Universal Output Pentode type Pen26
The valves described in the following section have been designed for use in receivers of the following types:-
(a) 'Universal' receivers which can be operated on either AC or DC mains.
(b) AC mains receivers not employing a power transformer.
(c) Automobile receivers deriving LT supply from the 12V car battery.
Mullard Universal valves are intended to be operated (in Mains receivers) with their heaters connected in series, and with a suitable barretter to maintain the heater current at exactly 0.2 amp.
The number of types has been limited to those representing the most recent practice in valve technique, the principal types being an Octode electron-coupled frequency changer, variable-mu and 'straight' HF pentodes, a double diode for use as detector, and output pentode, with suitable rectifying valves.
An important innovation is the Mullard 'Universal' pin-less base, the valve electrodes being connected to silver-plated side contacts. A suitable form of valve holder is used, having corresponding spring contacts. The advantages of the new form of base include lower capacitative losses, better valve-holder contact, and more compact construction.
The following links lead to a PDF of pages from the original catalogue. FC13 Octode Frequency Changer, VP13A Variable-mu HF Pentode, SP13 HF Pentode, 2D13 Double Diode, Pen26 Output Pentode, UR1 Half Wave Rectifier and UR2 Full Wave Rectifier.
The base described became known in the UK as the Ct8 side contact base. To stabilise the heater current in a series connected heater chain a barretter such as the C1 would be used.