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HIHI!
Ok, I understood the idea about the zeners and the transistors circuit.
Meanwhile, I was also thinking of a simple relay circuit, attached.
It works like this. When there is 12v in the line, the 24v relay cannot actuate and only the preamp is fed with 9v through the regulator.
Rx lowers...
Yes, I am talking about feeding the preamplifier with 12v. Then the voltage is increased for the rotations of the motor of course. As long as the motor does not need to be rotated, the voltage falls back to 12v again.
I would like to control the direction of a small (toy) DC motor by applying different voltage levels to it.
The motor is to be used on an outdoors rotor.
The rotor will control the direction of a small magnetic loop antenna.
There will be an RF preamplifier for the loop near the loop.
The whole...
I have a Collins KWM2-A HF transceiver for service (early model, schematic attached) and I wonder if the AGC can be made to have slower decay by a simple modification.
Collins has released some modifications and included them in the later models. However all of these require serious work to be...
First page of this PDF describes a way to stabilize the voltage to the VFO of the Collins KWM2-A, so that it is not affected by the lowering of the voltage during transmit from the otherwise unregulated PSU.
First picture shows the original circuit (just a voltage divider) and second picture the...
I thought just to keep the "tube character" of the machine. I do not know if this is a good idea though, cause I was always confused about the series resistors to be used and I do not know the current drawn by the VFO of the transceiver.
Hi, a Collins KWM2-A I service (1st schematic) does not have stabilized voltage on the VFO and during transmit (where more current is drawn and voltage gets lower) the frequency changes a bit. This is a known problem and fixed on later serial numbers with the zener circuit (2nd schematic).
I...
Hi,
Does the 2N3924 contain or have exposed BeO to worry about?
https://datasheetspdf.com/pdf-file/642416/NXP/2N3924/1
The datasheet states BeO only for the 2n3926 and 2n3927, am I reading this right?
Thank you
Hm... I see. If the bias is that critical in the signal amplification then this would be a problem. You see, class AB amplifiers have bias to avoid intermodulation distortion, but I want to do a different thing. That is have a class C amplifier biased to behave more like a B one. Or the other...
That's interesting! Of course, going more and more towards class-A should reduce the threshold.
That might sound trivial, but is it enough to use a variable resistor connected like this, to the bases of these complementary amplifiers, so as to achieve that?
I will try to simulate that, but I...
Thank you, I understand what you mention. This is a special case I do not care that much about the distortion, IMD. What I care the most is about achieving that low threshold, or "knee" where amplification will cease.
Hello,
I am trying to achieve the next:
Having an HF amplifier that can amplify incoming antenna signals, ONLY higher than a preset signal level. All signals below that preset level should be ignored.
I have achieved this behaviour with a class-C amplifier but this one works only on very high...
By experimentation, I came up with 2 useful points:
1. Even if I increase the level of my generator, the scope cannot cope with it on high frequencies. I think it has to do with input saturation of the vertical amplifier? So obviously a preamplifier is not the way to go.
2. But I thought, how...
I have made a 60's combo Tek 564 scope with Tek 3A6 and Tek 3B4 plugins. Despite the 3B4 specs are 20MHz triggering, it can trigger ok on 30MHz.
The 3A6 can show a 30MHZ signal, but the level of the signal is reduced much of course, since this is a 10MHz vertical plugin.
In fact the flatness of...
I have been experimenting with HV PSUs and I found that in a classic transformer - bridge rectifier PSU, one can remove the electrolytic filter capacitors if he includes a relatively large inductor after the bridge.
Here is my LTspice simulation, with the cyan line to represent the DC output.
I...
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