UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - EHT warm-up delay in pre-war sets

FERNSEH · 14th Sep 2017, 9:56 pm

Employ an ST&C DLS10 delay switch to hold the EHT off until all the timebase valves are fully warmed up.
Some time ago I modified an HMV 801 radiogram to employ a pair of triode connected KT66 tetrodes to replace the hard to find PX25 triodes. A DLS10 was used to delay the HT supply until the indirectly heated output valves had warmed up.
The Marconi-Osram EHT rectifiers have directly heated cathodes. The Mazda U21 and U22 EHT rectifiers have slow warm up indirectly heated cathodes.

http://www.radiomuseum.org/tubes/tube_u17.html

DFWB.

14th Sep 2017, 9:56 pm	#16
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: EHT warm-up delay in pre-war sets Employ an ST&C DLS10 delay switch to hold the EHT off until all the timebase valves are fully warmed up. Some time ago I modified an HMV 801 radiogram to employ a pair of triode connected KT66 tetrodes to replace the hard to find PX25 triodes. A DLS10 was used to delay the HT supply until the indirectly heated output valves had warmed up. The Marconi-Osram EHT rectifiers have directly heated cathodes. The Mazda U21 and U22 EHT rectifiers have slow warm up indirectly heated cathodes. http://www.radiomuseum.org/tubes/tube_u17.html DFWB.