Fixing an EM80 Magic Eye - UK Vintage Radio Repair and Restoration Discussion Forum

coopzone · 30th Jan 2018, 6:29 pm

I acquired an ekco A274 last week. Every since I have been looking for a replacement EM80 valve. But no longer!

I was surprised at the price of EM80's (at £15.00), so I investigated it a bit further. I noticed that the anode resister (470k) appeared to have 0volt on pin 7 of the EM80. I measured it's value and it was ok. Next I removed the EM80 and checked pin 7 again (on the socket) and bingo 250V.

So I checked the resistance from pin 7 to all the other pins on the valve - only to find a dead short to pin 2 (cathode). So it looks like I need a new EM80 after all.

Then I thought, maybe it's some sort of loose metal debre possibly a bit of grid degraded over the years, so I thought what the hell. It's broke anyway I'll give it a good shake and thump!

After this I tested pin 7 again and hey presto - no more short!

Tested it it back in the radio and it works a treat. See photo

Anyone else had this sort of experience ?

coop zone

Nuvistor · 30th Jan 2018, 6:35 pm

Intermittent valves were common enough when I was fixing radios etc, so not unusual. Just how long it will last is unknown, have see how well it lasts.

paulsherwin · 30th Jan 2018, 6:53 pm

It's always worth giving them a tap and a shake if there's an internal short. Occasionally you get lucky, and there's nothing to lose.

Graham G3ZVT · 30th Jan 2018, 8:16 pm

I once repaired a CRT from an old oscilloscope with an O/C heater by applying current-limited high voltage across the heater pins. It worked, but only lasted a few weeks.

Sideband · 30th Jan 2018, 9:46 pm

I had a DK32 battery mixer valve supposedly brand new that had a dead short from screen grid to anode. With nothing to lose, I applied 50V DC from a current limited supply across the shorted pins. There was a flash inside the valve and when I checked, the short had gone. What's more, the valve then worked perfectly and continues to do so...something like 10 years now.

David G4EBT · 30th Jan 2018, 10:37 pm

Quote:

Originally Posted by coopzone

I acquired an ekco A274 last week. Every since I have been looking for a replacement EM80 valve. But no longer!

I was surprised at the price of EM80's (at £15.00), so I investigated it a bit further.

If you do need an EM80 they're one of the few magic eyes that are very plentiful and typically cost around £5.00 new, plus about £5.00 post from Russia. I've had several and they're excellent. They're also known as '6BR5'/6EP1. The only slight issue with them is that the 'bottle' is about 1mm larger in diameter. In most cases that won't matter, but in one set I restored, the EM80 was fitted in a shroud into which the new one wouldn't quite fit. I just made a new shroud from hardwood.

Should you end up needing one, here's where I got mine from:

https://www.ebay.co.uk/itm/Russian-M...75.c100623.m-1

In one instance I was led a merry dance thinking that the eye or the circuitry was faulty, when in fact what was causing the eye to be sluggish was that on an internal frame aerial even when signals were received at seemingly good strength, the AVC voltage didn't go negative sufficiently to operate the eye. When I plugged in an external aerial, the eye worked fine.

Hope that helps.

Every success with the set.

Singlofty · 1st Feb 2018, 9:25 am

The Russian replacements that I purchased are also 5 or 6 mm longer than the originals and wouldn't fit into a Regentone A155 as the socket fouled the dial cord. Coincidentally I've just fitted one to an Ecko A274 but can't get the agc voltage above -0.5v so it won't respond. Not sure if this isn't just down to signal strength though.
Dave

David G4EBT · 1st Feb 2018, 7:38 pm

When I restored a Pye 'Fenman 1' some time ago, the EM80 display didn't vary, even on what appeared to be quite strong signals. I tried a new Russian one, with no improvement, so I built a little tester to enable me to vary the negative voltage on the grid;- eg, 0V, -1.5V, - 3V etc. The original eye worked fine as did the new one. Then it dawned on me that the AGC voltage wasn't going sufficiently negative when relying on the internal aerial. As soon as I attached an external aerial, the eye became very lively.

Similarly, when I restored a Unitra Figaro Special, which uses a DM70 'exclamation mark' magic eye, on the 'Figaro' internal ferrite rod, off tune the AGC voltage on the grid of the DM70 was -0.45V, but with what seemed to be a strong signal tuned in, it only went to -0.75V. However, when I attached an external aerial, the AGC Voltage would go as much as -9V negative and the exclamation mark would shrink to just the dot.

I've attached a sketch of the circuit and pics of the EM80 tester that I made, and the broken shroud from the Fenam 1, caused by my trying to fit the slightly larger new Russian eye, alongside the new shroud I made. I sprayed the shroud gold before fitting. The third pic shows the EM80 display with 0V on the grid. To get the 'angel wings' to open wide, took about -4.5V.

Hope that's of interest.

30th Jan 2018, 6:29 pm	#1
coopzone Hexode Join Date: Jan 2018 Location: Cannock, Staffordshire, UK. Posts: 268	Fixing an EM80 Magic Eye I acquired an ekco A274 last week. Every since I have been looking for a replacement EM80 valve. But no longer! I was surprised at the price of EM80's (at £15.00), so I investigated it a bit further. I noticed that the anode resister (470k) appeared to have 0volt on pin 7 of the EM80. I measured it's value and it was ok. Next I removed the EM80 and checked pin 7 again (on the socket) and bingo 250V. So I checked the resistance from pin 7 to all the other pins on the valve - only to find a dead short to pin 2 (cathode). So it looks like I need a new EM80 after all. Then I thought, maybe it's some sort of loose metal debre possibly a bit of grid degraded over the years, so I thought what the hell. It's broke anyway I'll give it a good shake and thump! After this I tested pin 7 again and hey presto - no more short! Tested it it back in the radio and it works a treat. See photo Anyone else had this sort of experience ? coop zone Attached Thumbnails

30th Jan 2018, 6:35 pm	#2
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Fixing an EM80 Magic Eye Intermittent valves were common enough when I was fixing radios etc, so not unusual. Just how long it will last is unknown, have see how well it lasts. __________________ Frank

30th Jan 2018, 6:53 pm	#3
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,943	Re: Fixing an EM80 Magic Eye It's always worth giving them a tap and a shake if there's an internal short. Occasionally you get lucky, and there's nothing to lose.

30th Jan 2018, 8:16 pm	#4
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,713	Re: Fixing an EM80 Magic Eye I once repaired a CRT from an old oscilloscope with an O/C heater by applying current-limited high voltage across the heater pins. It worked, but only lasted a few weeks. __________________ -- Graham. G3ZVT

30th Jan 2018, 9:46 pm	#5
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,571	Re: Fixing an EM80 Magic Eye I had a DK32 battery mixer valve supposedly brand new that had a dead short from screen grid to anode. With nothing to lose, I applied 50V DC from a current limited supply across the shorted pins. There was a flash inside the valve and when I checked, the short had gone. What's more, the valve then worked perfectly and continues to do so...something like 10 years now. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

1st Feb 2018, 9:25 am	#7
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Re: Fixing an EM80 Magic Eye The Russian replacements that I purchased are also 5 or 6 mm longer than the originals and wouldn't fit into a Regentone A155 as the socket fouled the dial cord. Coincidentally I've just fitted one to an Ecko A274 but can't get the agc voltage above -0.5v so it won't respond. Not sure if this isn't just down to signal strength though. Dave

1st Feb 2018, 7:38 pm	#8
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,761	Re: Fixing an EM80 Magic Eye When I restored a Pye 'Fenman 1' some time ago, the EM80 display didn't vary, even on what appeared to be quite strong signals. I tried a new Russian one, with no improvement, so I built a little tester to enable me to vary the negative voltage on the grid;- eg, 0V, -1.5V, - 3V etc. The original eye worked fine as did the new one. Then it dawned on me that the AGC voltage wasn't going sufficiently negative when relying on the internal aerial. As soon as I attached an external aerial, the eye became very lively. Similarly, when I restored a Unitra Figaro Special, which uses a DM70 'exclamation mark' magic eye, on the 'Figaro' internal ferrite rod, off tune the AGC voltage on the grid of the DM70 was -0.45V, but with what seemed to be a strong signal tuned in, it only went to -0.75V. However, when I attached an external aerial, the AGC Voltage would go as much as -9V negative and the exclamation mark would shrink to just the dot. I've attached a sketch of the circuit and pics of the EM80 tester that I made, and the broken shroud from the Fenam 1, caused by my trying to fit the slightly larger new Russian eye, alongside the new shroud I made. I sprayed the shroud gold before fitting. The third pic shows the EM80 display with 0V on the grid. To get the 'angel wings' to open wide, took about -4.5V. Hope that's of interest. Attached Thumbnails __________________ David. BVWS Member. G-QRP Club member 1339.