Grundig 2012 intermittent volume.

[pilot mariner]

Mmm difficult to say Alan, it looks original so could have been done very well, or a very long time ago. I will check the pinouts, or do you know off hand if I could plug an ef41 in to try without damage?
Going back to the fault, I am measuring 104 volts on the EC92 anode. This is after a mains transformer change and conversion to silicon diodes.

Mark

[AlanBeckett]

Pins 3 and 4 are the problem. They are marked as Internal Connections on EF41. Some Manufacturers were brave enough to use them as 'Alternative' Connections, but it's not to be recommended, particularly if Valves come from different manufacturers.
On EAF42 Pin 3 is the Diode Anode and Pin 4 is G3 - Suppressor. If there's no connection to Pin 4 then I would guess it should be an EF41, but not certainly. Manufacturers of that era often substituted similar Valves if they couldn't get enough of the usual ones.

That Supply to the EC92 looks OK from the Data Sheet. What are the other Voltages like?

http://www.r-type.org/exhib/aai0173.htm

Alan

[pilot mariner]

There are no connections on pins 3 and 4 of the EAF42.

EC92 voltages are
1. 144V
2. 0V
3. 6.8V ac
4. 0V
5. 0V
6. 7.5V

Mark.

[AlanBeckett]

That means G3 is Floating. I suspect it should be an EF41
The Voltages on the EC92 look OK although the Heater Voltage is a tad high.

Alan

[pilot mariner]

In post 6 I think I was jumping to conclusions too readily in condemning the EC92, the scanner signal seems constant (but reduced) when pulling valves further down the chain. The fault seems only to occur when all valves are fitted. Maybe the scanner idea is not such a good one after all, as it picks up radiation from the whole IF chain, not just the tuner box as proved above.

Mark

[pwdrive]

http://www.doctsf.com/documents/afficher_document.php?num_doc=36735&num_fic=1

(Posted on UKVRR also)

Lawrence

[pilot mariner]

Thankyou very much Lawrence (also posted on UKVRR)

Mark

[pilot mariner]

The fault was eventually traced to a faulty 25pf polystyrene capacitor in one of the IFT cans.
Many thanks to all who helped.

[pwdrive]

They used to give trouble in TV line time bases not long after they were new back in the day.

Lawrence.

[AlanBeckett]

Interesting. I never had any problems with Suflex but probably not at those sort of Voltages.

Did you change the EAF42 for an EF41?

Alan