Magic Eye! - UK Vintage Radio Repair and Restoration Discussion Forum

Roger13 · 7th Nov 2009, 6:56 pm

Hi folks.

I'm busy re-hashing an old Ultra 6202 recorder and everything works fine except the 'magic eye' valve.

Rather than giving a nice clean double light, it is glowing dully along the full length. Replacing it with another EM87 simply reproduces the same effect. This would suggest to me that the problem lies further back in the chain, although I cannot rule out the possibility that I have two duff valves!

Any ideas would be most gratefully received.

Cheers,

Roger.

paulsherwin · 7th Nov 2009, 7:07 pm

Magic eyes are just voltage indicators. You can test the deflection by putting some DC volts on the grid, say from a PP3.

I agree, it's unlikely that two valves have identical faults.

Paul

Sideband · 7th Nov 2009, 8:42 pm

Most magic eyes have high value resistors in the target and anode supplies...typically 470K or even 1 meg. Either or both of these could be high or open circuit. Just change them and see if it makes any difference to the brightness.

Rich.

AndiiT · 7th Nov 2009, 11:36 pm

Hi,
If this is the model that I suspect it may be check R24 (100R - that's the value that is shown on my "equivalent" Ferguson diagram, but as others have said the value may differ) which connects to pins 7 and 9 of the EM87 "Magic Eye" I have had this resistor go high in value and cause the symptoms that you are experiencing.

Regards
Andrew

kalee20 · 8th Nov 2009, 12:04 am

Quote:

Originally Posted by Richard_Newman

Most magic eyes have high value resistors in the target and anode supplies...typically 470K or even 1 meg.

In the anode supply, yes - because it's the anode load, so that the anode voltage can respond to the grid voltage. But not in the target, which is connected straight up to HT+.

Roger13 · 8th Nov 2009, 9:33 am

Hi.

Thanks for the info. Most has gone straight over my head but my tame engineer friend will now have a pointer in the right direction.

Many thanks.

Roger.

PS: I just love these little machines. This particular one is identical to my first ever recorder, bought with my first month's wages when I started work (with a little help from my dad....). Pity it's not in quite such good condition though.

Sideband · 8th Nov 2009, 10:54 pm

Quote:

Originally Posted by kalee20

Quote:

Originally Posted by Richard_Newman

Most magic eyes have high value resistors in the target and anode supplies...typically 470K or even 1 meg.

In the anode supply, yes - because it's the anode load, so that the anode voltage can respond to the grid voltage. But not in the target, which is connected straight up to HT+.

Yes I stand corrected on this

.

Rich.

7th Nov 2009, 6:56 pm	#1
Roger13 Retired Dormant Member Join Date: Jun 2006 Location: Wrentham, Suffolk, UK. Posts: 508	Magic Eye! Hi folks. I'm busy re-hashing an old Ultra 6202 recorder and everything works fine except the 'magic eye' valve. Rather than giving a nice clean double light, it is glowing dully along the full length. Replacing it with another EM87 simply reproduces the same effect. This would suggest to me that the problem lies further back in the chain, although I cannot rule out the possibility that I have two duff valves! Any ideas would be most gratefully received. Cheers, Roger.

7th Nov 2009, 7:07 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,934	Re: Magic Eye! Magic eyes are just voltage indicators. You can test the deflection by putting some DC volts on the grid, say from a PP3. I agree, it's unlikely that two valves have identical faults. Paul

7th Nov 2009, 8:42 pm	#3
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,567	Re: Magic Eye! Most magic eyes have high value resistors in the target and anode supplies...typically 470K or even 1 meg. Either or both of these could be high or open circuit. Just change them and see if it makes any difference to the brightness. Rich. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

7th Nov 2009, 11:36 pm	#4
AndiiT Octode Join Date: Aug 2005 Location: Saltburn-East, Cleveland, UK. Posts: 1,786	Re: Magic Eye! Hi, If this is the model that I suspect it may be check R24 (100R - that's the value that is shown on my "equivalent" Ferguson diagram, but as others have said the value may differ) which connects to pins 7 and 9 of the EM87 "Magic Eye" I have had this resistor go high in value and cause the symptoms that you are experiencing. Regards Andrew

8th Nov 2009, 9:33 am	#6
Roger13 Retired Dormant Member Join Date: Jun 2006 Location: Wrentham, Suffolk, UK. Posts: 508	Re: Magic Eye! Hi. Thanks for the info. Most has gone straight over my head but my tame engineer friend will now have a pointer in the right direction. Many thanks. Roger. PS: I just love these little machines. This particular one is identical to my first ever recorder, bought with my first month's wages when I started work (with a little help from my dad....). Pity it's not in quite such good condition though.