[Heathkit] SB-104A SSB drive problems

[Bob Macklin]

If you get full output with a signal generator the problem in not in the 
transmitter. It is either the mike or the way you are using it.

Are you using a monitor scope on the RF output or just reading the meter?

Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"

----- Original Message ----- 
From: "William Houghton" <rdrbill at pacbell.net>
To: <heathkit at mailman.qth.net>
Sent: Wednesday, November 03, 2010 12:16 AM
Subject: [Heathkit] SB-104A SSB drive problems


> Hi fellow Heathkit fans,
>
> I'm having a problem with an SB-104A that I'm trying to get up an running. 
> It
> seems that I can't drive to full output with any of my mics. Heathkit 
> specs the
> mic requirements at -45dB to -55dB (aprox 1.6mV to 5.6mV of drive). My 
> D-104
> provides about 20mV at normal voice volume. It should be able to drive 
> this rig
> easily.
>
> In CW mode, I have full output.
>
> Per the Heathkit technician notes on the web, I did drive the mic input 
> with a
> 1KHz signal at 150mV and did get the proper amplitude at the input and 
> output
> stages of the TX audio section. With a 150mV input signal the rig does 
> drive to
> full output. This seems to vindicate the TX audio stage (LM3900 and the 
> emitter
> follower transistor).
>
>
> I'm wondering if the balanced modulator has an issue. I have to admit, 
> that I
> don't fully understand how the modulator circuit works - I'll have to do 
> some
> studying :).
>
> Anyone ever had this type of problem before? I'm open to all suggestions.
>
> Thanks & 73,
>
> WA6NEQ (Bill)
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