USA Sylvania 6Y6-GA vacuum tubes, original box included, set of 4, believed to be manufactured in the 1950s, long-term storage. The lot number is K4M, but some are faded. These are excellent vacuum tubes that can achieve 6W output in single operation. However, the screen grid voltage is low relative to the plate voltage of 250V, requiring a separate 135V, which necessitates power supply modifications. I only used them for prototyping and then stored them. I have no plans to use them in the future, so I would like to offer them to someone who can utilize them. I have confirmed that current flows through the heater and plate. There are notes on the tubes and original boxes. I have selected a set of 4 from my stock of 15, based on similar plate current values under the manufacturer's standard characteristic conditions. Using an e-tracer, with Vp=Vsg=135V, the Ip was 58-60mA and 47-48mA. The preheating time for the heater was not very long, so there may be significant errors. I will ship via Rakuraku Mercari's anonymous delivery service. These tubes have only been used for short periods of operation for characteristic measurements. However, as they are old, I am selling them as junk items. Please understand that returns are not possible for any issues, except for problems caused by damage to the packaging upon arrival. - Brand: USA Sylvania - Model: 6Y6GA - Original box included, set of 4 I am listing many 6Y6 tubes. Discounts are available for combined shipping. Thank you for looking.