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Wednesday, May 27, 2015

BITX DIGI-TIA Update #5: Amplifiers Built and Tested


I have the RF amplifier stages done, and I worked a bit on the shielding.  This circuit board will be along the back, turned around, with the copper-clad shields between the amps and the rest of the rig.  In the picture you can see the small inter-stage shields, and one that put between input and output on the final.  All this in the probably vain hope of avoiding the Agony of Oscillation.   We'll see.  So far so good.  I get about 8 watts out of the IRF510 on 40 meters.  53db total gain for the three stages.  Of course, all this will likely change once the rest of the rig, the LP filter and an actual antenna are added.
 
As for the mic amp problems I mentioned last time, well,  I discovered on earlier BITX projects that one of the resistors in the base circuit needs to be changed from 10K to 39K.  It is kind of a long story (maybe for the podcast) but essentially I had to discover this AGAIN.  More details here:
 

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1 comment:

  1. Thanks Bill for the comment on the mic-amp. Its a recent lesson for me, especially if you built the rig a while ago and you are troubleshooting from the schematic. Soldersmoke Rule #N : Find the latest schematic revision on the web and troubleshoot from that. How about Bill's Big Book of Homebrew troubleshooting wisdom. I'd by a copy!

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