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Chris Parry · 26th Dec 2011, 11:05 am

6CH6: Not automatically "special quality". Brimar was owned by STC and in the nomenclature used by this company, special quality was called "Trustworthy". Those valves had a dagger-shaped yellow triangular paper "T" adhesive, which in later production became part of the white printing. The "T" valves were graded for survival under conditions of shock, bump & vibration. But very often, the cathodes of the "T" valves were no better than commercial grade - because they did not need to be.

Some 6CH6s carried the "T" label if they had been procured for arduous service. However, all STC & Brimar 6CH6s without exception, were suitable for "professional" service. This meant very long and stable continuous operation in benign environment such as telephone exchanges, fixed transmitter sites and broadcasting studios. All of the "professional" valves had excellent cathodes. Thus if you can find a STC or Brimar 6CH6 with the "T" logo on it, there you have a very fine valve indeed which will last for ages.

It's worth pointing out that the 6CH6 was also made by other manufacturers. The Mullard EL821s were also very good indeed, but many of the USA 6CH6s are no better than ordinary commercial grade.

Chris.

26th Dec 2011, 11:05 am	#139
Chris Parry Retired Dormant Member Join Date: Jun 2011 Location: Waterlooville, Hampshire, UK. Posts: 237	Re: Valve Questions 6CH6: Not automatically "special quality". Brimar was owned by STC and in the nomenclature used by this company, special quality was called "Trustworthy". Those valves had a dagger-shaped yellow triangular paper "T" adhesive, which in later production became part of the white printing. The "T" valves were graded for survival under conditions of shock, bump & vibration. But very often, the cathodes of the "T" valves were no better than commercial grade - because they did not need to be. Some 6CH6s carried the "T" label if they had been procured for arduous service. However, all STC & Brimar 6CH6s without exception, were suitable for "professional" service. This meant very long and stable continuous operation in benign environment such as telephone exchanges, fixed transmitter sites and broadcasting studios. All of the "professional" valves had excellent cathodes. Thus if you can find a STC or Brimar 6CH6 with the "T" logo on it, there you have a very fine valve indeed which will last for ages. It's worth pointing out that the 6CH6 was also made by other manufacturers. The Mullard EL821s were also very good indeed, but many of the USA 6CH6s are no better than ordinary commercial grade. Chris.