Thursday, March 29, 2018

Norcal 40A 30A..that's "30" for tonight..

Posting WB6JDH's 30 meter mods for the 40A. These are more comprehensive than W0CH's mods and will be the ones we pursue on our builds. Stay tuned.

30 Meter Mods Per WB6JDH
(1) Install 8 MHz crystals
(2) T2 is wound as follows:
     Pri 2T
     Sec 17T
(3) T3 is wound as follows:
     Pri 18T
     Sec 4T
(4) C6 is 22 pF NPO
(5) C9-C13 are 470 monos or 470 C0G or 470 NP0 if they will fit
(6) L4 is 10 uH
(7) C14 is 47 pF NP0
(8) U2 same except X5 = 8 Mhz
    Pin 6 = 0.80 Vpp
(9) AGC Mute Circuit
     R4 is 4.7 MOhm
     R8 can be jumpered
(10) U4 Measurements:
      Pin 4 = 0.15 Vpp
      Pin 6 = 0.30 Vpp
(11) X6 is 8 MHz crystal
(12) L5 is 15 uH
(13) C35 is around 151 pF (see notes below)
(13) C38 is 68 pF NP0
(14) L6 is 24T
(15) Q5 Measurements
     Source = 1.0 Vpp
(16) T1 is wound as follows:
     Pri 13T
     Sec 3T
(17) R12 is 18-22 Ohms
(18) Q7 Measurements:
     Base 2.5 Vpp
(19) RFC1 = 15 uH
(20) L9 is 62T
(21) C52 and C53 are 1500 Poly
(22) Q8 Measurements:
     Source = 3.4 Vpp
     R23 on C7 side = 0.8 Vpp
     Rxvfo label = 0.8 Vpp
Regarding the oscillator circuit for U4, Dick was concerned because the drive to the base of Q7, the final transistor, was too low at 2.5 Vpp. At first, he thought it might be due to the crystal activity of X6 hanging off of pin 6. However, fishing through his stack of 8 MHz crystals and finding a substitution with more poop did not alter the drive that much.

Instead he proposed dropping the value of C35 hanging off of U4 pin 7 with something a little less than the 270 pF original. Dick tried a 150 pF NPO cap and reports that the power output for his 30m version was raised to just a shade under two watts. Recommend you try a temporary insertion until an optimum value is found. But be careful, however, as too low a value will swamp U4's oscillator.

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