AVVT Overhauled tubes
We do this at EML factory. We are probably the only company able to do this.
We have the possibility to overhaul any defective AVVT solid plate tubes, but prices of this is higher than buying new Emission Labs tubes. Reason is, when building new tubes, we can take unused, cleaned parts from stock. When overhaul an AVVT tube, we have to take the old tube fully apart which is time consuming. Then, the old parts must be re-shaped and repaired, then cleaned with by sand blasting, then chemical cleaning, and then vacuum heating. So this is all a lot of work, but the result is the AVVT tube with most of it's original parts, and in far better quality as ever made by AVVT.
Optics: Will be the almost the same, see below for differences:
Heaters: we use the darker glowing Emission Labs heaters, which have a multiple life time as the AVVT heaters.
Tube data: The AVVT grids can not not be re-used. We use new grids, belonging to the EML heaters. Result of this is, the tubes come out with somewhat lower Transconductance (Gm) as AVVT made them, but within tolerance. As long as you understand, the lower Gm is by construction, and not because of lower emission, all is ok. The difference is small.
Tube hum: Will be significantly lower as with AVVT, due to better quality control.
Glass shape: For 32B we use similar glass shape as AVVT. The 300B is overhauled, using the same glass shape as EML 300B.
Lifetime: Lifetime of these tubes will be a higher as when made by AVVT.
Guarantee: Three months on all manufacturing failures.
Mechanical strength: We replace the (very soft) side bars of AVVT by a hard metal, same as we use this at EML. So risk on postal damages becomes low.
When you have a pair of defective AVVT tubes, you can send them in, and you receive the overhauled pair, ready from stock. The tubes you send in, should not have broken glass.