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[vastonsmith]

Hello fellow forum members! It is a pleasure to share my first ever post in the Mic Lab with you all.

I would like to know if it is possible to safely re-tube a U67 microphone with an Amperex 6084, or other E80F type tubes that are 65.2mm in length, compared to the standard EF86 tubes that are 54.1mm.

I am concerned because although the longer E80F tube technically fits into a U67, the top of the tube is so close to the wires at the C12, C13, C14, and C1 solder points that I am afraid the heat generated by the tube may damage or partially melt the shielding of the wires

ahsan

[klaus]

When we issued the KHE mic, I tested several of the long-version E80F (these were Telefunken), and found them sonically deficient, compared to the sexy short-envelope E80F. So I would rather select by sound than by mechanical/thermal criteria.

No, the wires in your U67 will not melt from the modest heat generated by an impedance-conversion tube which burns little calories in the process (i.e. not much current, and therefore heat, generated in a U67).