For some reason, I seem to have become a little obsessed with 811A tubes whilst playing around with an Ameritron AL-811 Amplifier.
One of the best sources of information on the matter is Tom (W8JI)’s site; he has a great page here: 811A tube 572B tube history.
Although its fantastic, Tom’s page doesn’t really help you evaluate the current market for 811A tubes; you’ll learn a lot about them, but not about which tubes are better than others.
So far, I have identified 3 options on the market at the moment:
- Ryazan G-811 (NOS, made in the former USSR): ~$18 USD / tube
- Shuguang FU-811 (Current production, often rebranded, Chinese): >$25 USD / tube
- RCA 811A (NOS, USA Made): >$45 USD / tube
The Shuguang tube is the most commonly used 811A variant, mainly due to the fact that they are reasonably cheap and manufacturers can buy decent stock quantities constantly. That said, they are by far the worst quality of the lot, often made to very poor standards – I had 3/4 in a recent batch develop cracks in the anode along folds, where the sheet metal press had left scratches. The only real benefits to Shuguangs are that they are currently being manufactured, and if you live near a dealer (I don’t) you can get them replaced under warranty.
The RCA tubes are by far the best made and best designed. As Tom states on his website, they have slightly higher power handling (anode dissipation), and better transient overload (mistuning, or peak power) handling. The downside is they are very expensive, and often suffer from the glued parts coming lose. Whilst the base of the tube often comes loose, the biggest issue with RCA (Electronic Enterprises & Cetron) tubes is if the anode plate cap becomes detached and cracks the envelope. Always be very very careful when working with expensive RCA tubes. They can also get a little ‘gassy’, so it is advisable to hi-pot test them before use. Unfortunately, these attributes make them less suitable for people who just want to ‘plug and play’.
The Ryazan G-811 is an interesting tube. It has the same design as the Shuguangs (I suspect the tooling was shared amongst communist countries), except that it doesn’t use a flash getter during manufacturing. As such, it is completely clear with no silver spots. This suggests to me they were able to achieve a very ‘hard’ vacuum when manufacturing, which is probably why they seem to have held up well in storage. I personally think these tubes are a bargain; whilst they’re not quite as good as RCAs, they are the cheapest of the lot, and are definitely made to higher standards than the Shuguangs. Whilst none of the tubes come close to the RCA quality, the Ryazans are great quality where it counts; I only mark them down due to cosmetics. It is worth noting that Ryazan was the manufacturer who produced Svetlana’s 811A product.
Well thats about all I know about 811As 😉 I’ve got sets of all 3, and whilst the RCAs are nice, the Ryazans are by far the best value!