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Old 5th Dec 2017, 8:11 pm   #33
Neil Purling
Nonode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,083
Default Re: Two or three IF stage Chinese radio kits.

My previous post was referring to the HX-6B, the S66D and the 9018-2. They are all the same circuit. The diagram you get with the HX-6B only gives 0.5 mA as the current one should see at measurement point 'B'. I was seeing more than that, but that break is related to V2. Nothing to do with V3 & my experiments altering R4.
The given 30K for R4 would give maximum signal? I don't quite understand what is going on there. I did have a 100 K trim pot as R4 on another board. I measured the resistance after extracting it & found it to be 89K. The output of the detector was not that strong.
I assume that one would adjust R4 on the basis of noting any distortion if the o/p to the speaker were 'scoped. The adjustment of R4 would change the strength of the AGC level and thus what signal is being amplified.
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