[TenTec] C21 Sidetone Mod

[Ed]

This is from an article originally written by Bob Borum KN4JJG. I had no 
luck finding him or the original article via QRZ or Google. What I have 
is a very old, almost unreadable copy of the article.

The sidetone frequency is controlled by R1 (68k) on the 80356 board. He 
suggests paralling a 47k with R1. Or you can remove R1 and use a 
variable to find a suitable value and substitute that for the original. 
I just added the 47k and that was close enough for me. Be careful, I 
have found other C21's already had changed the value of R1 to fix this 
problem.

I also have a hand written how-to on adding a pre-amp to the RX. I did 
this mod also and it made a remarkable improvement to the C21's 
sensitivity on all bands, most noticabbly on 10-15-20. This how-to is 
dated 2-13-78 and was written by Dick Frey W1FCC/K4XU then the Chief 
Engineer at Tentec. It is a decent readable copy and I will be glad to 
share a copy for an SASE. It is 4 hand written pages.

HTH.

73

Ed W3NR