R J Carpenter wrote:

"Rob Judd" wrote in message
...

Open-air triode?? Do tell, you have me fascinated...

IIRC, field effect triodes {FETs} were made about the same time as the first
vacuum tubes, but they didn't work well enough, given materials technology
of the day.

I thought that FETs dated to the early 30s. De Forest's "audion" was
invented in 1903 and made long-distance telephony practical by 1913.

Jerry

P.S. to Rick: That was before my time.
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

R J Carpenter wrote:

"Rob Judd" wrote in message
...

Open-air triode?? Do tell, you have me fascinated...

IIRC, field effect triodes {FETs} were made about the same time as the first
vacuum tubes, but they didn't work well enough, given materials technology
of the day.

I thought that FETs dated to the early 30s. De Forest's "audion" was
invented in 1903 and made long-distance telephony practical by 1913.

Jerry

P.S. to Rick: That was before my time.
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Jerry Avins wrote:

Rob Judd wrote:

...

Open-air triode?? Do tell, you have me fascinated...

Rob

I wrote of it before, so I'll be brief and hope I'm not boring. An
open-coil hot plate with a ceramic holder to support and contain the
nichrome element as filament*. Topped with galvanized window screening,
the zinc removed with muriatic acid so as not to noxiously sublime,
resting on the ceramic as (literally!) grid. Small glass beads -- around
1/16" -- scattered on it to create a gap and hold the screening flat.
Atop that, a pie tin weighted with cooling water to serve as
(literally!) plate. With 700 volts on the plate, I got measurable
current on my 1000 ohm/volt meter. At -90 volts on the grid, the current
was too small to read. The gain was enough to sustain oscillation.

Très bizarre!

Rob

Jerry Avins wrote:

Rob Judd wrote:

...

Open-air triode?? Do tell, you have me fascinated...

Rob

I wrote of it before, so I'll be brief and hope I'm not boring. An
open-coil hot plate with a ceramic holder to support and contain the
nichrome element as filament*. Topped with galvanized window screening,
the zinc removed with muriatic acid so as not to noxiously sublime,
resting on the ceramic as (literally!) grid. Small glass beads -- around
1/16" -- scattered on it to create a gap and hold the screening flat.
Atop that, a pie tin weighted with cooling water to serve as
(literally!) plate. With 700 volts on the plate, I got measurable
current on my 1000 ohm/volt meter. At -90 volts on the grid, the current
was too small to read. The gain was enough to sustain oscillation.

Très bizarre!

Rob

That bulb was probably an old coiled 'Edison' type . They were /are
known to
form a tuned circuit resonating in the old TV band 1 ( about 48 - 62
MHz)
acting as a TX when power is applied.

Frank GM0CSZ / KN6WH

Thank you thankyouthankyou! I've been called a crazy liar more than once
over that bulb. There was no channel 1 when that incident happened, but
I suppose that a small change of geometry could raise the frequency. The
explanation in QST had it that the frequency was swept over a fairly
large range as the voltage varied during a cycle.

I found such a bulb in the loft of the garage of a house we were
renting in the mid-1950s. I had read an article about them somewhere,
so I took it inside, screwed it into a lamp near the TV, and, voila,
instant Channel 3 TVI (that was the main channel in Milwaukee,
WI, then). I put it in a box in my shack, and didn't think about it for
some time.

I put up a tower and 20 meter beam. Before the coax was in the house,
a neighbor sent his kid over to complain about TVI. I invited him to
come over and see that the TV in my shack was not showing any
interference, but he declined, and continued to complain over the next
few months.

While preparing to leave for two weeks vacation, I had a flash of
inspiration. I put the bulb in a lamp, connected a timer to the lamp,
and put it in a closet (so the light couldn't be seen in an otherwise
dark house). The timer turned the bulb on during evening TV
hours.

I left it on for several days after our return. The neighbor never
complained of TVI again.

73, John - K6QQ, glad for the statute of limitations.

That bulb was probably an old coiled 'Edison' type . They were /are
known to
form a tuned circuit resonating in the old TV band 1 ( about 48 - 62
MHz)
acting as a TX when power is applied.

Frank GM0CSZ / KN6WH

Thank you thankyouthankyou! I've been called a crazy liar more than once
over that bulb. There was no channel 1 when that incident happened, but
I suppose that a small change of geometry could raise the frequency. The
explanation in QST had it that the frequency was swept over a fairly
large range as the voltage varied during a cycle.

I found such a bulb in the loft of the garage of a house we were
renting in the mid-1950s. I had read an article about them somewhere,
so I took it inside, screwed it into a lamp near the TV, and, voila,
instant Channel 3 TVI (that was the main channel in Milwaukee,
WI, then). I put it in a box in my shack, and didn't think about it for
some time.

I put up a tower and 20 meter beam. Before the coax was in the house,
a neighbor sent his kid over to complain about TVI. I invited him to
come over and see that the TV in my shack was not showing any
interference, but he declined, and continued to complain over the next
few months.

While preparing to leave for two weeks vacation, I had a flash of
inspiration. I put the bulb in a lamp, connected a timer to the lamp,
and put it in a closet (so the light couldn't be seen in an otherwise
dark house). The timer turned the bulb on during evening TV
hours.

I left it on for several days after our return. The neighbor never
complained of TVI again.

73, John - K6QQ, glad for the statute of limitations.