still:SB-104A problem

[Kees & Sandy]

Right .... in that it sounds like the TX/IF board "C". You can
check these points from the bottom without an extender:

*  first, this is a kit built by someone. I don't remember if you
   said it worked before or not. If not, maybe some components
   are switched/wrong/have solder bridges in the 15m and 20m
   sections. Check the schematic. This is the "first rule of kits"
   ....it didn't necessarily work before, regardless of what the
   seller told you unless YOU saw it working.

* check the switching diodes. The switching diodes are normal
   silicon types and are not that critical ....use a common 1N914
   if you need one. Do not use 1N914s for any of the mixers or
   any signal diodes.

* make sure the band select for 15m (pin 19) and 20m (pin 20)
  have the same levels as 40m (pin 21) when selected.

* The injection level (pin 10) should be around .4-.5vRF for
  20m and .3-.4vRF for 15m. As a reference 40 m is .5-.6vRF

* The RF OUT (pin 24) should be about .6vRF for 15m, .7vRF
  for 20m and .8vRF for 40m

* The Driver and PA boards are broadband and not frequency
   selective. The Filter/ALC board IS frequency selective but you
   already bypassed that.

* The LOW POWER output from the Driver Board (NOT the PA
   Amplifier) should be about 9.5vRF for 15m, 20m, and 40m.
   The PA Amplifier RF voltages are on the order of 100vRF and
   you have to be really careful making measurements.

The SB-104(A) is a great little transceiver with lots of history and
works well today on the air as it did years ago. So do the Heathkit
tube rigs. So do old tube type Collins KWM-2s. Fun stuff to use
and maybe improve on a little here and there.

73s Kees K5BCQ

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