(Avery Fineman) wrote in message ...
In article ,
(Bruce Kizerian) writes:

I have seen remote cutoff pentodes such as the 1T4 used in
regenerative receivers. I'm guessing there is a good reason...perhaps
something to do with the decrease in gain with increasing signal
level...so that the pentode oscillator "fights" going into to
oscillation enough to give a very smooth transistion...rather than the
more abrupt transistion of some solid state circuits.

A 1T4 is an old directly-heated cathode tube. Played with those
a 56 years ago...in regenerative receivers...:-)

Looking back at those old magazine article projects, I'd surmise
that the "reason" a particular tube was used was that it was
AVAILABLE to use.

A regen operates at the hairy transition of self-oscillation where
positive feedback yields a tremendous increase in gain. Doesn't
matter whether it is vacuum tube or transistor. The only difference
between remote-cutoff and sharp cutoff characteristics (transistors
of the bipolar junction type are very sharp cutoff equivalents to
tubes) would be on the amount of spurious garbage created when
the regen jumps into full oscillation.

I know of no solid state equivalent (without some sort of AGC feedback
loop) for the remote cutoff pentode. Does anyone know if there is?

"AGC in a regen?" If you bias the control grid of a 1T4 about all you
will do is change the feedback setting for that hairy transition just
prior to going into self-oscillation.

And speaking of the 1T4...has anyone played with these enough to give
me some ideas for using them in regenerative radios.

The last time I played with battery-filament tubes (including the 1T4)
was in helping a friend restore an AN/PRC-8 Korean War era walkie-
talkie in the 70s (I wore one once in 1953). Nice VHF FM transceiver
very stable. The first time I played with a 1T4 was in a regenerative
receiver back in 1947 and it was very touchy on feedback setting
versus frequency on MF to HF bands (plug-in coil thing).

I also wondering
how much you can starve the plate and still get good results in a
regen receiver.

Experiment with it. There's not a large amount of data on regenerative
receivers any more and very little in the way of vacuum tube info.
A 1T4 power demand is minimal, 1.5 VDC filament at 50 mA and about
2.4 mA plate and screen current at 45 VDC supply. [183 mW total
supply drain] That's fairly "starved" considering the transconductance
is only 700 umhos (typ) at 0 VDC control grid. Even at "maximums"
of 90 V plate and 67 V on screen, the transconductance is only 900
umho.

There is loads of info on the net about regenerative recievers and
there are quite a few tube manuals online and lots of tube
information.

Most of the homebrews I have seen using the 1T4 use it hooked up in a
triode confiquration.........

Search the net.......Tube mansual online, tube data online,
regenerative recievers, homebrew tube radios,.......all the info you
want and more is on the net.

A 1L4 is a close cousin to the 1T4 as a sharp-cutoff pentode, same
envelope, filament, etc., but the gm is about ten percent higher. A
3Q4 or 3S4 (a 1S4 was made but was not recommended for new
designs back in 1956) has a gm of 1500 umho at twice the filament
voltage and 8.8 mA plate+screen at 90/67 V. Those "power pentodes"
have a semi-remote-cutoff characteristic. [800 mW power supply
demand would be "power" from a battery pack way back then...]

Regenerative receivers were all the rage among hobbyists back
about 1930 when tubes were relatively expensive and lacked
transconductance for effective RF amplification. Such were a
cheap way to get more sensitivity out of a single tube stage...but at
the expensive of instability and lack of uniform selectivity. Once the
superheterodyne was into production, it proved far better overall.

For experimentation purposes, a high gain-bandwidth product op-amp
IC might produce some interesting results. The gain-bandwidth (or
0 db open-loop gain frequency) of some op-amp ICs is up at 30 to
70 MHz now and the DC open-loop gain is enormous in comparison
to vacuum tubes. I sense possibilities of an op-am regen or even a
superregen on up through HF. Just a thought... :-)

Len Anderson
retired (from regular hours) electronic engineer person

I have used the 1Q5 with 18 volts and it worked well. It worked better with
27 volts.

Bill, N5NOB

I have used the 1Q5 with 18 volts and it worked well. It worked better with
27 volts.

Bill, N5NOB

Bruce Kizerian wrote:

But it does matter. In the heirarchy of regen devices tubes provide
the "smoothest" regeneration, followed by FETs, with bipolar
transistors generally taking a distant third. I am not asking because
I have never built a regen. I have built DOZENS of them, and I sell a
simple version on my website...but I'm always looking for a new
approach.

My first regen RX was in 1947 with an A415 direct filament triode. (Does
anyone remember it?) It was followed by DC11 - a steel 1.5 V filament
tube - both excellent ones for regen receivers. (We used to call them
Audions.) Bruce says there are three types of regens : with tubes, with
FETs and with bipolar transistors. There is also a forth type: a
negative resistance reganeration receiver, an invention of mine (also
known as Lambda receiver). You can find its scematic in the British QRP
Club's magazine SPRAT: number 111, page 4 - with a correction in number
112, page 25, and a complete construction in SPRAT 113, page 17 - with a
correction in SPRAT 114, page 24. The schematic is a simulation of a
tunnel diode and works in the negative part of the U/I characteristic.
It does not have a feedback coil, and the regeneration is very soft - so
the worst problem has been solved. Its stability is not convenient for
CW or SSB, but it is excellent for broadcast stations from 500 kHz to 30
MHz; a real project for beginners. If someone duplicates it, I will be
happy to hear about his experience - by e-mail
. hr) or on this group. Best wishes,
Bozidar, 9A2HL

Bruce Kizerian wrote:

But it does matter. In the heirarchy of regen devices tubes provide
the "smoothest" regeneration, followed by FETs, with bipolar
transistors generally taking a distant third. I am not asking because
I have never built a regen. I have built DOZENS of them, and I sell a
simple version on my website...but I'm always looking for a new
approach.

My first regen RX was in 1947 with an A415 direct filament triode. (Does
anyone remember it?) It was followed by DC11 - a steel 1.5 V filament
tube - both excellent ones for regen receivers. (We used to call them
Audions.) Bruce says there are three types of regens : with tubes, with
FETs and with bipolar transistors. There is also a forth type: a
negative resistance reganeration receiver, an invention of mine (also
known as Lambda receiver). You can find its scematic in the British QRP
Club's magazine SPRAT: number 111, page 4 - with a correction in number
112, page 25, and a complete construction in SPRAT 113, page 17 - with a
correction in SPRAT 114, page 24. The schematic is a simulation of a
tunnel diode and works in the negative part of the U/I characteristic.
It does not have a feedback coil, and the regeneration is very soft - so
the worst problem has been solved. Its stability is not convenient for
CW or SSB, but it is excellent for broadcast stations from 500 kHz to 30
MHz; a real project for beginners. If someone duplicates it, I will be
happy to hear about his experience - by e-mail
. hr) or on this group. Best wishes,
Bozidar, 9A2HL

Bruce Kizerian wrote:

But it does matter. In the heirarchy of regen devices tubes provide
the "smoothest" regeneration, followed by FETs, with bipolar
transistors generally taking a distant third. I am not asking because
I have never built a regen. I have built DOZENS of them, and I sell a
simple version on my website...but I'm always looking for a new
approach.

I built my first regenerative receiver in 1947 with an A415
direct filament tube, followed by one with a steel DC11 - 1,5 V
direct filament tube - both excellent ones for the purpose. (Does
anyone remember them?). Bruce says there are three types of regen
receivers: the tube ones, the ones with a FET, and the ones with bipolar
transistors. However, there is also a fourth one: the negative
resistance reganerative receiver, known also as a Lambda receiver . The
oscillator is a transistor immitation of the tunnel diode, and the
negative resistance substitutes the feedback coil. It is my own
construction. You can find its schematic in the British QRP Club
magazine SPRAT No. 111, page 4 (with a correction in No. 112, page 25).
The whole construction with a PCB has been published in SPRAT No. 113,
page 17 (with a correction in SPRAT 114, page 24). The RX does not have
a feedback coil, and the regeneration is very smooth and rather even
over the whole band. So, that problem has been solved for good. It is
not stable enough for CW or SSB, but it is excellent for AM
broadcast stations from 500 kHz up to 30 MHz (with corresponding coils,
of course). So, according to my opinion, it is excellent for beginners
because they do not have to bother with the feedback coils.

If anyone would care to duplicate it, I would appreciate it
very much if I could hear about his experiences with it (on this group
or by e-mail: ). The whole project is still
open for experimentation. Best wishes,

Bozidar, 9A2HL

Bruce Kizerian wrote:

But it does matter. In the heirarchy of regen devices tubes provide
the "smoothest" regeneration, followed by FETs, with bipolar
transistors generally taking a distant third. I am not asking because
I have never built a regen. I have built DOZENS of them, and I sell a
simple version on my website...but I'm always looking for a new
approach.

I built my first regenerative receiver in 1947 with an A415
direct filament tube, followed by one with a steel DC11 - 1,5 V
direct filament tube - both excellent ones for the purpose. (Does
anyone remember them?). Bruce says there are three types of regen
receivers: the tube ones, the ones with a FET, and the ones with bipolar
transistors. However, there is also a fourth one: the negative
resistance reganerative receiver, known also as a Lambda receiver . The
oscillator is a transistor immitation of the tunnel diode, and the
negative resistance substitutes the feedback coil. It is my own
construction. You can find its schematic in the British QRP Club
magazine SPRAT No. 111, page 4 (with a correction in No. 112, page 25).
The whole construction with a PCB has been published in SPRAT No. 113,
page 17 (with a correction in SPRAT 114, page 24). The RX does not have
a feedback coil, and the regeneration is very smooth and rather even
over the whole band. So, that problem has been solved for good. It is
not stable enough for CW or SSB, but it is excellent for AM
broadcast stations from 500 kHz up to 30 MHz (with corresponding coils,
of course). So, according to my opinion, it is excellent for beginners
because they do not have to bother with the feedback coils.

If anyone would care to duplicate it, I would appreciate it
very much if I could hear about his experiences with it (on this group
or by e-mail: ). The whole project is still
open for experimentation. Best wishes,

Bozidar, 9A2HL

Thanks everyone for the interesting and useful information.

For the record, I am not particularly in love with tubes, but if there
is something they will do better than solid state devices I'm willing
to give it a try. When I can buy PN2222 bipolars for $.02ea and PN4416
JFETS two for a quarter, and dual gate MOSFETS for a nickel, the
expenditure for one of those fragile glass things better be well worth
it. It can' be different or just a little better. It has to be "knock
your socks off" superior...I make radio kits for kids and schools and
I want them to be able to afford the purchase.

Bruce kk7zz
www.elmerdude.com

Thanks everyone for the interesting and useful information.

For the record, I am not particularly in love with tubes, but if there
is something they will do better than solid state devices I'm willing
to give it a try. When I can buy PN2222 bipolars for $.02ea and PN4416
JFETS two for a quarter, and dual gate MOSFETS for a nickel, the
expenditure for one of those fragile glass things better be well worth
it. It can' be different or just a little better. It has to be "knock
your socks off" superior...I make radio kits for kids and schools and
I want them to be able to afford the purchase.

Bruce kk7zz
www.elmerdude.com

People here have recently mentioned tubes intended for portable
operation, with plate voltages of around 20 volts. Much more common are
tubes intended for running from mains-powered supplies. These mostly
require plate voltages that can be lethal. You should consider this when
designing kits for kids.

Roy Lewallen, W7EL

Bruce Kizerian wrote:
Thanks everyone for the interesting and useful information.

For the record, I am not particularly in love with tubes, but if there
is something they will do better than solid state devices I'm willing
to give it a try. When I can buy PN2222 bipolars for $.02ea and PN4416
JFETS two for a quarter, and dual gate MOSFETS for a nickel, the
expenditure for one of those fragile glass things better be well worth
it. It can' be different or just a little better. It has to be "knock
your socks off" superior...I make radio kits for kids and schools and
I want them to be able to afford the purchase.

Bruce kk7zz
www.elmerdude.com