[Boatanchors] My Homebrewed Regen Receiver project, link to pictures

[Ray, W4BYG]

Great project and congratulations on getting it going.  But I question 
the ready availability in the 30's of the miniature tubes and the 
ceramic magnet speaker.

Ray, W4BYG


On 2/12/2016 3:16 PM, Phil wrote:
> On my Beacon mail list it was requested that I post (actually re-post) 
> the information on the tube type regen receiver I designed/built this 
> past summer.  I thought it might be of interest to some folks here. . .
> **************************************
> Good Mornin' (afternoon for you) Václav
>
> Thank you for asking about my receiver.  No manual, no schematic. When 
> I designed/built it, I first sat down and figured out exactly what I 
> wanted it to do, specifically be an above average regen designed for 
> NDB DXing.  A real tool, not a 1 or two tube 'novelty' set that would 
> sit on the shelf and not be used.  The ability to work other bands if 
> desired was also on the list, which dictated the use of plug-in 
> coils.  More CW selectivity than a regen usually has, and the ability 
> to drive either a speaker or modern low impedance headphones were also 
> desired.  BUT MOST IMPORTANT TO ME, I wanted the set to be based 
> ENTIRELY on technology available to the experimenter in the 1930's, NO 
> solid state active stages.  I DID use silicon rectifiers in the PS 
> simply because the transformer I used wouldn't support rectifier tube 
> filaments etc.
>
> Then I drew up a basic block diagram, knowing that the exact circuit 
> would depend heavily on what electronic components I could obtain. So 
> at this stage I didn't draw any schematics, but came up with a basic 
> list of parts that I would need.
>
> As project cost was going to be expensive IF I had to buy everything 
> new, I then went on a scavenger hunt to see what I could scrounge up.  
> I put a want list in our local ham radio newsletter, as well as some 
> of the vintage radio and boatanchor mail lists I belong to, wanting to 
> purchase old parts.  Things like tube sockets, power transformer, 
> audio output transformer, tuning capacitor and so forth.
>
> This paid off nicely in a quite unexpected way.  A man in Washington 
> State offered me some adjustable 10H audio chokes, suitable for a 
> 'passive' audio CW filter.  Sent me three of them and they immediately 
> became the components around which the entire receiver was designed.  
> With capacitors they would form a parallel resonant circuit.  They 
> were tapped allowing  the filter to have a low input impedance (plate) 
> and high output impedance (grid of next stage). He also sent me an 
> Emmco vernier tuning dial from the 1920's.
>
> An almost local ham friend told me had a lot of stuff on my list, 
> tubes, tube sockets, power and output transformers, old military style 
> black Bakelite knobs, potentiometers, etc, free for pick-up. Needless 
> to say I drove the ~30 miles to get them.
>
> Now things were starting to come together (this was a long summer 
> project, NOT one to quickly complete).   I took the stuff that I had 
> gathered and laid them out on the workbench to get an idea of what 
> sized chassis I would need.  For rigidity/stability a good aluminum 
> chassis was important.  I ended up buying one that was 12x8 inches 
> along with two aluminum bottom covers (one to use as a front panel).  
> I thought it might be a bit large for the project, but in the end 
> turned out to be the perfect size.  At about $50 it was also the 
> single most expensive item in the project, but I felt a necessity .
>
> Once I had everything on hand I hand drew up the basic schematic of 
> each stage, knowing that some of the circuits would be tweaked once I 
> got the set working.
>
> Next step was to set  all the major components on the chassis to 
> figure out the best layout.  Important to keep the RF amp and detector 
> stages as far as possible from the power supply (regen detectors are 
> prone to hum pickup).
>
> NOT a single hole was cut until I felt I had a good layout.  I then 
> drilled all the holes for the tube sockets, controls, transformers 
> etc.  NOTE:  Not having any Greenlee chassis punches like I had as a 
> kid in the '50s (they're VERY expensive now) I was told that a step 
> drill like Harbor Freight sells is a VERY good, and possibly superior 
> alternative.  Reasonable in cost, effective, I now have five of them 
> in different sizes, from a small 1/8" to a large 1-3/8".  I even sent 
> a couple to another member of this list so he could punch some tube 
> socket holes.
>
> I even drilled the holes to mount the Emmco tuning dial.  NOTE: After 
> I built the set  I found that even with a lot of tweaking, lubrication 
> etc, with it's relatively small tuning knob the dial was a bit too 
> stiff to allow my arthritic fingers to tune it for long periods of 
> time (remember, I said this radio was being built as a serious DXing 
> tool).  So I ordered a couple used National Vernier Reduction Drives 
> from surplus WWII equipment and installed one. MUCH better and 
> smoother, meant I had to enlarge the mounting hole and relocate the 
> tuning capacitor slightly. . .
>
> OK, I won't go into detail about how each stage was tweaked as I went 
> along.  But here's a description of each stage and what it does, 
> following signal flow through the set.
>
> 1.  6AK5 tube, untuned Grounded Grid RF amplifier.  Not there for 
> gain, but to isolate the antenna from the following detector stage. A 
> regen detector has high gain and easily overloads.  The RF gain 
> control is a Potentiometer in the cathode input circuit. There is also 
> a 580KHz wavetrap at the cathode as 580 KMJ in Fresno (a 50kW station 
> about 60 miles away) tended to bleed through on the high end of the 
> NDB band.
>
> 2.  1/2 12AU7 dual triode.  Armstrong Regen detector stage.  The 
> classic regen detector with tuned grid coil and a tickler coil in the 
> plate circuit.  Some other circuits, such as a Colpitts or Hartley 
> were suggested to me on the Regen mail list, but I settled on the 
> classic Armstrong circuit.  Some folks have had problems with the 
> circuit smoothly going into oscillation, but mine works VERY well 
> (think it depends on the exact circuit parameters as to how smooth it 
> is).  This one is also EXTREMELY stable, after a short warmup of a few 
> minutes, in oscillating mode it NEVER drifts more than a hundred Hz or 
> so.  NOT at all bad for a tube type free running oscillator!!!  Of 
> course this is at LF, it would probably be a different story at HF and 
> above frequencies.
>
> 3.  1/2 12AU7 dual triode.  Cathode follower loosely coupled to the 
> plate of the Detector tube.  It's output feeds a BNC connector on the 
> back panel so that an external frequency counter can measure the 
> actual receiver frequency when the detector is oscillating.  NOT 
> really out of the spirit of designing the set with '30s technology as 
> it doesn't have any effect on how the set itself performs.  It's there 
> to facilitate dial calibration or to quickly tune the set to a desired 
> frequency.  I rarely use it in actual listening as it only works when 
> the set is strongly oscillating, otherwise the counter just bounces 
> around.
>
> 4.  1/2 12AT7 dual triode.  First audio stage, audio filter driver. 
> Not a lot to say about this one, it does what all audio amplifiers do, 
> and it isolates the detector stage from the audio filter stage.
>
> 5.  Passive audio stage.  This is comprised of a 6 position switch, 
> three parallel tuned circuits resonant at 400, 600 & 1020 Hz, and two 
> RC Low-Pass-Filters (treble cut-off).  First position bypasses all 
> audio filtering, but I never listen in that "wide" position.  Most of 
> my listening is in the narrowest LPF position (treble-cut), switching 
> to one of the bandpass filters when needed.   The audio filtering is 
> VERY effective in digging out weak beacons.
>
> 6.  1/2 12AT7 dual triode.  2nd audio amplifier stage brings the audio 
> level back up after the losses introduced by the audio filters.  The 
> volume control is located between the audio filter and this stage.  
> The set was intentionally designed with more AF gain than needed.  At 
> first the volume control was between the detector and first audio 
> stages, but hum from the audio chokes in the filter was objectionable, 
> especially in the headphones.  Even though the chokes are in a 
> shielded steel box, they still get 'some' hum from the nearby power 
> transformer.  Changing the gain distribution in the set by relocating 
> the volume control completely removed it.
>
> 7.  6AQ5 audio output stage.  Again, this section does just what it 
> should, provide sufficient power to drive a speaker or modern headphones.
>
> 8.  0B2 Voltage regulator tube.  Provides a stable 105 Volts to both 
> the RF amplifier and detector stages.  This is probably one of the 
> contributors to the excellent stability of the receiver!
>
> 9.  Rectifier stage.  Uses 4 1N4007 diodes in a bridge configuration.  
> My one concession to modern electronics in the set. The 'donated' 
> transformer did NOT allow for a full wave tube rectifier, but I wanted 
> full wave rectification as it is much easier to filter 120Hz than it 
> is 60Hz.  There is also a large DC filter choke in the B+ filtering 
> circuit and VERY heavy filtering via the over-sized filter 
> capacitors.  That along with the 0B2 regulator means that the DC 
> supplied to the radio is essentially "battery pure".
>
> 10.  Filament circuit.  As I mentioned, regen receivers are prone to 
> hum and noise, often coupled from the filaments of the tubes. Part of 
> the problem is that one side of the filament circuit often uses the 
> chassis as a conductor, a bad design.
>
> In this set I floated both sides of the 6.3 Volt filaments above 
> ground, wiring with twisted wires.  At the 12AU7 tube, both sides of 
> the filament line is bypassed to ground with capacitors.  In addition, 
> there is a 100 Ohm pot wired across the filament lines, and the wiper 
> is connected to the chassis ground.  This is a "hum balance" control 
> and is common in many older audio amplifier designs.    The result is 
> that between the well filtered B+ and the design of the filament 
> circuit, there is NO audible hum in the receiver at all (outside of 
> the aforementioned bit from the audio filter chokes, now almost 
> completely gone).
>
> FINAL NOTE:  I've been asked a number of times if I'd draw up a 
> schematic, and somebody suggested using "tubepad" software to do it.  
> I've wanted to, need to locate the software, THEN FIND THE TIME TO DO IT
>
> Pictures of the radio may be found here. . .  You do NOT need a 
> Photobucket membership to view/download the files.
> http://s38.photobucket.com/user/ko6bb/library/Tube%20Type%20LF%20Regenerative%20Receiver 
>
>


-- 
I'm no longer young enough to know everything!