[pmmunro]

The glass tube form of resistor was the subject of two Patents assigned to Harold Edward Bayliss both applied for on March the 9th 1942 and accepted on the 17th December 1943. This would set the date at which these components could have been intriduced commercially.

The first patent concerns embedding the resistance medium in a coating on the tube as the resistor is wound to improve the mechanical stability of the wire. The second concerns the use of pressed out tabs in the clamp bands to provide an attachment point for the winding.

H E Bayliss took out these patents in his own name but later also had joint patents for winding machine accessories with ACWEECO, so may have been an employee of the company, at least at some period. He seems to have been a specialist in detail improvements in resistor manufacture.

In my experience, it is very rare to find a glass tube resistor of this type which is not open circuit, possibly due to stresses on the extremely fine wire used. In the long term, I do not think this type of resistor could be considered a success.

Concerning Andy's comments about the construction of the Type 'D' Avometer, I think it would be fair to think of those produced during the middle war years as having "Utility" construction due to shortages of specialist materials, such as the contact material for the cut-out. I don't think this is true of the corresponding Admiralty Pattern 47A & 48A; perhaps the Admiralty was less willing to take a pragmatic view than the Air Ministry.

PMM