• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6V6 housing material

Metal receiving tubes use a steel shell without plating. Any particular alloy content is inconsequential to the operation of the tubes and varied by manufacturer. It is enough to say that the metal's carbon content is low enough to classify as "steel" (i.e. <0.8%) and the alloys used provide workability such that they are ductile enough to allow the shell to be drawn to shape and properly sealed.
 
Industrial application?

Sounds like it might be related to the Material Safety Data Sheet?
There is the paint on the outside. Perhaps there is primer underneath the paint.
The real issue might be all the various toxic materials inside, underneath the metal shell.
 
Most metal tubes were uncoated on the inside and painted black on the outside. The metal itself was described as "steel" or "mild steel" in literature from the 1930's when RCA first introduced the metal tubes. The metal is magnetic and can be magnetized which can potentially affect operation.

There were references in literature about the fact that the metal can must be kept at a potential less than the cathode to avoid electron flow from the cathode to the can. In most cases the can was connected to pin 1 of the octal base and usually grounded since the can was often used as the shield in a radio application. The metal 6V6 tubes that I have do have the can connected to pin 1.

Many amps and old radios were designed for the 6V6GT (glass) and pin 1 was left floating. In some cases the socket itself did not even have a receptacle for pin 1. A metal 6V6 will work fine in these devices but an electrical charge can build up on the metal can. Due to its small size the zap from discharging this can barely be felt if your finger does the discharging. Random discharges through the dust and dirt often found in an old radio can result in static in AM reception.

Some metal tubes were coated internally so that electron flow from the cathode to the shell did not happen. I have not taken any metal tubes apart since my high school electronics class (1967 - 1970) so I don't remember the details. Whatever it was it looked brown and shiny.

The teacher bet me that I could not make the outer metal shell glow red on a metal 6L6. I won that bet and stunk up the whole vocational wing of the school as the phenolic base burned after the red glow and peeling paint had commenced.
 
Great info, and much appreciated. An era that was just a bit before my time!

I was thinking there may have been some consideration within the metal for the potential oxide layer where any glass layer would seal to it.

I may have some other types here to analyze and get some clues.
 
Thanks, that’s going to save me having to disect my single original RCA 6F6 that I have here to verify that construction where the glass is mated to the shell.

I will spill the beans when the project is complete, it isn’t audio related btw…
 
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