This particular tube tests very strong, although it’s not the most balanced tube. Often square-getter Mullards are associated with mC1 production codes, and the halo-getter tubes with f91 and later codes. Oddly though, this particular tube has an f91 code AND a square-getter. The f91 code on this tube is Extremely faint, and is almost impossible to see with a naked eye even under good light (and even more difficult to photograph, but I think I managed to barely capture it with a back-light enough to sort-of see it’s faint outline). The print on the tube is very fragile and will easily rub off, some has already rubbed off, special care was taken not to rub off any more while testing. The tube’s test results are displayed in the photos (New 12AX7 Spec 100% = 1,600 Gm). See the photos for physical / cosmetic condition. Part of the design is a little springy shock absorber the keeps the tube safely centered in the box and from rattling around. Notes Regarding Tube Tests. All tubes are tested on an Amplitrex AT-1000 tester in the automatic Fixed Bias Mode (for the most conservative results). Test Results are for a general reference only, and are not a guarantee of performance, nor a guarantee of how they will test on your tester. No real world (audio) performance measurements are taken.

Great amp in great shape! Includes upgraded long plate Sylvania vintage tube, which really enhances the tone.

This particular set tests strong and are closely balanced / matched. The print on these tubes is fragile and will easily rub off, some has already rubbed off, special care was taken not to rub off any more while testing. The tubes’ test results are displayed in the photos (New 12AX7 Spec 100% = 1,600 Gm). See the photos for physical / cosmetic condition. Notes Regarding Tube Tests. All tubes are tested on an Amplitrex AT-1000 tester in the automatic Fixed Bias Mode (for the most conservative results). Test Results are for a general reference only, and are not a guarantee of performance, nor a guarantee of how they will test on your tester. No real world (audio) performance measurements are taken.