[TMC] Sideband Exciters

[John Vendely]

Ya got me curious about the purpose of KIT-248, a substantial 
modification of the exciter which includes, among other things, 
replacement of transformers and installation of a special network 
(NW-127).  Yer right, it definitely affects much more than the RF output 
power; there also appear to be mods to the 17 kc and 287 kc oscillators, 
and the balanced mixers in the upconverters.  A nearly complete 
realignment of the exciter is required.

Two things about the documentation for TMC's modification kits which 
always bothered me are evident here.  They often do not state the 
purpose of the mod or provide a schematic showing the overall changes.  
One would expect a schematic addendum for insertion in the manual after 
updates.  They give good, detailed installation instructions, but it 
often requires considerable scrutiny and reverse-engineering to 
determine the purpose.  My guess is that KIT-248 fixed a number of 
extant problems, including reducing spurious emission levels.

There doesn't seem to be a SBE-2A manual.  So, did TMC ever produced an 
SBE-2A, or did it exist only as the result of this modification to 
existing exciters in the field?  The reason I suspect this is that, by 
1966, TMC offered the SBE-3 (and SBG) with 3 kc BW sideband filters, a 
superior design which would have obsoleted the SBE-2...

73,

John K9WT

On 8/28/2021 9:50 AM, John Poulton wrote:
> If you want the gritty details of converting and SBE-2 to a -2A, see:
>
> https://tmchistory.org/tmc_drawings/drawings_db/s/s-docs_900-999/s_952.pdf
>
> which details the procedure.  Irritatingly it doesn't say *why* you might
> want to make these changes!  The parts list runs for 2 pages, and includes
> mods to wafer switch S106, so I think it's more than just power output..
>
> 73, John K4OZY
>
>
> On Sat, Aug 28, 2021 at 3:38 AM Robert Downs via TMC <tmc at mailman.qth.net>
> wrote:
>
>> I have many of the TMC manuals.  There are actually two possible reasons
>> for the "A" suffix on the SBE-2A.  The first was the addition of an ALDC
>> (Automatic Load Drive Control) mod for the SBE-2.  But the slightly later
>> one and more likely the reason for the "-A" was a kit of parts to optimize
>> operation at about 250 mW PEP output (the SBE-2 was rated at up to 1 W
>> output).  The kit consisted mostly of resistors of slightly different
>> values from those in a stock SBE-2.
>>
>> Robert Downs
>>
>>
>> -----Partial Original Message-----
>>
>>>> ________________________________
>>>> From: BERMAN <triodes at optonline.net>
>>>> Sent: Friday, August 27, 2021 2:52 PM
>>>> To: Meir Ben-Dror WF2U; Nick England
>>>> Cc: George W1LSB via TMC
>>>> Subject: Re: [TMC] Sideband Exciters
>>>>
>>>> Meir, thanks for the input on the SBE-series of exciters.
>>>>
>>>> I have a model SBE-2A (not SBE-2) exciter integrated within my
>> GPT-750. Do you (or anyone else here) know how the SBE-2A differs from the
>> SBE-2 or the later SBE-3?
>>>> I ask this as I was unaware that the SBE-3 and later variants were
>> less of "a pain in the neck" when compared to those units that were of the
>> earlier pre-SBE-3 design.
>>>> 73,
>>>>
>>>> Bruce, W2XR
>>>>
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