I am tasked with repairing a Chinese manufactured "Line Magnetic" valve amp with a bad channel - it uses 845s and 300Bs. The access to this elephant is from below, and my 1938 RCA valve book categorically states the correct operation of the 845 is socket down, bulb up. I realise filament sag could produce unwanted flashover if this lump was operated on its side but how about upside down?. I have to get in there with meter prods and scope probes. The incumbent tubes are Chinese. Ideas?.
I worked on a Cary 845 some years ago, and I would agree with the RCA book.
I removed the 845 (and all other valves), worked on the circuit, then replaced the valves. I then set up all my measuring equipment connections (bias and HT measurements, scope connections, etc.) and brought it up slowly on a large Variac to confirm that the work was done correctly - while the amplifier was right side up.
I removed the 845 (and all other valves), worked on the circuit, then replaced the valves. I then set up all my measuring equipment connections (bias and HT measurements, scope connections, etc.) and brought it up slowly on a large Variac to confirm that the work was done correctly - while the amplifier was right side up.