This exhibit has lost most of its identification. What remains is CBL.1.57 which is probably a batch of CBL1's.

The CBL1 is a double diode output pentode. The aim of this high mutual conductance valve was to reduce the number of devices in wireless receivers. The CBL1 has a 200 mA heater requirement for heater chain use in receivers without mains transformers. The diodes would demodulate the signal and generate AGC and the resultant audio would drive the output stage directly. This implies strong signals to derive the drive voltage. It is safe to say that this valve was aimed directly at the low cost local station receiver market. The CBL31 was electrically identical but on an IO base. The design probably dates from the mid to late 1930s. The CL4 is virtually the output pentode section of the CBL1 in stand alone form. The EBL1 takes the same high gain idea and translates it for the higher voltages available in receivers with mains transformers.

The internal and external coatings together with the silvering from firing the getter all conspire to obscure the electrodes. The cement holding the glass in the base has given way and the valve has been taped up with fabric insulation tape. In the Tungsram CBL1 the manufacturer has placed a shrink wrap sleeve over the valve to keep the two parts together.

The cathode resistor is specified as 167 Ohms, the output load as 4,500 Ohms and under these conditions an output of 4 Watts at 10% total distortion is possible.

The classic envelope is 44 mm in diameter and, excluding the Ct8 base pins, is 128 mm tall.

 
Pin Connections

Ct8	1	2	3	4	5	6	7	8	tc
	m	h	h	k	a(d1)	a(d2)	-	a	g1

 
Absolute Maximum Operating Conditions

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm
	44.0	0.2	200	200	-8.5	45.0	6.0	35,000	8.0

Thanks to Frank Philipse for supplying the above datasheet

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This exhibit was last updated on 03 January 2008 {find valves by name}