[TMC] SBT-1KV lives!

[Gary Schafer]

When tuning any tetrode (or pentode) you should watch the screen current
meter rather than the plate current. The screen current is much more
sensitive than the plate. Tune the plate tuning for maximum output and at
the same time the screen current will peak. Increasing loading will bring
the screen current down. Then repeak it again with the plate tuning.

If you are running too much screen current you have either too light loading
or too much drive. That is if your screen voltage is set properly.

73
Gary  K4FMX

> -----Original Message-----
> From: tmc-bounces at mailman.qth.net [mailto:tmc-bounces at mailman.qth.net] On
> Behalf Of Duncan M. Brown
> Sent: Wednesday, February 04, 2009 11:15 AM
> To: Roy Morgan
> Cc: tmc at mailman.qth.net
> Subject: Re: [TMC] SBT-1KV lives!
> 
> 
> > >  Got
> > > 800 watts out on 75 M into dummy load.
> >
> > John asked me what the thing should put out.  I guessed 1500 watts or
> > more key down, full output.  Of course with SBE drive on AM, you'd set
> > one quarter of peak (or desired peak) power.
> >
> 
> The spec for the SBT-1K (TB 1001A) says "1000 watts PEP, SSB, CW, FSK".
> This implies 1KW PEP AM, which would be 250 w carrier.
> 
> >
> > > (Didn't try higher power because the
> > > screen current meter was about to peg. Need to play with it a little
> > > more.)
> >
> > Is final tuning done by peaking the screen current?
> 
> Final tuning is done with the standard peak & dip of the output stage
> plate
> current (and/or for maximum RF output). But they warn to watch the screen
> current and don't let it go above 100ma (meter max). From what I've read
> typical SG current seems to be in the order of 30-50 ma.  In the TMC-list
> archives, I read Larry (W0OGH)'s comments from a few years ago saying that
> it was hard to keep the screen current down and it seemed to change a lot
> with the output loading.  This was fjust the initial test to see that the
> unit put out power, still some tweaking to do.
> 
> >
> > > How do you key your TMC transmitters for PTT service?
> >
> > Seems to me  that there's a connection from the SBE to the GPT-750
> > that turns on the HV and maybe driver stages on PTT.  The 750's master
> > oscillator does run all the time, though.
> >
> >
> > > ....  Am I missing a jumper
> > > somewhere that allows the mic to also key the TX voltages?
> >
> > I would guess you are missing one.  Who knows where it is though.
> > >
> > >
> 
> I have three different manuals that I am trying to gleen all the important
> information out of, so it may take awhile to figure it all out.  The other
> problem is that, since the SBT-1KV is at the Museum, I can only work on it
> one day a week, which slows things down a bit.
> 
> > I hope to tune you in on the AM Qso Party.
> 
>  The SBT-KV will probably be on 20M, so I don't think we will be able to
> work you there, but we will have the James Millen station on 75M, with a
> full-wave loop antenna.  Probably have a Viking Valient and HQ-180 on 40M.
> 
> 
> >
> > Great going!
> 
> Thanks,
> 
> Duncan, K2OEQ
> 
> >
> > Roy
> >
> > Roy Morgan
> > k1lky at earthlink.net
> > 529 Cobb St.
> > Groton NY, 13073
> >
> 
> 
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