I don't think any are used in the vertical amplifiers of either the 547 or 556 (which are nearly identical designs BTW), as these are all transistorized, except the first stage cathode follower which is a 12AT7. The other tubes in the 547 are all single and dual sided tubes commonly used in several Tek scopes.


The 556 uses two 6M11 triple triodes, one in each sweep generator.

There is a novel miller integrator sweep generator design which can be implemented as a one tube design using a combination pentode-triode tube. The Miller integrator itself is named a "Phastastitron" short for fantastic. This cleaver design uses a single pentode for all of the functions of the sweep generator, including the cut off diodes and synchronization (rather than triggered operation.) The screens are used as additional grids in this design. The triode serves as a cathode follower, to prevent the external load from altering the timing linearity. Tek never used this design, as all Tek scopes have triggered rather than synchronized to the input signal. It is useful if you want to design one of those “three tube scopes”.

- Steve