Saturday, 5 December 2009

AF Pre-Amp

Back to some more work on the radio receiver - Harry specifies an additional gain stage before the final EL84 output. The stage uses half of a double triode - in this case an ECC81 (/12AT7).

Before doing anything more, the pin-out of the tube is as shown in the figure below...


Harry's schematic (seen complete on his excellent website - be sure to use his updated address) is reproduced in "edited" form below, to show just the single AF Pre-Amplifier...

This stage was simple to build - I described the enclosure last week and I did all the hardcore metalwork - so this stage involved no significant mechanical engineering !

I took the opportunity to put the inverter into a box - for convenience and safety. I used another of the "chassis" enclosures from Maplin (order code XB56). The entire system to date is shown below (couldn't resist stuffing the empty valve bases with their respective valves - although only the two on the right are "doing anything" in this picture).

Now the audio section of the radio is completed - time to get on with some higher-frequency antics...

...-.- de m0xpd

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