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.
Are you disappointed that there are no longer any good 811A tubes available? If so, read more! I’ve discovered that NOS tubes are still available from the factory that made the Svetlana 811A that was quite popular with hams and enjoyed a good reputation. As a bonus, they’re cheaper than current production Chinese 811A tubes!
The tubes are the Ryazan G-811, here is the datasheet: Ryazan G-811
The tube in the picture on the Ryazan website is actually the Svetlana 811A product, which is now no longer manufactured. The NOS Ryazan tubes have a black base and no plate cap insulator (which was never needed), but are otherwise identical. Read more for the full story!
Last night I got an email from John Isabella, K1IF, stating that he’d read my blog regarding my Diamond X510, and was wondering if I knew what voltage the capacitors inside were rated at.
I confessed that I didn’t, as mine did not seem to be in need of replacing, but with a bit of math we were able to ascertain some suitable ratings, namely 300V rated 2pf capacitors. If you’re interested in the math, continue reading.
There is now a part 2 to this article which covers replacing the capacitors found in the antenna, if you’re more interested in that aspect of repair, please have a look here. Otherwise, read on for my solution to a broken Radome.
Background, Specifications & Waffle
At the start of my adventures into Amateur radio, I was lucky enough to be given all kinds of gear by the very friendly VK3HBN as an incentive to getting licensed – after all, who can sit by idly looking at lots of toys that they can’t play with?
One of these items was a lovely (read expensive) Diamond X510MA Dual Band Base Station Vertical Antenna. The specifications are as follows:
- 8.3 dB Gain on 2M (3x 5/8 Elements, Centre Loaded Co-Linear)
- 11.7 dB Gain on 70CM (5x 5/8 Elements, Centre Loaded Co-Linear)
- Max Power 200W FM (and more than likely SSB, remembering that phasing capacitors have Vpeak limits)
- 5.2 Metres tall with 3x 52cm Radials at feed point
- 3 Piece construction
There was however, but one catch
The antenna had suffered a slight mishap. Although details are scarce – perhaps to protect the reputations of third parties – the bottom section of the antenna had suffered a clean break as the consequence of a fall. While the antenna had previously been repaired by placing a section of 32mm PVC pipe over the break combined with some PVC Adhesive and ‘gaffer’ tape for sealing purposes, the repair had come loose and was looking somewhat worse for wear – I decided it was time for a complete overhaul. Details Below.