[TenTec] QRP mod for TenTec Omni B?

[Carl Moreschi]

I had an Omni A series B and now that you say that I recall my radio 
would also go down to almost no watts also.

Carl Moreschi N4PY
58 Hogwood Rd
Louisburg, NC 27549
www.n4py.com

On 11/14/2014 2:49 PM, Neil Martinsen-Burrell wrote:
> As a follow-up on my message from earlier this week, I hooked my Omni B up
> to a dummy load and measured the power out using a DVM and a diode
> detector.  Besides verifying that the max power was around 104 watts on
> both 40m and 80m, I was able to turn the power down essentially as low as I
> wanted just by turning down the DRIVE knob.  I was able to get down
> reliably to around 3V peak (approx. 1 watt).  It did not take much turning
> of the knob to get down to sqrt(5)*10 = 22.4 volts (approx. 5 watts).
>
> I mistakenly trusted the manual which specified that the DRIVE knob will
> only turn the power down to 25 watts.  That does not appear to be the case
> on my Omni B.  It is possible that my radio is mis-adjusted or already
> modified in some way, but I think that is unlikely as the radio has been
> serviced at the factory a few times in its life already.
>
> I didn't hear any of the 80 meter foxes on my low dipole, but I was ready
> with just 5 watts to call them back!
>
> -Neil KD0UKC
>
> On Tue, Nov 11, 2014 at 4:05 PM, Neil Martinsen-Burrell<
> neilmartinsenburrell at gmail.com>  wrote:
>
>> With the upcoming QRP Fox Hunt season (one of my favorite weekly operating
>> opportunities) I am interested in the possibility of using my main station
>> rig at QRP power levels.  My QRP radio is an HB-1A with RIT that does NOT
>> remember the offset settings when RIT is switched off and then on.  This
>> means that it take a lot of fiddling to listen to a split pile-up to find
>> the station currently being worked.  I would prefer to use the Omni with
>> its separate offset knob and a RIT on/off switch so that I could easily
>> switch between the offset and non-offset frequencies.
>>
>> There are google mutterings from the late 1990s in this list's archives
>> about a mod that might change the range of the ALC knob from 0-20 instead
>> of 25-100 watts.  Does anyone know if such a mod exists as more than a
>> rumor?  On my previous Kenwood TS-520SE, there was an external ALC pin that
>> could be driven with a negative voltage to reduce output power.  Is there
>> something similarly simple for the Omni 546B?
>>
>> I can see from the schematic that R21 on the 80743 low level driver
>> controls the effect of the ALC control pot, but it seems like that isn't an
>> easy solution to getting down to QRP power levels, at least without some
>> fiddling to figure out what value would give the appropriate minimum and
>> maximum power levels.
>>
>> Thanks in advance for any help you can offer.
>>
>> -Neil KD0UKC
>>
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