[Heathkit] SB-104A SSB drive problems

[Bob Macklin]

I'm sorry but if it works properly with a signal generator the fault is not 
in the transmitter.

We don't know how he is making his judgment that he is not getting full 
output. The meter will not tell him!

He needs to look at the RF output with a scope!

Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"
----- Original Message ----- 
From: "Heinz Breuer" <hbreuer at debitel.net>
To: "Bob Macklin" <macklinbob at msn.com>
Cc: "William Houghton" <rdrbill at pacbell.net>; <heathkit at mailman.qth.net>
Sent: Wednesday, November 03, 2010 7:41 AM
Subject: Re: [Heathkit] SB-104A SSB drive problems


> No it is a fault in the TX section, probably the mic amp. He needs a 
> signal about 100 times stronger than specified. A LM3900 should still  be 
> available.
> Vy 73 Heinz DH2FA, KM5VT
>
> Von meinem iPhone gesendet
>
> Am 03.11.2010 um 14:53 schrieb Bob Macklin <macklinbob at msn.com>:
>
>> 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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>>
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>