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Old 25th Feb 2020, 10:53 pm   #194
DMcMahon
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Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Grundig TK 819 Any Useful Info

Even though not currently important, I decided to check out more the abnormal high voltage on the anode of the EF 86 valve and the apparent low brightness of the EF 86.

Remeasured the heater supply voltage at the pins of the EF 86, as measured before it is still 6.3 volts AC. The anode is still around 200vdc, the voltage at the HT side of the anode resistor R8 (200k) is around 202 volts, so only a couple of volts being dropped across R8 so another indicator I think that the valve is not conducting much. Wanted to measure the cathode (should be grounded) and the Screen Grid (G2) of the EF 86 (should be around 30 volts) as these if bad would impact any valve conduction, but impossible to see the valve pins let alone get to them to measure them.

Due to the fact that EF 804 valve base is surrounded and partially covered by the larger valve base adaptor (to adapt the wiring to suit the alternative EF 86) then half of the valve base area is covered by the microphone transformer, it makes it impossible to see/get to some of the valve pins. So only way to practically fully check all the valve base wiring and measure all the pins is to temporarily remove the microphone transformer which is a bit of pain, as its insulated mounting plates are riveted to the side panel, so will have to drill the rivets out.

On my TK 5 I checked the brightness of the EF 86 and like TK 819 it was not overly bright and swapping the EF 86's between the 2 units gave as good the same brightness levels in both units. So I think now that the low level brightness of the EF 86 is probably not abnormal, with the room lights off could see the lit up valve fairly well. With the EF 86 from the TK 5 fitted into the TK 819 got the same 200 volts anode voltage, so I think the high anode voltage/assumed lack of conduction is not due to the EF 86 valve itself having a problem.
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