I was wondering if ya'll could help me with an issue that I am having
with a regen receiver that I built.

I built the usual regen circuit with two stages of audio coupled with
interstage transformers. The regeneration is controlled by a pot which
varies the plate regen voltage. The grid leak combination is a 6 Mohm
resistor and 45 pf cap.

The regen and first audio stage tubes are 1H5GT triodes. The second
stage audio tube is a 1C5GT pentode. The filament voltage is 1.4
volts, plate voltage is 90 volts and screen voltage for the 1C6GT tube
is 90 volts. The set easily and cleanly drives a speaker.

I have wound my own coils which cover the broadcast band up to about 15
Mhz.

I really like the way the set operates and it is very sensitive.

My problem is that the regeneration often fades out (the radio
essentially goes dead) and I have to touch the grid of the regen tube
to bring it back in. I had originally built this radio only having one
stage of audio and I did not have this problem with that version. It's
kind of like the charge on the grid builds up too high and I have to
"drain" it off with my finger. Sorry for the bad description--I'm
obviously not an engineer.

I did try various other combinations of the resistor/cap for the grid
leak including the classic 2.2 Mohm/150 Pf combination and it still has
the same fade out problem. Therefore,
I decided to stay with the higher resistor/lower cap value because the
receiver works better at those values (when it is working).

I usually power the radio with a battery eliminator, but the same
problem exists even when I use only batteries. For a ground, I am
using the mains ground.

I'm hoping that you can give me some ideas to fix the problem for what
is otherwise a great receiver.

Thanks to all of you in advance.

Dan

Hi Dan,

Have you checked that your 6M ohm grid leak is actually 6M ?

It does sound like a charge build up on the grid. Does the RF anode
current rise or fall when the radio goes dead ?

Are there any components attached to the grid that could be breaking
down slowly - capacitor, maybe even valve base.

Have you tried replacing the valve base ?

Have you tried a different valve ? Maybe broken or cracked valve bottom
(paxolin to valve pin).

Stick the whole unit in the oven (on low) and dry it out for 3 hrs -
moisture getting in somewhere ?

Does sound weird and interesting.

Regards,

Mark.

Hi Mark,

The resistor is definetly 6 Mohm, but you bring up an interesting point
about moisture.

I have noticed that the set seems to fade out more during rainy or high
humidity days. I didn't even want to mention it because it sounded
silly, but I did wonder if humidity might be a factor.

On some clear, dry days, I have not had any trouble at all. So, maybe
you have something there.

I will carefully go back over the items you mentioned and maybe replace
all of the caps in the circuit. Replacing tubes hasn't made a
difference. Thanks.

Dan wrote that the regeneration in his receiver is controlled by a pot
which varies the plate regen voltage. I saw this method was popular
mainly in old books (ARRL from 30's and 40's for example) but later the
most popular became a control on the screen grid. Does it mean, that
the second method is better ? Why ?
Sorry if my question is naive but I'm beginner, especially in tube
stuff.

"Dan wrote that the regeneration in his receiver is controlled by a
pot
which varies the plate regen voltage. I saw this method was popular
mainly in old books (ARRL from 30's and 40's for example) but later the
most popular became a control on the screen grid. Does it mean, that
the second method is better ? Why ?
Sorry if my question is naive but I'm beginner, especially in tube
stuff. "

Actually my regen tube is a high mu triode (1H5GT), so there is no
screen voltage to control. A lot of folks like to use throttle caps to
control regen, but pots are easier to mount and don't take up quite as
much space. (I know that a lot of people will disagree with me here on
my choice).

My second audio tube is a pentode (1C5GT) and I use a one meg pot on
the grid to control the volume for the set. I also have a 10 ohm pot
on the first audio tube (1H5GT) filament which also helps control the
volume and nulls out hum.

In case you are wondering why I chose these tubes, they are the tubes
that were used in the old battery sets and have low battery drain
(although I use a battery eliminator anyway for my power source). They
are also very cheap and plentiful.

I also was able to "steal" the engineering from the old battery radio
schematics to figure out the capacitors and resistors to use in the
audio circuits to make the output sound good. I'm basically too lazy
to learn the formulas to do my own calculations. The set sounds as
good as any battery set that I have ever heard.

This particular combination of a 1H5GT first audio stage tube followed
by a 1C5GT second audio tube was used in a lot of battery sets. It
also made selecting the output transformer easy to maximize output to a
4 ohm speaker.

Dan

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 ?