Helping the EDSAC Project

There are several ways that you may be able to help.

  • Locate or donate components
  • Volunteer to help with the project
  • Support the project financially
  • Components

    If you have components which you think the project could use and wish to donate them, please email - but please check the lists below first to see if we need them. Dealers with stock to sell are also welcome to contact us.

    When you look at a photograph of EDSAC, the overwhelming impression is of rack after rack of thermionic valves (vacuum tubes) - about 3,000 of them! However, sourcing valves is not our main problem. Even though valves were superseded by solid-state electronic devices from the early 1960s, valve production continued for decades, as spares were needed for existing equipment. And indeed many valves are still produced today. Specialist dealers hold large stocks of the common types of valve, often over 60 years old and still unused!

    Our main problem is finding authentic ‘passive’ components such as resistors and capacitors and which are still 'in spec'. Manufacturers made much progress in the 1950s and later in miniaturising these, and if we were to use their modern equivalents, they would function perfectly but would ‘just look wrong’. In addition, while old resistors generally still work well, old capacitors often do not.

    Another problem is getting hold of the physical components which allowed the electronic components to be interconnected, such as terminal strips. We are having over 1,000 feet of terminal strips made by a specialist manufacturer to very close to the original specification. Valveholders are also hard to find; while many types are still manufactured they are most often not of the authentic dimensions..

    As of February 2014, we are still trying to source the following components:

  • Round, black moving coil meters, 3.25" outside diameter. Scaled 0-10, 0-20, 0-30 or 0-100, or up to 250-300V. They will be used as voltmeters, but milliamp meters will also be very useful. We need 15-20 in total.
  • About 30 large ~4k7 resistors (value not critical) with radial leads, resistor body approximately 1.75" long
  • 100 off WW2 vintage 4MFD 250V DC capacitors, Air Ministry stock number 10C/251, or close equivalent.
  • vintage resistors of a variety of values, tested and with a tolerance of 10% or better.
  • B9G valve-holders. Maximum diameter of raised part of socket 1.5 inches (38.1mm). Spacing of fixing hole centres 1.8125 inches (46.04mm). These dimensions are important as the metal chassis are being made to authentic dimensions. We have had to use some modern B9Gs of Chinese origin, but originals are much more authentic and suitable. We would still like to obtain up to 600-800 original B9Gs if possible.
  • Although we now have most if not all of the valves we need, donations of additional valves are very welcome as, once commissioned, we intend to keep the EDSAC replica running until at least 2040. The following are the main valve types used in EDSAC. Each type has several different designations. The number in brackets indicates approximately how many of each type EDSAC uses.

  • EF50, CV1091, VR91 (20)
  • EF54, CV1136, VR136 (1150)
  • EF55, CV173 (200)
  • EA50, CV1092, VR92 (600)
  • EB34, CV1054, VR54 (750)
  • CV1116, VR116 (30)
  • 12E1, CV345 (10)
  • CV685, VR150/30 (5)
  • ECR60, CV1097, VCR97 (10) (6" diameter cathode ray tubes)
  • CV1111 (4)
  • KT61 (10)
  • Volunteer

    During early 2014, we need volunteers with expertise in valve circuit design and nickel delay line construction. Through 2014 and 2015, we need people with skills in soldering, testing, assembling and wiring up racks.

    If you have these skills, and have sufficient spare time and enthusiasm to devote to the project, please email


    If you or your organization are interested in becoming a financial sponsor, please contact Andrew Herbert by emailing