[Milsurplus] 'splain me this 6L6 transmitter circuit

[Al Klase]

My SWAG (silly wild-assed guess) is that it makes the 6L6 a better 
doubler on the high band.  I don't recall seeing a lot of WWII era 
crystals higher than about 9 MHz.  Also, don't ask me which switch 
position is which.

Al

On 5/17/2013 3:15 PM, mac wrote:
> Some kind of a key-click filter maybe?
>
> Dennis D.  W7QHO
> Glendale, CA
>
> ******************
> On May 17, 2013, at 12:10 PM, Hue Miller wrote:
>
>> Maybe I have asked this question already?
>> Sorry, I tend to forget, but I don't recall any definite answer.
>>
>> Imagine a basic 6J5 + 6L6 MOPA. Xtal controlled Pierce osc.
>> untuned plate, driving 6L6.  B+ under load, 340 volt. The
>> frequency range is 2 bands, 4 - 7.5 and 7.5 - 14 Mc/s. Okay?
>> However, in the cathode of the 6L6, is a "transmitter bandswitch".  
>> All it does is, one band, cathode goes straight
>> to keying relay. I think this is the low band. Schematic does
>> not say what band the switch positions are, but I am guessing
>> low band, because the rceceiver section is set, in the drawing,
>> to the matching low band.
>> So, in the high band, the 6L6 cathode is switched to go thru
>> a parallel 2.5 mH choke and 240 pF capacitor.
>> Okay, consider the choke infinite for RF.
>> So why is the 240 pF capacitor in the RF path?  Is this possibly
>> to provide RF degeneration?
>> NO word in the manual explaining this.
>> BTW, rig is US Navy "MBM" radio, apparently built by 
>> Jefferson-Travis, to be supplied to guerilla forces in occupied
>> Philippines 1945. It could either be powered by handcrank, or
>> by separate power supply from a built in 6 volt wetcell battery.
>> According to the book "You're No Good To Me Dead", at least one using 
>> team found the radio a total loser. I am
>> guessing that this was from the wet battery not for whatever reason 
>> not having a full charge, and maybe the
>> antenna tuning procedure being not clearly marked.
>> And, as the book describes, you would not want to walk
>> thru downtown Japanese occupied Manila lugging two
>> huge unique looking suitcases, one for the radio, one for
>> the power supply. In fact on one mission, the team sent
>> into Manila was spooked enough that they just threw
>> the suitcases into the bay. They said they felt they were
>> carrying a neon sign that flashed, "I am a spy".
>> Your take on this circuit?
>>
>> The receiver is also a little strange. Right out of the mixer
>> is a single tuned circuit. Why not a standard IF can here,
>> or did they NOT want good selectivity?
>> The radio looks odd, too, in a BC- 312 random controls
>> location kind of way. I have long felt that Jeff-Trav always
>> tended to produce radios that looked kind of odd.
>> tnx  -  Hue Miller 
>> ______________________________________________________________
>> Milsurplus mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Milsurplus at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/