These tubes are beginning to really wake up at 500v 50 mA. This is a reasonable dissipation for 300Bs, and it is just tickling the Vaic and Svetlana tubes. Note that they were quite close together, except for the Cetron which was very poor throughout. In such tests, due to the small samples (only a single tube in the case of the Shuguang), a difference of 0.05% is not really significant. Since the Vaic and Svetlana types can be run harder than 300Bs, (and they definitely sound better when this is done), they should be run harder in order to take advantage of their greater dissipation capacity. The 50s were not tested at 500v as they are rated for 450v maximum. The 500v 75 mA test was at the outer limits for conventional 300Bs. In fact, the fellow who loaned the WEs for the test would NOT allow them to be run that hard. He worried that they might be destroyed, and he might be correct. And since these things are selling USED for $200-$300 each on the street, we decided to let it lie. But the Shuguang 300B was able to tolerate the power for a quick test (this was at the verge of redness on the plate). The SV811s and VV30Bs cheerfully absorbed it and begged for more. In fact, I ran 120 mA into an SV811-10 and a VV30B at 500v; no problem, no color was observed on the plates, and distortion was around 0.10% for both. We were unable to test the Cetrons at 75 mA.

Note that the load impedance used for testing all of these tubes was 3200 ohms. This was conservative for the 300Bs, but rather low for the SV811s. Even so, the SV811s gave distortion figures on a par with the best 300Bs, indicating that SV811s are more load-tolerant than most receiving power triodes.

Final conclusions:
1. The VV30B is an excellent tube, recommended for either 300B retrofit or for higher-power operation.
2. The SV811 is also excellent, though it is not compatible with existing amplifiers. It should be a serious contender for OEM and hobbyist use.
3. The Shuguang 300B is surprisingly good quality, but it obviously has limits on dissipation. It seems to use materials similar to other Shuguang tubes, so lifetime is expected to be less than that of the other brands.
4. Richardson has got problems: the first Cetron 300B we got developed a filament-to-grid short upon plugging into the amp. Even with 4.0vDC on the filament, it still shorted out. THIS IS SERIOUS TROUBLE. The second sample worked, but its filament was splayed out rather than staying in a flat plane; thus, performance was the worst of the lot, as was the sound. Its materials appear good, but quality control is very poor. Two good-used 1994 samples we borrowed worked OK, so maybe a bad 1995 lot was involved.

We are presently negotiating with Westrex for samples of the new production WE 300B; delivery date unknown. And the same is being done with New Sensor for samples of the recently-announced Sovtek 300B.