This home-brew 14 tube HF ham bands receiver was built by an unknown amateur radio (ham) operator (but see below on possible builder). Build date was probably in the mid to late 1950's. I was immediately attracted to the piece because of its classic PW tuning dial as found on the National HRO receivers. Construction is excellent and includes engraved control markings on the front panel. Bandswitch has 3 positions marked 15-10, 80-20, and 40. Controls are RF gain (left of the bandswitch), "audio" (volume, on right of bandswitch) The unlabeled control (bright metal knob) switches in the product detector. Toggle switches are for power and standby. Phone jack labeled "output" is for headphones or external speaker. That jack is repeated on the rear of chassis. Upper right controls are "AVC-MVC-CW" and "CW OSC" (BFO). The IF transformers are likely from a BC-312/342 and the audio output transformer also appears to be military surplus. Most other components were new when the set was built.
The three band converter on the extreme left has 10.5, 17.5, and 24.5 MHz crystals. Tubes in converter are 6C4 oscillator and a 5670 as RF amp and mixer. Bottom control selects among 10, 15, 20 and an unlabeled position to switch out the converter for 80 and 40 meters. The converter variable is for RF preselection. Tubes at the back of the chassis are a pair of 6K7 for IF, a 6H6 for detector, and 6SJ7 for BFO. Tubes to the left of the 3 section main variable top to bottom are 6BZ6 RF amp, 6BA7 mixer, and 6AH6 oscillator. Tubes to the right are 12AU7 for product detector and a 6SJ7 and 6V6 for audio. Rectifier is 5Y3 with 0B2 as voltage regulator.
Did the usual thorough cleaning, safety testing, and application of deoxit on the controls and tube socket pins. Found the PW dial too stiff in operation. Opening its gear box and lubricating solved that problem. The set worked but the 40 meter band was dead. The problem was traced to an OPEN oscillator trimmer. Deoxit did not help. These trimmers are in series with the main variable cap so that precise bandspread can be achieved. Using the frequency counter, the open trimmer resulted in so little capacitance that the variable cap only changed the oscillator by one KHz or so. The edge of the trimmer can be seen in the bandswitch shield box at the extreme lower left of that box.
Found a nearly identical trimmer in my "boxe de junque". Because the builder had gone to considerable lengths to shield the circuits, had considerable difficulty removing the bad trimmer and inserting the replacement but managed the task. Aligning the replacement trimmer, tweaking the other trimmers, and re-setting the PW dial resulted in a very sensitive and stable receiver. An excellent example of quality homebrew art of the 1950s.
Attempts to identify the set.
Circuit? Schematic? Article?
Given the nice circuit design and the thorough craftmanship, I found it difficult to believe that this receiver was totally unique. If you recognize this set from some article in QST or other publication, please let me know.
Information received from the net regarding possible builder
One response received indicated that the set may have been the work of Harold Bourell, W6NZ, based upon the workmanship and general layout. The responder who was himself a recipient of one of W6NZ's homebrew transmitters says, "Harold was one of the great masters of the homebrew art". Describing the transmitter and W6NZ's workmanship, he continues,
I received a call from Gary NJ8BB from whom I had purchased the radio at the Columbus, Ohio hamfest in August 2003. He indicated that he had purchased the radio in 1984 at a radio club auction in Long Beach, California. Gary served as radioman aboard the battleship New Jersey. According to Gary's recollection, the former owner was identified by the Long Beach club members as Harry or Harold. The opinion that this radio is the work of Harold Bourell, W6NZ is therefore, given further credence.
Let me know if you can shed further light on this receiver's origin.
An old homebrew amp with two 813 tubes and a new-brew junk-parts power supply
were the previous items on the bench.