Hello- I am in the process of installing some upgrades in my R-4C, an early one (18K SN range) that has the 6HS6's. The INRAD 8 KC 5645 KC first IF filter was in when I bought it, so at least I have a little bit of protection for that second mixer. I upgraded the power supply with the 7812 regulator and better electrolytic caps all around, per WB4HFN info combined with Sherwood info. Today I built the IC product detector using a TL442CN, installed it and appears all is well. I thought I would post this as I believe the TL442CN is an obsolete device. The TI SN76514 is an identical chip, it was used in the Mihuzo 9 Mhz SSB boards as the balanced modulator. One thing, I am powering mine fom the +10 VDC that is provided for BFO, as that terminal was very near the module. Is itnecessary to have the full 12 VDC on the chip? I wish to do the sudio amp upgrade, mostly to get rid of the heat, but also to have a little better audio. I am thinking of going with the LM383T as done by Sherwood, but saw a video of an R-4C sporting a "D-Labs" audio upgrade. I cannot find any additional info on this. Thought I would ask for advice before I proceeded with the audio changes. Thanks, Byron WA5THJ
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