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2496 |
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| A low noise, AF voltage amplifying pentode specifically for very small signal preamplifier applications. It features an all enclosing, outer screen or shield around all electrodes, special measures for extra mechanical stability against microphony, and a bifilar wound heater element to reduce hum injection to the absolute minimum. Open loop gain can exceed 40dB, with both white noise and hum down to typically 2╡V at the anode (heater supply must be balanced and centre tapped to 0V near the valve, or DC). Especially suited to first stage amplification of magnetic cartridge (phono) and playback tape head inputs. Pins 2 or 7 (screen) should be grounded to 0V. |
| Mullard recommended circuits |
| There is basically just one recommended circuit configuration for the EF86 (shown in more detail in the data booklet). In this only two variations for resistor values are advised, as follows: |
| Anode load resistor |
100k |
220k |
| Screen grid (g2) resistor |
390k |
1M |
| Cathode bias resistor |
1k |
|
2k2 |
| In each case the cathode bias resistor should be boot-strapped to 0V with a 47╡F 50V electrolytic. The grid leak resistor (g1) can be 1M or less (usually chosen to match the sending transducer). The suppressor grid (g3) normally connects directly to the cathode. |
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