For anyone interested the answer seems to be 18V. The third transistor from
the back has maximum bias voltage of 0.807 at 19V and it drops to 0.804 if
increased to 20V. But when I switch the "enable" line the bias currents
seem to "run away" a bit. What do I mean? Basically at 18V all bias
currents stabilise at 0.8A. At 19V it keeps on increasing to 900A and over
1A. I didn't carry on not wanting to blow it up.
So I think 18V will be one voltage I'll run it at. It would be nice to get
more power and give the finals 24V. But running one voltage instead of two
is better of course.
73,
Lukasz
So that is the target voltage. Now the question is... Can it work at 24V?
On Sat, 12 Apr 2025, 09:11 Lukasz, <sp4it.mail@gmail.com> wrote:
> Great. Thank you for the reply. Good tip about the logic Vcc.
>
> 73, Lukasz I 8
>
> On Fri, 11 Apr 2025, 17:35 Steve Thompson via Amps, <amps@contesting.com>
> wrote:
>
>> It's almost certainly 24/28V for the main power to the driver and
>> output. I used to work for a company which supplied transistors for
>> other Ericsson base station equipment and everything was 28V (same with
>> Nokia NMT450 gear).
>>
>> To check what the 'logic Vcc' supply input should be, leave power to the
>> driver/output disconnected and use a bench supply to gradually increase
>> the voltage while monitoring the bias voltage going to the input tabs of
>> the driver and output stages. At some point the voltages should
>> stabilise which will be the 'logic Vcc' that you need - probably around
>> either 12V or 24V.
>>
>> Steve G8GSQ
>>
>> On 11/04/2025 08:27, Lukasz wrote:
>> > I've recently got my hands on some ancient mobile phone base station
>> > amplifiers which I've managed to retune to 435Mhz +- 5MHz but I need
>> some
>> > help with choosing the voltage to run them at.
>> >
>> > Does anyone in this group have any knowledge of such old cellular
>> hardware?
>> > Specifically power and logic voltages used?
>> >
>> > These amplifiers are only 50W, but they are very nice if one wants to
>> bump
>> > a -10dBm SDR output to usable power (got 12W from -5dBm at 12V) to use
>> one
>> > of the high frequency SDRs like Lime (or maybe Pluto, I use Limesdr).
>> >
>> > The amplifiers use bipolar transistors in a 5 stage design. First 2
>> stages
>> > are in a little metal can and they are two of BCP54 transistors (45V
>> max)
>> > with 3 unable core filter cans between them. Also same transistors are
>> used
>> > to switch power to other RF stages.
>> >
>> > Then there is SGS Thomson 1310 transistor, 1391 and finally 1393. As
>> far as
>> > I can tell with my nanovna probing first 4 stages are very wideband
>> (pretty
>> > much flat between 300Mhz and 600mhz) and the filter cans are used to
>> narrow
>> > the input down.
>> >
>> > The final transistor uses a tuned input but it's output again is very
>> > wideband (3dB bandwidth is again over 300mhz). So all i had to tune were
>> > the input cans and anf the input circuit of the final.
>> >
>> > The thing is powered by an 11 pin plug. First two pins appear to go
>> > directly to the final and one prior transistor power supply. Then we
>> have
>> > something I called "logic Vcc" it is power for a quad op amp circuit
>> that
>> > sets the bias, the 1391 and other transistors thar switch power on/off.
>> > This is the voltage I'm mostly trying to find. It works from as low as
>> 5V,
>> > but it produces a lot more power at 12V.
>> >
>> > Then there are tewo enable pins that have to be over 3V for bias and
>> power
>> > to be supplied.
>> >
>> > I haven't discovered the purpose of other pins, but I suspect they
>> might be
>> > status outputs.
>> >
>> > I know all transistors can survive 40V. I believe the final may have
>> run on
>> > 24V.
>> >
>> > But not sure about that logic supply that also powers 1310 transistor
>> and
>> > earlier stages. The opamp (3303) is fine with up to 36V (+-18V). But I
>> have
>> > no way of knowing how these bias circuits are set (there are smd pots).
>> >
>> > Can anyone suggest how to find the correct value for that voltage?
>> >
>> > 73, Lukasz
>> > _______________________________________________
>> > Amps mailing list
>> > Amps@contesting.com
>> > http://lists.contesting.com/mailman/listinfo/amps
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|