[Milsurplus] TBW Transmitter power-ON - filament wiring

[Richard Brunner]

OK Gang:
Actual measurements on 800 cycles; panel voltmeter set on 10 volts,
T-202 terminals 9 to 11, 16.04 volts measured with a true rms meter.

The 837 heater is 12.6 volts at 0.7 amps, so the voltage drop through
R-312 (4.5 Ohms) is 3.15 volts; 3.15 plus 12.6 is 15.75 volts, which is
good agreement.  There is fractional voltage drop through the wiring, so
the 837's are probably right on.  Gotta run now, but might measure the
837's later.

Richard, AA1P


On Thu, 2009-06-04 at 00:04 -0400, WA5CAB at cs.com wrote:
> Greg,
> 
> The rectifier-modulator originally had three transformers in it.  On for 
> high B+, one for low B+ and one for filament.  The filament transformer had a 
> 105 VAC primary and a rheostat in series with it.  You used the rheostat to 
> set the filament volt meter to 10.0.  According to the TBW, TBW-1 and the 
> TBW-5 manuals, the winding for the 837's in the HF transmitter was 9.3 VAC 
> each side of center-tap, and rated at 1.4 amps.  The 1.4 makes sense as the 837 
> filament current is 0.7 amps at 12.6 volts.  There is a 4.5 ohm resistor in 
> series with the filament of the IPA but it would only drop the applied 
> filament voltage to about 15.2 volts.  Actually, it would probably be a little 
> higher than that as the filament current will decrease a little as you raise 
> the voltage.  There is no voltage and resistance chart in any of the manuals 
> but my guess is that the 9.3 is wrong.  The same transformer shows the 2.5 
> volt winding for the 843 modulator as rated at 205 amps.  I believe that the 
> 205 should be 2.5.  The 837 VFO has a bifilar RF choke in its filament 
> circuit but its resistance is not given.  From other information it would 
> probably be possible to calculate it within say +/- 20% but I didn't do it.  
> 
> Perhaps someone with a working TBW (I don't mean just the HF transmitter) 
> could measure the RMS voltage on T-202 between terminals 9 and 11.  
> Alternately, you could measure the resistance of the two choke windings and add them. 
>  If close to 4.5 ohms, then I would guess the filament winding output was 
> around 16 volts.  If significantly lower than 4.5, then I would guess it was 
> a 12.6 volt winding and for some reason they ran reduced filament voltage on 
> the IPA.
> 
> In a message dated 6/3/2009 7:46:33 PM Central Daylight Time, 
> bluebirdtele at embarqmail.com writes: 
> > Thanks to all for your input.
> > Some folks say don't modify it if it's in NOS condition.  Others say do 
> > what 
> > you need to do to get it on the air.
> > I think I will split the difference and try to fire it up without cutting 
> > or 
> > soldering stuff in.
> > A home brew supply is  nearly finished and out putting 1.6 kvdc and 500 
> > vdc 
> > unloaded.  Also, 10 vac @ 5 amps and 12 vac is available onboard.
> > All I have to work with is a smallish system schematic and I looked at the 
> > 
> > filament wiring for the HF unit.  The two 836's are wired together at the 
> > filaments and what looks like a resistor array for both.  Since the 836 
> > lists as a 12 v tube, I wonder what uncle Sam  used for filamant power.  
> > Any 
> > ideas?
> > Thanks
> > Greg
> > WA7LYO
> > Kinston NC 
> 
> Robert & Susan Downs - Houston
> wa5cab dot com (Web Store)
> MVPA 9480
> ______________________________________________________________
> 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