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.

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?

And speaking of the 1T4...has anyone played with these enough to give
me some ideas for using them in regenerative radios. I also wondering
how much you can starve the plate and still get good results in a
regen receiver.

Thanks

Bruce Kizerian
www.elmerdude.com

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.

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

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.

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

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.

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 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?"

Here, I was speaking in more general terms and not referring to
regenerative circuits.



Experiment with it.

I plan on it.


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... :-)

The voltage gain of an effective regenerative stage is can be as high
as 100,000 as reported by Charles Kitchin. That's 100dB...not many op
amps have that kind of gain at say 10MHz.

Thanks for your comments. I always appreciate hearing from folks with
lots of valuable radio experience to share.

Bruce kk7zz
www.elmerdude.com

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.

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 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?"

Here, I was speaking in more general terms and not referring to
regenerative circuits.



Experiment with it.

I plan on it.


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... :-)

The voltage gain of an effective regenerative stage is can be as high
as 100,000 as reported by Charles Kitchin. That's 100dB...not many op
amps have that kind of gain at say 10MHz.

Thanks for your comments. I always appreciate hearing from folks with
lots of valuable radio experience to share.

Bruce kk7zz
www.elmerdude.com

In article ,
(Bruce Kizerian) writes:

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.

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 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?"

Here, I was speaking in more general terms and not referring to
regenerative circuits.

If you are speaking in general terms then there are plenty of gain-
control elements out there. For a single-IC type of device, the
old Motorola MC1350 (8-pin DIP) is a sort-of Gilbert Cell arrangement
inside, differential-in, differntial-out, constant parallel Z-in of 5 KOhm
in parallel with a couple pFd each input. The gain control portion is
done by "starving" or actually redirecting the DC emitter current in the
input differential pair. Jameco (www.jameco.com) still sells this IC
at around $1.20 (?) in singles and has a copy of the Motorola data
for download on their website. That datasheet has a schematic of the
insides. That's good up into mid-VHF.

Some of the older JFETs had non-linear source-drain curves v. gate
voltage curves...see the difference in biasing for "depletion" and
"enhancement" mode operation. I don't know if they will work to
the top of HF range, though.


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... :-)

The voltage gain of an effective regenerative stage is can be as high
as 100,000 as reported by Charles Kitchin. That's 100dB...not many op
amps have that kind of gain at say 10MHz.

I was suggesting using op-amp ICs WITH positive feedback. :-)

I'm just not going to buy "100 db voltage gain" in a regen based on
my own experiences...unless I see the bench layout and check the
calibration stickers on the test equipment determining this. :-)

Frankly, to get a simple receiver for HF, the Tayloe Mixer and its
separate LO followed by a low-noise AF range op-amp has the
most sensitivity for the fewest parts...and with little possibility of
re-radiating the oscillations of a regenerative due to a twitch of the
regeneration control. As a direct-conversion receiver, it can handle
CW or SSB and, with a stable LO, can take in conventional AM
with a lot less tweaking than a regen with a touchy regen control.

The most stable regen I ever built (three in all, the first using that
1T4) was with a 117N7 beam-power pentode and rectifier diode, AF
out driving an old, old high-impedance dynamic speaker. Plate curves
of that tube were of the sharp-cutoff variety. AM BC band, not much
else to listen to for entertainment in 1948. I suspect it was acting
more like a "plate detector" but it had the sensitivity of a common
"all-American-five" AM table top radio receiver.

Some of the minimal-tube-complement receiver designs of older times
used regenerative detectors at the IF for sensitivity improvement. I
know of one old Hallicrafters S-38 (?) reworked that way. That receiver
had essentially an "all-American-five" tube lineup and no power
transformer. Somewhat unsafe, but useable.

Nostalgia isn't what it used to be...

Len Anderson
retired (from regular hours) electronic engineer person

In article ,
(Bruce Kizerian) writes:

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.

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 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?"

Here, I was speaking in more general terms and not referring to
regenerative circuits.

If you are speaking in general terms then there are plenty of gain-
control elements out there. For a single-IC type of device, the
old Motorola MC1350 (8-pin DIP) is a sort-of Gilbert Cell arrangement
inside, differential-in, differntial-out, constant parallel Z-in of 5 KOhm
in parallel with a couple pFd each input. The gain control portion is
done by "starving" or actually redirecting the DC emitter current in the
input differential pair. Jameco (www.jameco.com) still sells this IC
at around $1.20 (?) in singles and has a copy of the Motorola data
for download on their website. That datasheet has a schematic of the
insides. That's good up into mid-VHF.

Some of the older JFETs had non-linear source-drain curves v. gate
voltage curves...see the difference in biasing for "depletion" and
"enhancement" mode operation. I don't know if they will work to
the top of HF range, though.


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... :-)

The voltage gain of an effective regenerative stage is can be as high
as 100,000 as reported by Charles Kitchin. That's 100dB...not many op
amps have that kind of gain at say 10MHz.

I was suggesting using op-amp ICs WITH positive feedback. :-)

I'm just not going to buy "100 db voltage gain" in a regen based on
my own experiences...unless I see the bench layout and check the
calibration stickers on the test equipment determining this. :-)

Frankly, to get a simple receiver for HF, the Tayloe Mixer and its
separate LO followed by a low-noise AF range op-amp has the
most sensitivity for the fewest parts...and with little possibility of
re-radiating the oscillations of a regenerative due to a twitch of the
regeneration control. As a direct-conversion receiver, it can handle
CW or SSB and, with a stable LO, can take in conventional AM
with a lot less tweaking than a regen with a touchy regen control.

The most stable regen I ever built (three in all, the first using that
1T4) was with a 117N7 beam-power pentode and rectifier diode, AF
out driving an old, old high-impedance dynamic speaker. Plate curves
of that tube were of the sharp-cutoff variety. AM BC band, not much
else to listen to for entertainment in 1948. I suspect it was acting
more like a "plate detector" but it had the sensitivity of a common
"all-American-five" AM table top radio receiver.

Some of the minimal-tube-complement receiver designs of older times
used regenerative detectors at the IF for sensitivity improvement. I
know of one old Hallicrafters S-38 (?) reworked that way. That receiver
had essentially an "all-American-five" tube lineup and no power
transformer. Somewhat unsafe, but useable.

Nostalgia isn't what it used to be...

Len Anderson
retired (from regular hours) electronic engineer person

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


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.

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 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?"

Here, I was speaking in more general terms and not referring to
regenerative circuits.


If you are speaking in general terms then there are plenty of gain-
control elements out there. For a single-IC type of device, the
old Motorola MC1350 (8-pin DIP) is a sort-of Gilbert Cell arrangement
inside, differential-in, differntial-out, constant parallel Z-in of 5 KOhm
in parallel with a couple pFd each input. The gain control portion is
done by "starving" or actually redirecting the DC emitter current in the
input differential pair. Jameco (www.jameco.com) still sells this IC
at around $1.20 (?) in singles and has a copy of the Motorola data
for download on their website. That datasheet has a schematic of the
insides. That's good up into mid-VHF.

Some of the older JFETs had non-linear source-drain curves v. gate
voltage curves...see the difference in biasing for "depletion" and
"enhancement" mode operation. I don't know if they will work to
the top of HF range, though.



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... :-)

The voltage gain of an effective regenerative stage is can be as high
as 100,000 as reported by Charles Kitchin. That's 100dB...not many op
amps have that kind of gain at say 10MHz.


I was suggesting using op-amp ICs WITH positive feedback. :-)

I'm just not going to buy "100 db voltage gain" in a regen based on
my own experiences...unless I see the bench layout and check the
calibration stickers on the test equipment determining this. :-)

Frankly, to get a simple receiver for HF, the Tayloe Mixer and its
separate LO followed by a low-noise AF range op-amp has the
most sensitivity for the fewest parts...and with little possibility of
re-radiating the oscillations of a regenerative due to a twitch of the
regeneration control. As a direct-conversion receiver, it can handle
CW or SSB and, with a stable LO, can take in conventional AM
with a lot less tweaking than a regen with a touchy regen control.

The most stable regen I ever built (three in all, the first using that
1T4) was with a 117N7 beam-power pentode and rectifier diode, AF
out driving an old, old high-impedance dynamic speaker. Plate curves
of that tube were of the sharp-cutoff variety. AM BC band, not much
else to listen to for entertainment in 1948. I suspect it was acting
more like a "plate detector" but it had the sensitivity of a common
"all-American-five" AM table top radio receiver.

Some of the minimal-tube-complement receiver designs of older times
used regenerative detectors at the IF for sensitivity improvement. I
know of one old Hallicrafters S-38 (?) reworked that way. That receiver
had essentially an "all-American-five" tube lineup and no power
transformer. Somewhat unsafe, but useable.

Nostalgia isn't what it used to be...

Len Anderson
retired (from regular hours) electronic engineer person

IIRC the original nation sw-3 used a remote cutoff tetrode as the
regen detector, with a remote cutoff tetrode as the rf stage.
Of course they were first referred to as "supercontrol" tubes.

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


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.

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 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?"

Here, I was speaking in more general terms and not referring to
regenerative circuits.


If you are speaking in general terms then there are plenty of gain-
control elements out there. For a single-IC type of device, the
old Motorola MC1350 (8-pin DIP) is a sort-of Gilbert Cell arrangement
inside, differential-in, differntial-out, constant parallel Z-in of 5 KOhm
in parallel with a couple pFd each input. The gain control portion is
done by "starving" or actually redirecting the DC emitter current in the
input differential pair. Jameco (www.jameco.com) still sells this IC
at around $1.20 (?) in singles and has a copy of the Motorola data
for download on their website. That datasheet has a schematic of the
insides. That's good up into mid-VHF.

Some of the older JFETs had non-linear source-drain curves v. gate
voltage curves...see the difference in biasing for "depletion" and
"enhancement" mode operation. I don't know if they will work to
the top of HF range, though.



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... :-)

The voltage gain of an effective regenerative stage is can be as high
as 100,000 as reported by Charles Kitchin. That's 100dB...not many op
amps have that kind of gain at say 10MHz.


I was suggesting using op-amp ICs WITH positive feedback. :-)

I'm just not going to buy "100 db voltage gain" in a regen based on
my own experiences...unless I see the bench layout and check the
calibration stickers on the test equipment determining this. :-)

Frankly, to get a simple receiver for HF, the Tayloe Mixer and its
separate LO followed by a low-noise AF range op-amp has the
most sensitivity for the fewest parts...and with little possibility of
re-radiating the oscillations of a regenerative due to a twitch of the
regeneration control. As a direct-conversion receiver, it can handle
CW or SSB and, with a stable LO, can take in conventional AM
with a lot less tweaking than a regen with a touchy regen control.

The most stable regen I ever built (three in all, the first using that
1T4) was with a 117N7 beam-power pentode and rectifier diode, AF
out driving an old, old high-impedance dynamic speaker. Plate curves
of that tube were of the sharp-cutoff variety. AM BC band, not much
else to listen to for entertainment in 1948. I suspect it was acting
more like a "plate detector" but it had the sensitivity of a common
"all-American-five" AM table top radio receiver.

Some of the minimal-tube-complement receiver designs of older times
used regenerative detectors at the IF for sensitivity improvement. I
know of one old Hallicrafters S-38 (?) reworked that way. That receiver
had essentially an "all-American-five" tube lineup and no power
transformer. Somewhat unsafe, but useable.

Nostalgia isn't what it used to be...

Len Anderson
retired (from regular hours) electronic engineer person

IIRC the original nation sw-3 used a remote cutoff tetrode as the
regen detector, with a remote cutoff tetrode as the rf stage.
Of course they were first referred to as "supercontrol" tubes.

(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