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DMcMahon · 6th Oct 2020, 5:28 pm

Many days back now connected the Series 2 amplifier module to the Series 2 power supply and powered up.

Only valve in the amplifier was the EM 87 magic eye (only powered in Record). HT voltage again was very high around +450 volts. Fitted an EF 86 valve (only spare valve immediately to hand) but still no change to the high HT voltage.

Had to reduce the mains voltage supply to the unit down to around 160 volts by Variac to get the HT output down to around 290 volts, a more comfortable/typical level.

Once I find some donor valves for the other missing valves will fit them and see if any change to the HT voltage. Am hoping that the HT voltage might come down when the output pentode is fitted. I know from some of the old Grundigs that with the output pentode not fitted the HT voltage can be around 100 volts higher than normal, not sure what mechanism causes this, do not think it is current limiting when all valves are fitted.

Will be interesting to see what the Mk. 5 HT voltage is like in comparison.

In the meantime first will check out the grid coupling capacitors.

6th Oct 2020, 5:28 pm	#46
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,603	Re: Brenell Purchases Many days back now connected the Series 2 amplifier module to the Series 2 power supply and powered up. Only valve in the amplifier was the EM 87 magic eye (only powered in Record). HT voltage again was very high around +450 volts. Fitted an EF 86 valve (only spare valve immediately to hand) but still no change to the high HT voltage. Had to reduce the mains voltage supply to the unit down to around 160 volts by Variac to get the HT output down to around 290 volts, a more comfortable/typical level. Once I find some donor valves for the other missing valves will fit them and see if any change to the HT voltage. Am hoping that the HT voltage might come down when the output pentode is fitted. I know from some of the old Grundigs that with the output pentode not fitted the HT voltage can be around 100 volts higher than normal, not sure what mechanism causes this, do not think it is current limiting when all valves are fitted. Will be interesting to see what the Mk. 5 HT voltage is like in comparison. In the meantime first will check out the grid coupling capacitors.