the cabinet to polish it. Then the winter of 2011 came and the weather wasn't conducive to French polshing, which I thought I'd try my hand at.

Then summer 2012 came, and before I knew it, it was autumn again, but I made a bit of an effort on the cabinet, though wasn't happy with the result, so again the cabinet was put to one side and forgotten about. I'm trying to make an effort to reduce the number of sets I have and this is one that has to go. Hence, I recently fished the cabinet out agan, and furtled with it to a point at which I'm content with it.

Tried the radio - all working fine, so I installed the chassis in the cabinet including the magic eye, which is on a separate little sub assembly. No sign of life from the EM80.

The few components associated with the EM80 seem to be in order, including the anode load resistor and the HT voltage correct (220V). I'm not very clued up with magic eyes, (or checking the funcion of AGC for that matter), but as I understand it, as the AGC goes more negative on the grid of the EM80, the voltage on the triode anode goes more positive, changing the display.

The AGC seems to be working OK, in that the voltage varies (around a Volt), when strong signals are tuned in, but I assume that even if the AGC isn't working exactly as it should there ought at least to be some signs of life - a green flourescent in the EM80, yet there's nothing at all - not even a glimmer.

Not really my choice of music, but here's an example of an EM80 working as it should:

EM80 Display: http://www.youtube.com/watch?v=3062ud_PWC4

I mentioned in another thread that I've ordered an NOS EM80 rather than keep looking for what might be a non-existant fault, but meanwhile, I found an interesting and simple EM80 test circuit which I might knock up, which I've attached. I assume that the voltage shown on the 470K resistor to the grid is from minus 2V to zero. Presumably I could just switch in and out a 1.5V battery with negative to the 470k and positive to ground to enable the display to open and close?

To summarise, even if there's a fault on the AGC side - and I don't think there is - should I see at least a green flourescent glow from the EM80 if the heater is fine and the HT correct?

Any thoughts anyone please?

[ed731pdh]

I'm wondering if it's gone soft over the winter. Your test circuit should help.

[Yorkie]

I'm wondering if it's gone soft over the winter.

Or maybe I have!!

Thanks for reading my post - I'll report on progress with the little test circuit in due course.

[pwdrive]

Hello David if there is no green display it usually indicates a failed valve, the usual checks will confirm....

Heaters lit up.
Target anode volts present on valve pin.
Cathode pin connected to HT -Ve.
Triode anode pin voltage present.

If bright green display but no tuning indication....

Triode anode volts present on valve pin (usually via a high resistance source) and varying between no signal and strong signal.
Ditto triode grid.

Dull display normally means a duff valve if heaters/HT etc are present on the pins.

Lawrence.

[Refugee]

I would say that since it has been stored for some time the valve pins could have got tarnished and giving them a good clean may do the trick.

[Yorkie]

Thanks guys, for reading my post and your helpful input.

I will build the little tester if only out of curiousity, but hopefully, when my NOS valves arrive in a couple of weeks or so, that will prove that this valve is duff - as dead as Mony Python parrot.

[pwdrive]

If all else fails you could muck about with this idea:

https://www.youtube.com/watch?v=QFTDOZz-LlE

Lawrence.

[Steve_P]

Magic Eye Problems.

Heater not lit - Either Heater O/C, bad heater wiring, dirt on pins or faulty socket.
Heater Lit - No Display at All : Check HT, Screen Voltage and Cathode voltage. Also R38 on the trader sheet.
Heater Lit, Display Dim - Might be the valve. If the voltages are OK, try upping them to give a tired valve a chance. When you get a new valve, remember you did this...
Heater Lit, Display all the way over - check the resistor in the target volts chain (R37 on the trader sheet).
Heater lit, display OK but does very little - In the Pye Fenman 1, check R30 and C60 if the AGC line is OK.

Cheers,

Steve P.

A quick check is to fit an EM84, Common tape recorder valve and a recognised mod at the time!

[Joe]

If all else fails you could muck about with this idea:

https://www.youtube.com/watch?v=QFTDOZz-LlE

Lawrence.

I must confess to having ideas involving barograph drivers and LEDs myself.

Thankfully most of my radios don't have them. I can hear when they are tuned in properly and they just strike me as a needless complication waiting to go wrong.

- Joe

[Yorkie]

Thanks for your helpful tips Steve. I'm coming to the conclusion that it is the valve that's at fault, despite it being an NOS valve some months back, which worked OK when fitted. The heaters are intact and the valve warms up, all the voltages appear correct, and R37 & 38 are fine. C60 was replaced along with all other waxies, but there's not the faintest glimmer from the display.

I'll get on and build the little tester to see what that reveals!