6BQ7A Dual Triode

[darkspeed]

The 6BQ7A is an all glass miniature VHF double triode and is internally screened.
A valve like this would be used for RF amplification, or frequency multiplication. In the latter case the valve is operated as a non liner amplifier. This causes harmonics of the signal frequency to appear in the anode current. The anode tuned circuit is then chosen to resonate at one of the harmonics, usually the second or third.
The thin glass tube envelope is 19 mm in diameter and excluding the B9A base pins the valve is 49 mm long.

[the_big_m_in_ok]

Guitar amplifier builder/designers are increasingly turning to vacuum tubes for sound fidelity in amplification.  So, tube manufacturers are providing a market to these electronic engineers by improving certain existing designs that served well in decades-old amplifier applications.

'Web sites like these cater to the demand:

http://thetubestore.com/

http://wireless.ee.washington.edu/indep_study/ben2.pdf

I admit there's one catch:
These designs are quite possibly optimized for the human auditory range to amplify signals.    Typical radio frequencies would be outside the range of ordinary hearing.
On the positive side:
New tubes are being deliberately manufactured for a ready market of engineering enthusiasts and radio frequency tubes aren't being built for lack of a market.  Used tubes are about all that's left on the retail level of business.  But, then, there's the 'flea market' scene; and "you takes your chances", as it were, with that road.

--Lee

[darkspeed]

more specs and it also has a ac or dc heater