24 Dec
2025
24 Dec
'25
4:09 a.m.
On Mon, Dec 22, 2025 at 01:42:54PM -0500, Paul Koning wrote:
I glanced at a few of them. Was surprised to see an
inverter using a 6L6. Then looked a little further and came across an element that uses
an 807.
The 6L6 and even more the 807 are rather substantial power tubes. 807s are commonly seen
in amateur radio transmitters in the 1940s and 1950s, good for 50 watts or so power
output. I have a couple, they are very nice tubes. I don't remember the 6L6 ratings;
20 watts, perhaps? Both are also rather large, the 807 especially, when compared to
typical "receiver" tubes.
Good catch. The majority of the 6L6s are used in parallel pairs in
the circuits identified as "transmitters." They are drivers for
transmission lines that can be up to about 80 feet long with taps
about every foot. The pulses they're transitting are about 2
micro-seconds long. So they really are like small RF transmitters
pushing long transmission lines pretty hard.
When I first saw those designs, I thought in terms of over-design
from the context of TTL signals on busses measured in inches. Then
again, we're talking about a 50 volt swing charging up a big long
coax capacitor. So the more I've dug into it, the more respect I
have for the design. In fact, there are also pulse amplifiers
that can be inserted to bump the signals on long lines.
One of these days, I'm hoping to write all this up into a thorough
technical description of the machine including all the modifications
that were made over its 10 year life. The scary part is that I've
been digging into it for about 10 years now.
BLS