The AM Forum

I spent quite a few bench hours before finally finishing up a Signal One CX-7A and after that experience I decided to plunge into something simple like a 1930's regen.  I picked up this Sargent 11-MA recently and all it needed was replacement of a number of very leaky wax paper caps.  All of the original resistors were easily in spec; they sure age better than the late 40's/50's carbon resistors.  I have a replacement glass dial cover on order from a clock company to replace the missing one which had a slight crack but otherwise the receiver is cosmetically pretty good.

The MA version (for marine) covers from 80 Kcs. up to 31.5 Mcs. and has 1 RF stage and 2 audio stages.  The most unusual aspect is the bandspread tuning.  It has only a single variable cap which is mounted in a swivel arrangement.  The main tuning dial works as expected by turning the rotor of this cap.  The bandspread dial uses a pulley and lever arrangement which causes the frame of the tuning capacitor to rotate slowly while the rotor is held in place.  I was dubious because it looks pure Rube Goldberg but after tuning in SSB signals on 20 meters I have to admit it works.  There are no calibration adjustments but it is very close, WWV comes in as expected at 5 and 10 Mcs. and is off by the two widths of the dial pointer at 2.5; of course the main dial can be calibrated via the bandspread dial.

Next on the "early receiver hit parade" are a pair of RCA receivers (ACR-136 and 175) and Hallicrafters SX-9 and SX-11.  After this I might be radio to tackle another complex SSB transceiver.

Early Hallicrafters..Drool, Slober, Drool, Drool
Must buy more.

Can you post a picture of this rotating capacitor arrangemt?
It sounds very interesting.

Bill

Bill,

The images of the tuning mechanism did not turn out well but the best of the bad is attached.  In it you can see the tuning cap at the top with a long lever going down to the bottom where it is activated by a pulley that moves on an arm attached to the band spread shaft.   Looking at the very top of the photo in front of the front cap section there is a spring which normally pulls the tuning capacitor frame to its normal rest position.  In the back of the capacitor frame is a pivot bearing inline with the capacitor thrust bearing and the frame pivots around this point.  Since the rotor plates remain fixed when the main tuning knob is not moved the stator plates in the frame now move relative to the rotor plates.  The length of the lever to the capacitor in conjunction with the geometry of the offset arm with pulley on the band spread shaft cause the capacitor frame to have only a slight rotation for a relatively large rotation of the band spread control.

When I first saw this I thought it would be a disaster but it actually tunes very smoothly.  I believe Sargent used this in several of their receivers.  Up until this point the strangest setup I had seen was that used in some of the lower cost Hallicrafters receivers where a separate rotor interacts with the main tuning capacitor to provide band spread.  

This system means all of the leads to the tuning cap have to be flexible but they seem to have withstood the test of time.

I had a Sargent 10 that I restored. It had the same set up
http://home.comcast.net/~chnord/sargent10a.htm (http://home.comcast.net/~chnord/sargent10a.htm)
(http://home.comcast.net/~chnord/Sargentad.jpg)
Pretty neat radio
Carl
/KPD

That rocker bandspread arrangement is detailed in an article about building a "Cigar Box Doerle Regen Receiver" in the Feb 2008 issue of Electric radio. It's kinda cool!

Carl,

I came across your site when I was searching for Sargent info and your model 10 looks nice.  I imagine the circuit is very similar to mine.  The only addition to mine over the years was a neatly added VR-150 tube.  It doesn't perform quite as well as my RAK and RAL regens but in terms of performance per pound and per dollar of original cost it would win.

Greg,

I will go back and take another look at that article in ER.  I remember reading it but I missed that detail.  I have a Doerle construction article from an early Radio News that I plan to use as a building plan some day.

Rodger,
  Thanks for the picture! That is a truly unique setup.

Bill