The regeneration control either varies the amount of feedback
(throttle cap, movable tickler coil, or pot across the tickler coil)
OR varies the gain of the valve (or solid state device) by varying the
plate voltage (pot or series resistor), screen voltage (consider the
screen of the tetrode or pentode as the plate of the triode and the
plate of the tetrode that of a cascaded second stage), or grid voltage
(yes you can also add negative bias to the grid to lower the gain,
rarely used in a regen using tubes but the ONLY way with FET's).

If the variable gain method is used, then the tickler coil must have
JUST the right number of turns so there is JUST the right amount of
feedback for regeneration to start when the valve (or other active
device) is operating at the optimal gain setting for detection. If
TOO much feedback is provided the gain of the detector must be set
so low that poor sensitivity results. Also adjustment of the regen
will be tricky. If too little feedback is provided regeneration may
not happen or the detector gain will have to be so high that the
detector will be unstable.

For some reason most triodes seem to operate as detectors with
about 30-50 volts on the plate, and pentodes with 20-50 volts on
the screen. Using a regulated supply for the detector is a good
idea, especially if you want to try and receive SSB signals.

The fade out problem with your regen sounds familiar, I had this problem
on an old AA5 radio. It would stop playing after a while and came back
if I touched the signal grid lead (antenna tuning cap hot side) of the
12BE6 tube (I actually held one end of a .01 cap and touched the OTHER
side of the cap to the grid as it was a hot chassis set). Weird!

Maybe I had a bad cap in the agc circuit, not sure.


wrote:
On 29 Apr 2006 06:26:08 -0700, wrote:


My mistake, it's a triode, no screen grid. I'm not used to American
symbols, here in Europe we have easier sytem (EC-triode, ECC-double
triode, etc.). For me 1H2GT and 1T4T is the same tube


What are the differences, advantages and disadvantages between methods
with a pot in plate circuit, screen grid circuit, throttle cap ?


Apples and potatoes. Seriously screen grid valves(tubes) of the
tetrode/pentatode flavor are different animals than triodes so
applying comparison of regen throttle techniques across them
is difficult to compare. However.. with that said.

Throttle cap is usally the best as you can optimize the tube operating
point and then only adjust the amount of feedback. Disadvantage is
there is RF on the capacitor and that means careful layout and good
mechanical mounting for stability.

The other two vary the plate(anode) voltage and vary the screen
grid voltage are similar as they both affect the gain of the tube by
altering it's operating point. Disadvantage is that you may have
to play more with the feedback winding (or tap) so that regeration
occurs at the best point on the variable resistor or performance will
suffer. Advantage, no RF on any of the wires to the resistor so
placement and mounting is more flexible.

Both can be made to work equally well with care.


Allison