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Tube Matching 101

Tube Matching 101

There is a lot of confusion about matching tubes. It starts with some vendors, especially on eBay, matching tubes by the way they look (visual matching) to matching on multiple electrical parameters at the same time.

There are 4 parameters that could be used to match preamp tubes:

  1. Transconductance – Gm
  2. Voltage Gain – Mu
  3. Plate Current – Ip
  4. Tube Age
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CBS-Hytron 5814A – Engineering Samples

CBS-Hytron 5814A - Engineering Samples

Once in a while, while going through a new shipment of tubes, I find some true treasures. This time it was an incredible find, the legendary CBS-Hytron 5814 tubes, but not just that, they were engineering samples from CBS-Hytron. Engineering samples were sent to various manufacturers to get acceptance and determine interest before starting mass production. Unfortunately, there is no date code on the box or the tubes, so it’s hard to say when it was produced exactly, but considering that 5814 tubes have been produced since October 1949, these are not far behind. Notice, that there is not 5814 label on the glass, just on the wrapper.

I’ve already written about these tubes and there are also posts about comparing them to other tubes from other contributors.