Rod and tube resistors

VR Rod and Tube Resistors are manufactured from a carefully selected mixture of clays, alumina and carbon. After blending, the material is extruded into the required shape and then fired, in a controlled atmosphere, at high temperature.

Aluminium is then flame sprayed onto the barrel surfaces (as standard)  to provide electrical contact.

Alternative metallised contacts and corona shielded terminals are also available.

Rod and Tube Resistors are available with Outside Diameters ranging from 10mm to 50mm and in Lengths up to 600mm.

With High Surge Energy Rating and Low Inductance, typical applications for HVR Rod and Tube Resistors include  Dummy Aerial Loads, Overvoltage Protection, Capacitor Discharge and Anti Parasitic Elements in the grid and anode circuits of power valves in induction heaters.

TYPEDo (mm)Di (mm)L (mm)Lm NOM.  (mm)WEIGHT (g)OHMS MinOHMS MaxJOULES @ 20˚CWATTS @ 20˚CIMPULSE VOLTS (1.2 / 50 µs)
71025154602529547100004500015012 Log R
70125152502516022470022000908 log R
7022515150259510220011000556 Log R
708*20-60-2001038-1304r74700-18-803.3 Log R to 7.5 Log R
721*10-50-1501007-23103300-10-301.6 Log R to 5 Log R
72010-11610182222002600204.3 Log R
71910-561091010001100101.9 Log R
72310-501071010001000101.6 Log


At other ambients, Ta °C, Watts and Joules must be multiplied by the factor (220 – Ta) / 200.

* Types 708 and 721 are available in custom lengths.

Also Available:

50mm Diameter Tubes offering Higher Energy Absorption / Higher Average Power Rating.

25mm Diameter Tubes manufactured to custom lengths.

25mm Diameter Tubes assembled with Aluminium Ferrule Terminals.


Electrical Contacts

The standard electrical contacts are aluminium metallised surfaces.

Alternative metallised contacts are available in silver, brass, copper or nickel.

Corona shielded terminals are available.

Radial wire terminations are available on 10mm diameter rods.

Note :

Types 708 and 721 are available to customised lengths within the limits shown.

Custom length tubes (Do = 25mm, Di = 15mm) and larger Diamater Tubes (Do = 50mm) are also available.


Resistance Values

Preferred values are to the E6 series per decade. Other resistance values may be made available upon request.

Resistance Tolerance

± 20% but ± 10% may be made available.

Temperature Coefficient – TCR

Between – 0.8% and – 0.16% per °C rise in temperature. The higher the resistivity, the higher the temperature coefficient.

Shelf Life

After 6 months storage under normal conditions the resistance change is less than ± 3%.

Load Life Stability

After 2000 hours continuous load producing 220 °C surface temperature, the resistance change is less than ± 20%.


This is negligible and the resistors may be described as Non-Inductive. In practice, the inductance of connecting leads will be greater than that of the resistor.

Voltage Coefficient

Maximum of – 5% / kV peak / cm, decreasing with resistivity.

Power Ratings

These are determined by the maximum permissible surface temperature of  220 °C. In free air, vertical mounting will provide better cooling than horizontal mounting. The load ratings in the table and the de-rating formula are for vertical mounting. Forced cooling will permit a considerable increase in loading.


Air, Oil, SF6.