Thank you very much for all of the input. It was extremely helpful, yes the
power supply will be used on a 200 watts ATV repeater amplifier and will be
running 24/7. I have been taking a look at the ARRL handbook and figure that
might be a good starting point but I am going to re-read all of the
information that all of you provided and come up with a suitable power
supply. Once again that you everyone for you suggestions and information.

73's

Craig
"G.Beat" wrote in message
newshp1d.297505$8_6.74360@attbi_s04...
"Paul Keinanen" wrote in message
...
On Mon, 13 Sep 2004 12:36:04 GMT, "G.Beat"
wrote:

Paul and Eric and provided a good background on how to adopt the ARRL
design.
You can substitute the 2N3771 transistor for the common 2N3055 pass
transistor (this is what Astron has done on many of their latest
models).

This suggestion makes sense for low voltage (5-12 V) high current
power supplies, since the worst case current gain (15) has been
specified for Ic=15 A and in general, the typical current gains are
better at very large currents than with 2N3055. Also the Vbe and
Vce(sat) voltages are lower at similar collector currents, thus, the
capacitor voltage can be slightly lower.

[snip]

Please note that the maximum Vce for 2N3771 is only 40 V and since the
capacitor voltage can exceed 40 V and in case of a short circuit, the
emitter is close to 0 V, the Vce could be exceeded. At least use the
2N3772 for the 24 V supply, since the maximum Vce is 60 V. The 2N3055
is also specified for Vce=60 V.

Paul OH3LWR

Yes, I also have the 2N3772 in my parts replacement bin - and have used as
replacements for shorted 2N3055 pass transistors.

w9gb

On Mon, 13 Sep 2004 22:50:08 +0200, J M Noeding
wrote:

I suppose it is to be used for a linear amplifier,

Apparently this was needed for ATV, however, I have no idea if it was
for AM/VSB-ATV or FM-ATV.

and then it is a not a good idea to use stabilized voltage.

This is certainly true for tube amplifiers which can tolerate high
standby voltages.

However, especially with bipolar RF transistors, if you first run them
at a lower voltage, high current and high dissipation and thus finally
with a high junction temperature and then reduce the loading, the
power supply voltage is increasing to the standby value, you are going
to have secondary breakdown problems.

When operating with an unregulated power supply, you must make sure
that during idle condition and maximum mains voltage, the storage
capacitor voltage is always less than the maximum allowed Vce for the
RF transistors. However, when loading the amplifier, the power supply
voltage drops 10-30 %, thus the RF output would drop even to one half
of what would otherwise be available from these RF transistors,
assuming adequate heatsinks.

It makes perfectly sense to use cheap series pass regulator
transistors in order to get the maximum power out of the expensive RF
transistors by running them all the time close to the maximum allowed
voltage.

Even if you accept the hum problems associated with unregulated
supplies, at least use some simple series pass regulator to limit the
standby voltage to the maximum allowed for the RF transistors. When
the capacitor voltage is below this maximum, simply put this regulator
into saturation, with less than 1 V drop, thus the amplifier Vcc
follows quite closely the capacitor voltage during discharge. The
dissipation in these series pass transistors would be quite low (low
current at high voltage difference, only the saturation voltage at
high current).

It might have been needed
for 14V, although Atlas 210-X was operated without - with a varying
voltage between 11-16V, but is not the same problem for 24V.
With maximum voltage of +32V the output may drop down towards 24V, and
no problem at all - apart from setting a limit for the power input

Only problem that you must use 32 V RF transistors (64 V for collector
modulated AM). With a regulated 24 V supply, you could use 24 V (48 V
AM) RF-transistors and get the same RF output assuming identical power
dissipation and current handling figures. The price for higher voltage
transistors is usually higher.

With AM/VSB-ATV this will cause truncation of the sync pulses and
possibly hum bars in the received signal (since the receiver a.g.c is
derived only from the "constant" amplitude synch pulses :-). On FM-ATV
there could be two noise bands across the screen.

Paul OH3LWR