I would not like to build a stabilized power supply, as that would be
quite a huge machine. Anyway I shall give a look to the diagram and see
whether there would be any simple way to feed just the oscillator tube
with a separate stabilized HV.

With regard to voice peaks, using big output capacitor should help.

I am more worried about CW because, even with a big output capacitor,
voltage will tend to decrease along the duration of a dash or a dot, and
this may cause chirp.

Going back to my original question, the first test I shall do is to feed
the filaments with a transformer, while keeping the dynamotor for the HV.
I want to be sure that powering filaments on AC (instead of DC) does not
cause an unacceptable hum on the audio.

By the way, I have been looking for a spare VT-25 (10Y) tube, but I could
not find one for less than $70. Apparently that tube is one of those that
had the disgrace to fall into the esoteric hi-fi aficionados circuit, who
are prepared to pay almost any price for the promise of a "warmer" sound.

73

Tony I0JX

Oh, Wow! Been a long time ago, but more than 50 years ago, three or four of
us,
(W7KGV, W7MGG, W7LAN and I, W7LTQ) were tinkering with BC-375's,
the 28 volt version of the BC-191.
The power supply regulation with the dynamotor seemed to be almost
entirely dependant on the DC input to the dynamotor. If one had new, hunky
batteries, with very short (two feet max) very heavy (gauge # 000, maybe)
leads and
a constantly running battery charger, the CW wasn't too bad. HOWEVER,
my batteries were old and weak, dynamotor input leads were doubled up
#10 house wires, and one almost had to copy the transmitted CW with one
hand on the tuning knob. (Yeow, ditty, yeow yeow)
A long dash slowed the dynamotor to maybe half speed, and the glowing
filaments went from white hot to more like cherry red.
Later, an AC power supply was cooked up, using conventional circuitry
of the day, pair of 816 mercury vapors, "swinging" choke input to pi section
filter, maybe 4 microfarad filter condensers, a "smoothing" choke and a
50,000 ohm
bleeder resistor. The '375's filaments were lit with 10 volt AC
(transformer), and a
dropping resistor for the speech amplifier (10Y)'s filament. Seems to me,
there was
something about which side of the 10Y's filament was ground that made a
difference
in the hum level.
With that sucker, delivering a stiff 1200 or 1300 volts on the MOPA's
final VT-4C,
it's plates would turn a soft red blush on long dashes..... and would work
anyone
you could hear!
Old Chief Lynn

With that sucker, delivering a stiff 1200 or 1300 volts on the MOPA's
final VT-4C,
it's plates would turn a soft red blush on long dashes..... and would work
anyone
you could hear!
Old Chief Lynn

Thanks for info,

I have no problem at all with the dynamotor, as I power it using a stabilized
computer mainframe power supply that easily delivers 100A with no voltage drop
at all.

But the dynamotor is too noisy; moreoverr it becomes fairly hot if kept running
for long periods.

Yes, the solution of using a resonant.choke power supply is probably the most
appropriate for obtaining a stable HV, but it is not easy to find a suitable
choke. Will see what I can do.

73

Tony I0JX

I know it seems like cheating.... but... consider a zener and TIP50
darlington.
--scott


Yes, using a series regulator is certainly a possibility.

With a current of up to 350 mA (average) and a voltage drop across the
regulator that cannot reasonably be lower than 250V, the power dissipated in the
regulator would be around 90W, which is not enormous but not negligible either.

However in my case I plan to obtain 1000VDC using a voltage doubler. So I could
use two separate series regulators on each of the two 500VDC arms of the supply.
This would probably make the design simpler.

73

Tony I0JX

Antonio Vernucci wrote:
With that sucker, delivering a stiff 1200 or 1300 volts on the
MOPA's final VT-4C,
it's plates would turn a soft red blush on long dashes..... and would
work anyone
you could hear!
Old Chief Lynn

Thanks for info,

I have no problem at all with the dynamotor, as I power it using a
stabilized computer mainframe power supply that easily delivers 100A
with no voltage drop at all.

But the dynamotor is too noisy; moreoverr it becomes fairly hot if kept
running for long periods.

Yes, the solution of using a resonant.choke power supply is probably the
most appropriate for obtaining a stable HV, but it is not easy to find a
suitable choke. Will see what I can do.

73

Tony I0JX

Tony, I wrote up a mod I came up with for Electric Radio, last year.
I'll send you the diagram for it if you'd like. Essentially, it moves
the filament 24v from the output side of the power contactor (inside the
dynamotor relay box, on top) and moves it to the input side. That way,
the filaments light up and gets things warmed up whenever power is
applied. When you want to xmit, just hit the power switch. When you're
done turn the switch off. My next trick will be to route PTT to an
external relay which will both key the transmitter and turn on the
dynamotor (paralleling the front panel power switch). When PTT is
released, the dynamotor stops. That way, no duty cycle problems arise.
Note also that in the manual, it says that the duty cycle of the
dynamotor is about 30 minutes, and that is at altitude. At room temp, I
figure one has about 15 minutes before things bad happen. The book also
says for ground maintenance activity, remove the dynamotor end bells for
cooling. Unlike the ART-13 and similar heavy-duty dynamotors, there is
no throughput cooling blower on the PE-73 or BD-77.

Regards Jeep/K3HVG



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Tony, I wrote up a mod I came up with for Electric Radio, last year. I'll
send you the diagram for it if you'd like. Essentially, it moves the filament
24v from the output side of the power contactor (inside the dynamotor relay
box, on top) and moves it to the input side. That way, the filaments light up
and gets things warmed up whenever power is applied. When you want to xmit,
just hit the power switch. When you're done turn the switch off. My next
trick will be to route PTT to an external relay which will both key the
transmitter and turn on the dynamotor (paralleling the front panel power
switch). When PTT is released, the dynamotor stops. That way, no duty cycle
problems arise. Note also that in the manual, it says that the duty cycle of
the dynamotor is about 30 minutes, and that is at altitude. At room temp, I
figure one has about 15 minutes before things bad happen. The book also says
for ground maintenance activity, remove the dynamotor end bells for cooling.
Unlike the ART-13 and similar heavy-duty dynamotors, there is no throughput
cooling blower on the PE-73 or BD-77.

Thanks Jeep,

I have already separated the 12VDC filament supply from the dynamotor 12VDC
supply.

However I cannot use the dynamotor in the "PTT mode" because my dynamotor power
supply is unable to start the dynamotor quickly. Though being a 100A stabilized
power supply, its overcurrent protection trips until the dynamotor has not
reached a certain speed. So, I must run a start-up procedure which takes time
and is incompatible with operating the dynamotor in PTT mode. Perhaps putting a
big car battery in parallel to the supply would solve the problem.

In any case I prefer not to use that noisy dynamotor and I am therefore
currently building an AC supply.

73

Tony I0JX