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Building a regen set from scratch can be quite an undertaking for some.
Gathering the rf parts in itself can be expensive and cause big wrist problems from
all that clicking on eBay auctions. Then getting the coils right can take hours and after that
you have to try to calibrate the dial. Then usually you end up with a 0-100 scale.
If you like building circuits but are ending up pounding your head against the wall, maybe
a project like this is for you.
An old time signal generator can make a nice tube regen radio. The oscillator
section can be made into a regenerative detector with very little effort. Other advantages
of a conversion over a new build is that most of the parts are mounted, the power
supply is built and the chassis work is done. For this project, no drilling
was required, except for the speaker I mounted inside the box (right hand side).
I did the my conversion on an Eico 315 signal generator that was in very good
condition. Many other signal generators will convert. I liked this one because it looked easy
to work on. The dial scale is large. The tuning is very smooth and geared down. The
circuit had enough stages so that I could build a good radio.
To convert a signal generator to a regen radio first need a plan. Go to the
BAMA site and find the manual for the generator
you are considering converting. If you already have the generator, make sure it is
working before you tear into it. Check the dial for backlash and how easy it is to
tune. Take a look and see if you can get at everything you need to. Try to avoid
contact with the coils and tuning system that is in place. Check for enough
holes in the front panel to mount the controls you need. Besides the main tuning,
and band switch, you need a hole for the rf input, speaker, input attenuation,
regen control. Fine tuning and volume controls are also good but not necessary. I left
out the volume control in my conversion.
After you have your conversion plan, you need to take out what isn't needed
and then build the circuits around what you have.
The more tube sections, the better the radio you can build. The Eico 315 has
three triodes. My conversion is built around my successful
Regen-O-Flex radio, built in 2004.
After removing all the parts that aren't needed, it is time to make this
thing work. The resistor in the oscillator grid was changed to a 1.5 meg ohm value.
The plate circuit was reworked so the voltage is obtained from a 50k pot.
This is the regeneration control. A 68 k resistor was placed at the top end of
the pot and connected to the 150 stabilized supply.
The 6SL7 which was the original modulator and cathode follower output
is now a reflex rf / af amplifier and a one tube audio amplifier. The audio
amplifier has a small output transformer that couples the audio to the speaker.
The supply voltage for this stage is about 180 volts. The audio output is very
reasonable for a small triode stage.
The other tube section is first a grounded grid rf amplifier and a
grid driven audio amplifier. This circuit worked very well in the Regen-O-Flex
radio. RF energy from the detector won't be radiated by the antenna because
of this stage. By the double use as an AF amplifier, the levels are boosted
for the audio output stage.
All the parts for this conversion were from my junk box alone. I tried
to use what was already with the generator. I added a small variable capacitor
as a fine tuning control. I didn't want to change the outside appearance by
much, so all existing holes were used and no new ones were added.
After you finish your conversion and are happy with everything, it is
time to align the receiver. The air trimmers are mounted on the side. The
alignment should be done by picking a calibration point near the top of
each band. My radio doesn't work on the F-G bands. I'm not sure why but
I am not worried about it. The alignment should be done with the bandspread
fine tuning capacitor at the minimum value.
My first listen was a station on 40 cw working dx. I was happy to
observe that there was very little drift with this radio. That is another
advantage of using LC circuits already built.
Check the schematics below and see how they compare with what you have.
Please don't ask me for specific design information on other signal generators.
I may do more of these but only if the generator generates above average
interest. I do have an Eico 324 that I might convert. It has enough tube
sections but the power supply isn't that great.
I spent less than 6 hours designing and converting this generator
to a cool radio. That was a lot less than if I had started from scratch.
So if you have one of these boxes laying around, consider putting it
to use as a little radio. This project should be attempted by someone that
can work with several hundred volt circuits without being careless. Nothing
ruins your day more than being knocked on your can because you forgot to
unplug before working on a project.
Happy building de N2DS!
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