30 Aug
2008
30 Aug
'08
7:42 a.m.
Chuck Guzis wrote:
My first exposure to very-low plate voltage
applications
was with a code-practice oscillator built from a circuit in the ARRL
Radio Amateur's Handbook. ISTR it used a 6SN7 that used the
6.3v from the heater winding as plate voltage. At any rate, it would
drive a pair of earphones. Perhaps someone with a RAH collection
from the 1950's might locate the circuit.
Thank you! That's the perfect tube multivibrator lead which allowed me to find these
references using "code oscillator" and "6SN7" as search terms:
p29, Dec '55: "A Heterodyne Crystal Calibrator AND CODE PRACTICE
OSCILLATOR" uses both halves of a 7N7, 6SN7, or 12AU7 (or pairs of many triodes) and
two crystals to give marker signals at the DIFFERENCE of the two crystals
p41, Jun '52: "...Frequency Standard...Oscillator" uses a 6F6
oscillator, both halves of a 6SN7 as a multivibrator
p30, Mar '62: Uses a 6AU6 oscillator at 100 kc and a 12AU7
multivibrator to also give 50 kc markers
p33, Jan '65: Uses a 6AQ5 oscillator at 100 kc and a 6AS6 10-kc
sub-harmonic generator (no diode and NO inductors!)
p34, May '65: Uses a 6AU6 oscillator at 100 kc, a 12AU7 multi-
vibrator for 10 kc points, and another 12AU7
All of these and more were found here:
http://newsgroups.derkeiler.com/Archive/Rec/rec.radio.amateur.homebrew/2007…
Do you recall if the p29, Dec '55 project was the 6.3V plate voltage project you
mentioned?
The successful use of 6.3V as the plate voltage in a multivibrator using a standard HV
tube is extremely encouraging. The lowest voltage used for the audio circuits I've
built was 24V which was most likely used to put the tubes in a more linear operating
region which wouldn't be necessary with a multivibrator.
While dual (identical) pentodes aren't too common
for
you to use the first grid as a space-charge element,
I wonder if one of the sync-separator tubes, such as the
6BU8 might not do the trick. Single cathode and first grid,
independent 3rd grids and plates.
Thanks, that will be an interesting thing to try.
In the 20's and 30's before small-geometry
power
tubes became available, "microwave" experimenters would take a
hefty triode and put a high positive voltage on the grid and a
slightly negative voltage on the plate to induce Barkhausen
oscillation. But that has nothing to do with your problem, so
forget that I mentioned
But thanks for mentioning it anyway since I'm interested in reading about any unusual
operating modes for tubes.
Bill
30 Aug
30 Aug
10:05 a.m.
On 30 Aug 2008 at 7:42, William Blair wrote:
Thank you! That's the perfect tube multivibrator
lead which allowed
me to find these references using "code oscillator" and "6SN7" as
search terms:
It all was very long ago. I can tell you what I see in my mind's eye
(however accurate that is). A small chassis with a filament
transformer on one side, an interstage audio transformer on the other
and an octal tube socket in the middle. A pot on the front to vary
the pitch and a phone jack. The tube was definitely a dual triode;
it might have been a 6SL7 or 6SN7 (perhaps in the application, it
didn't matter). Construction was from either the ARRL RAH or perhaps
"The Radio Handbook" from about the same time.
I'm almost 100% certain that this was no multivibrator application;
indeed, half of the triode may have been used as a rectifier.
All of this is subject to the bit-rot that increasingly pervades my
wetware nowadays.
Cheers,
Chuck
10:31 a.m.
On Saturday 30 August 2008 13:05, Chuck Guzis wrote:
On 30 Aug 2008 at 7:42, William Blair wrote:
Would that interstage transformer perhaps be making it a blocking oscillator?
I remember those (indeed using 6SN7s) being fairly common in very early TVs,
say 1950s or earlier.
Thank you! That's the perfect tube
multivibrator lead which allowed
me to find these references using "code oscillator" and "6SN7" as
search terms:
It all was very long ago. I can tell you what I see in my mind's eye
(however accurate that is). A small chassis with a filament
transformer on one side, an interstage audio transformer on the other
and an octal tube socket in the middle. A pot on the front to vary
the pitch and a phone jack. The tube was definitely a dual triode;
it might have been a 6SL7 or 6SN7 (perhaps in the application, it
didn't matter). Construction was from either the ARRL RAH or perhaps
"The Radio Handbook" from about the same time.
I'm almost 100% certain that this was no multivibrator application;
indeed, half of the triode may have been used as a rectifier. All of this is subject to the bit-rot that
increasingly pervades my
wetware nowadays.
I hate it when that happens!
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
31 Aug
31 Aug
10:19 a.m.
Back to the 1951 ARRL, the device was called a 'monitone' and used
a 6SL7 with a phone jack on the one grid and the output of a
6J5 on the other grid after biasing and volume control and an
osscillator that used a neon bulb a capacator and biasing
resisters. Transmitter input was to 6J5 and effectively to side one of
6SL7 through another resister. If I could draw in ascii I'd
show this device.
bs
On Sat, 30 Aug 2008, Chuck Guzis wrote:
On 30 Aug 2008 at 7:42, William Blair wrote:
Thank you! That's the perfect tube
multivibrator lead which allowed
me to find these references using "code oscillator" and "6SN7" as
search terms:
It all was very long ago. I can tell you what I see in my mind's eye
(however accurate that is). A small chassis with a filament
transformer on one side, an interstage audio transformer on the other
and an octal tube socket in the middle. A pot on the front to vary
the pitch and a phone jack. The tube was definitely a dual triode;
it might have been a 6SL7 or 6SN7 (perhaps in the application, it
didn't matter). Construction was from either the ARRL RAH or perhaps
"The Radio Handbook" from about the same time.
I'm almost 100% certain that this was no multivibrator application;
indeed, half of the triode may have been used as a rectifier.
All of this is subject to the bit-rot that increasingly pervades my
wetware nowadays.
Cheers,
Chuck
10:42 a.m.
On 31 Aug 2008 at 13:19, schwepes at moog.netaxs.com wrote:
Back to the 1951 ARRL, the device was called a
'monitone' and used
a 6SL7 with a phone jack on the one grid and the output of a
6J5 on the other grid after biasing and volume control and an
osscillator that used a neon bulb a capacator and biasing
resisters. Transmitter input was to 6J5 and effectively to side one of
6SL7 through another resister. If I could draw in ascii I'd
show this device.
Nope, not it. It was definitely a CPO and not a monitor. Single
tube, no neon bulb, line powered via a single 6.3v filament
transformer. As I said, it may not have been from the RAH. But I
built and used it. I suppose I could reconstruct it with parts from
my hellbox if anyone was really curious (I think I still have an
interstage audio transformer kicking around). I think Roy nailed it
though when he suggested a blocking oscillator--one doesn't require
much gain to work.
Cheers,
Chuck
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