High Stability Oscillator Units Type HSO         All photos copyright John Mills, last updated 28 Dec 2009 This range of temperature-compensated oscillator units will find a wide application wherever exceptional oscillator frequency stability is required, such as for VFO units, beat frequency oscillators, conversion oscillators and sideband selection, without incurring the expense of crystals. Each unit is completely self-contained with all the associated oscillator components incorporated within a small aluminium can 0.75" sq x 1.375" high. Three negative temperature co-efficient close-tolerance condensers and a grid leak are arranged around a special oscillator coil which is wound on a Phenolic former and impregnated with polystyrene. Any small triode, such as a 6C4, or half of any twin triode can be used, or the triode section of a frequency changer, or the cathode, grid and screen grid electrodes of a pentode valve. The only external components required are a suitable anode load resistor and variable pitch control tuning condenser for the BFO units; an anode load resistor for the CIO units; and for VFO use, a dial tuning condenser plus the anode load. For sideband selection a single pole, 2-way or 3-way switch and suitable values for Cx, plus the anode load resistor is all that is needed. However, for the ideal heterodyne detector circuit see fig. D which is similar to that in the G2DAF Rx design but with the added advantage of variable BFO facilities. The anode load should consist of a carbon resistor between 10K ohm and 50K ohm, depending upon the RF output voltage required.   The circuit arrangement consists of very large lump Cs of up to 200pFs across the anode and grid of the triode, with a series tuned circuit between, the frequency of which is adjusted by an iron dust core having a hexagonal hole, for adjustment by our nylon trimming tool. The complete assembly is enclosed in a PVC sleeve, and held in an aluminium can at the top by our standard toughened polystyrene fixing screw and washer, and by two 6BA ¼" screws at the base of the can, these two screws also serving to clamp the units to the chassis.   A 105v or 150v stabilised HT supply must be used for max. frequency stability, but as the current is so low the HT feed can normally be taken from the stabilised HT supply feeding any other stage in the Rx. RF output from these units can be taken via a small C from either the grid or anode, depending on the injection voltage required by the associated circuits   Click the image below to view all circuits referred to in the chart below:   Circuit Diagram Type Max 'L' C1 C2 C3 C4 R1 Freq Coverage FIG. HSO50 15mH 2000 2000 2000 100pF 100k 47 to 53 Kc/s A HSO85 10mH 1100 1100 1100 75pF 100k 80 to 90 Kc/s A HSO100 9mH 1000 1000 1000 75pF 100k 95 to 105 Kc/s A HSO350 760µH 1100 650 1100 - 50k 330 to 415 Kc/s C HSO460 610µH 1100 430 1100 50pF 50k 410 to 515 Kc/s B HSO550 760µH 1100 270 1100 - 50k 470 to 600 Kc/s C HSO1.1 120µH 650 430 650 - 33k 1.05 to 1.25 Mc/s C HSO1.6 79µH 650 270 650 25pF 33k 1.45 to 1.75 Mc/s B HSO2.1 51µH 650 270 650 - 33k 1.75 to 2.15 Mc/s C HSO3.0 17µH 540 270 540 75pF 33k 3.0 to 3.5 Mc/s A VFO2.0 45µH 650 270 650 75pF 33k 1.8 to 2.0 Mc/s A VFO4.0 14µH 540 270 540 100pF 33k 3.5 to 4.0 Mc/s A VFO7.0 5.5µH 430 134 430 25pF 33k 7.0 to 7.45 Mc/s A If using Fig. E increase capacity of C4 by approximately 25%   Thanks go to Ron Bryan for his help on providing the data for this page   MODEL Used as a BFO with Pitch Control Used as a Conversion Oscillator HSO50 For 50 Kc/s IF n/a HSO85 For 85 Kc/s IF n/a HSO100 For 100 Kc/s IF n/a HSO350 n/a 440-480 Kc/s IF to 50-100 Kc/s IF amp HSO460 For 440/480 Kc/s IF n/a HSO550 n/a 440-480 Kc/s IF to 50-100 Kc/s IF amp HSO1.1 n/a 1.62 Mc/s IF to 440-480 Kc/s IF amp HSO1.6 For 1.62 Mc/s IF 1.62 Mc/s IF to 50-100 Kc/s IF amp HSO2.1 n/a 1.62 Mc/s IF to 440-480 Kc/s IF amp HSO1.1 n/a n/a Typical Application VFO2.0 160m VFO tuned by 75pF = Fig. A. 100pF = fig. E VFO4.0 80m VFO tuned by 100pF = Fig. A. 125pF = fig. E VFO7.0 40m VFO tuned by 20pF = Fig. A. 30pF = fig. E HSO3.0 SSB VFO in G2DAF T/X tuned by 75 pF