26-10-2024, 08:56 AM
Another update.
Currently I am progressing with the attenuator I am making for my tinySA Ultra. It's to be with individually switched in units of minus 10, 20 and 30dB giving a range from 0 to 60dB. 50ohm. I have constructed the individual units, now I have worked out the needed resistor combinations for the calculated values along with increasing the power handling as much as sensible with the components I have. I have a plastic case for it but will use some of the tinplate I have for a degree of internal screening. Initial testing of circuitry proved that the calculations appear correct.
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Recently I have been working toward a few ideas on a superhet receiver, to include a valve push pull amplifier, for additional audio use. As is often with my ideas it's something which I may play around with more than actually use but it's something which has long been on my mind. With that, I am making use of a radio cabinet which I was given. This is rather small so I worked out that it would be tricky to get power sorted as well as everything else. consequently I have produced a stand alone power unit for this task.
This unit utilised a case which I had previously ued for a higher voltage power unit I made some years ago but since seldom used as I don't do much with higher voltages anymore. This unit had holes cut in the case and a fitted fan. I worked with and around these, hence the fan is still fitted and I use some of the original sockets as they are still useful.
The circuitry consits of a 50-0-50V transformer providing 60V at 70mA and 125V at 140mA via transistor regulators, these currents being more limited by transistor cooling and accepted ripple than anything else. They are higher than required though so adequate.
There is a 12V transformer providing -12V regulated for negative bias. It can be adjusted slightly upward but may well be increased with a higher voltage transformer at some point as 12V is a bit limiting.
Valve heaters are catered for by a switch mode module set to 6.3V output. This is fed via a 12V DC power input, via a 12V 9.5A computer power module I have. My requirements were for around 2.5 to 3A which this will supply. A further takeoff is made from the 6.3V to an IC regulator which provides a 1.25V output for rod pentodes that I use.
In my opinion this unit is a bit messy as, beside using a previously used case, I did have some trouble juggling things about to get the outputs I needed. Particularly the higher current at 6.3V. It's probably general but I have found it harder to get a large current output from a supply than any higher voltage, except perhaps when I was going well up into the hundreds and a just less than 1kV supply I once experimented with. This was still a current issue though as I was using a 12V supply to power an invertor switching two transformers in parallel and the startup surge was shutting down the 12V supply. Still that's in the past. I suppose the untidy part is that this unit has both mains and 12V inputs.
That said, it was meant to be portable, at least around the house, and has tested Ok. I have used it a little in my initial tests on my amplifier circuitry and it worked without issue.
The pictures shown should be fairly self explanitory. The circuitry is pretty standard stuff, the transisitor regulators being darlington series regulators with zener voltage setting. The 1.25 and -12V outputs are set by IC regulators. The 6.3V is set on the switch mode module.
Tracy
Currently I am progressing with the attenuator I am making for my tinySA Ultra. It's to be with individually switched in units of minus 10, 20 and 30dB giving a range from 0 to 60dB. 50ohm. I have constructed the individual units, now I have worked out the needed resistor combinations for the calculated values along with increasing the power handling as much as sensible with the components I have. I have a plastic case for it but will use some of the tinplate I have for a degree of internal screening. Initial testing of circuitry proved that the calculations appear correct.
-----------------------------------------------------------------------
Recently I have been working toward a few ideas on a superhet receiver, to include a valve push pull amplifier, for additional audio use. As is often with my ideas it's something which I may play around with more than actually use but it's something which has long been on my mind. With that, I am making use of a radio cabinet which I was given. This is rather small so I worked out that it would be tricky to get power sorted as well as everything else. consequently I have produced a stand alone power unit for this task.
This unit utilised a case which I had previously ued for a higher voltage power unit I made some years ago but since seldom used as I don't do much with higher voltages anymore. This unit had holes cut in the case and a fitted fan. I worked with and around these, hence the fan is still fitted and I use some of the original sockets as they are still useful.
The circuitry consits of a 50-0-50V transformer providing 60V at 70mA and 125V at 140mA via transistor regulators, these currents being more limited by transistor cooling and accepted ripple than anything else. They are higher than required though so adequate.
There is a 12V transformer providing -12V regulated for negative bias. It can be adjusted slightly upward but may well be increased with a higher voltage transformer at some point as 12V is a bit limiting.
Valve heaters are catered for by a switch mode module set to 6.3V output. This is fed via a 12V DC power input, via a 12V 9.5A computer power module I have. My requirements were for around 2.5 to 3A which this will supply. A further takeoff is made from the 6.3V to an IC regulator which provides a 1.25V output for rod pentodes that I use.
In my opinion this unit is a bit messy as, beside using a previously used case, I did have some trouble juggling things about to get the outputs I needed. Particularly the higher current at 6.3V. It's probably general but I have found it harder to get a large current output from a supply than any higher voltage, except perhaps when I was going well up into the hundreds and a just less than 1kV supply I once experimented with. This was still a current issue though as I was using a 12V supply to power an invertor switching two transformers in parallel and the startup surge was shutting down the 12V supply. Still that's in the past. I suppose the untidy part is that this unit has both mains and 12V inputs.
That said, it was meant to be portable, at least around the house, and has tested Ok. I have used it a little in my initial tests on my amplifier circuitry and it worked without issue.
The pictures shown should be fairly self explanitory. The circuitry is pretty standard stuff, the transisitor regulators being darlington series regulators with zener voltage setting. The 1.25 and -12V outputs are set by IC regulators. The 6.3V is set on the switch mode module.
Tracy
