29 Aug
2008
29 Aug
'08
12:13 p.m.
Chuck Guzis wrote:
Just before transistors began to be used in auto
radios, "space
charge" tubes made a brief appearance, running their plates and
heaters from the 12v battery. No vibrator supply. Some of the
earliest transistor designs used a transistor only in the audio
output stage, among them the Delco "Wonder Bar" models.
Jeff Duntemann has a nice page on this stuff, along
with datasheets:
Yes, I found that excellent site back when I was playing with low-voltage tube headphone
amps and I have a copy of the Tube Collector Magazine "Car Tubes" article cited
there. However, the tube amps I built from modern plans were ones that used common dual
triodes like the 12AU7 but with _very_ low plate voltages. The reason for this is the
scarcity and, as a result, expense of the low-voltage "car tube" types most
useful for audio amps and, unfortunately, logic circuits (12U7, 6GM8). If for some reason
I can't get any of the most common and cheapest high B+ dual triode tubes to work in a
logic circuit at low plate voltages, then I'll have to go with something like the dual
diode, single triode "space charge" car tubes that aren't in demand by audio
enthusiasts making them much more readily available and much cheaper. A functional
hobbyist demonstration of tube logic that's cheap and uses low voltages is my goal.
29 Aug
29 Aug
1:13 p.m.
On 29 Aug 2008 at 9:13, William Blair wrote:
Yes, I found that excellent site back when I was
playing with
low-voltage tube headphone amps and I have a copy of the Tube
Collector Magazine "Car Tubes" article cited there. However, the tube
amps I built from modern plans were ones that used common dual triodes
like the 12AU7 but with _very_ low plate voltages.
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.
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.
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 it.
Cheers,
Chuck
2:46 p.m.
Yes, I found that excellent site back when I was
playing with low-voltage tube headphone amps and I have a copy of the Tube Collector
Magazine "Car Tubes" article cited there. However, the tube amps I built from
modern plans were ones that used common dual triodes like the 12AU7 but with _very_ low
plate voltages. The reason for this is the scarcity and, as a result, expense of the
low-voltage "car tube" types most useful for audio amps and, unfortunately,
logic circuits (12U7, 6GM8). If for some reason I can't get any of the most common
and cheapest high B+ dual triode tubes to work in a logic circuit at low plate voltages,
then I'll have to go with something like the dual diode, single triode "space
charge" car tubes that aren't in demand by audio enthusiasts making them much
more readily available and much cheaper. A functional hobbyist demonstration of tube
logic that's cheap and uses low voltages is my goal.
I have exactly one 12U7 in stock. I have a few 12K5s, as well.
One thought about using space charge tubes for logic - they might end
up being slow as molasses.
--
Will
4:30 p.m.
William Blair wrote:
If for some reason I can't get any of the most
common and cheapest
high B+ dual triode tubes to work in a logic circuit at low plate
voltages, then I'll have to go with something like the dual diode,
single triode "space charge" car tubes that aren't in demand by audio
enthusiasts making them much more readily available and much cheaper.
A functional hobbyist demonstration of tube logic that's cheap and
uses low voltages is my goal.
I've updated my web page about the ASM with some commentary about the gate
design, if interested (http://www.cs.ubc.ca/~hilpert/e/ABC/asm.html). Following
from what is written there, if one is setting out to
create a tube logic gate
design with resistive inputs I would lean towards a
positive-logic-NAND /
negative-logic-NOR approach where there is only one condition (input state)
driving the tube to saturation. Resistor values would still have to change
depending on the number of gate inputs.
Neon bulbs for each input were one of the other techniques used to avoid the R
problems (no help for a low plate voltage design obviously). "DVL" logic might
be interesting at low plate voltage.
5878
days inactive
5878
days old
3 comments
4 participants
participants (4)
-
cclist＠sydex.com -
hilpert＠cs.ubc.ca -
wbblair3＠yahoo.com -
wdonzelli＠gmail.com