[Heathkit] SB-104A SSB drive problems

[rbethman]

Bill,

Knowing that you get "full output in CW", I would ask if you have a 
"peak" reading watt meter you can put in-line to a dummy load?

You may NOT be seeing the actual power level out EVEN with a monitor 
scope.  Since a monitor scope spreads out the total power over a "range" 
of frequencies, it would require a peak reading watt meter to determine 
*IF* you are or are not "really" getting the full output on "other" than 
the CW mode.

Bob - N0DGN

On 11/3/2010 12:43 PM, William Houghton wrote:
> Bob, Heinz,
>
> First, thanks for your comments.
>
> I am using a Heathkit monitor scope (an I/O-10 that I also use with my Drake
> TR-4C and other rigs). The RF output of the rig goes to the scope, the other
> scope connector to the dummy load (internally the scope connectors are just feed
> thru's).
>
> Let's repeat the info. The Heathkit spec is for a mic with an output level of
> -45dB to -55dB. This info is from the SB-104A specs in the Operations Manual. In
> those days it was dBV (i.e- referenced to 1V). This translates to a signal level
> of between 1.6mV to about 5.6mV. From two sources on the web, I have seen notes
> that are said to be from Heathkit service techs. In these notes, they checkout
> the TX audio stages by applying a 1KHz, 150mVp-p signal into the mic input and
> then measure the outputs and inputs at the various stages. Compared to the mic
> requirements, this is about 30 to 100 times larger than what should be
> needed.The TX audio stage of my rig seems to match closely the Heathkit service
> tech info. For example, on the emitter of the emitter follower buffer
> transistor, the techs says you should see 0.63Vp-p. I see slighty over 600mVp-p.
> Under these conditions my rig will produce full output for the power mode in
> use. This tends to make me think that the TX audio stage is okay. Do you agree
> with this? Or is there a significant difference in circuit performace with 5mV
> signals compared to 150mV signals? I would think that both would be considered
> "small signal gain".
>
>
> The next stage this feeds is the balanced modulator. From the schematic it seems
> that a signal from the mode switch (about +11V) is used to 'unbalance' the
> modulator allowing unmodulated RF to go through the modulator's transformer. In
> CW mode, the rig produces full output.
>
> Any input is appreciated.
>
> thanks,
>
> Bill