Michael Koster said:
Thank you Michael; I miss that vibration testing stand I used in our laboratory 30 years ago. However, management did not know that we used it (very expensive peace of equipment) after hours when were tempted to make a PCB as fast as possible, otherwise it was needed to ask ladies in a chemical laboratory, and even bring them a chocolate to get it faster, out of a queue. 🙂
I still want to build some out of a speaker motor, but catastrophically have no time.
Heating is fine today outside, so it is done already. I'm going to solder it tonight. I was afraid that my FeCl is already exhausted, but it appeared to be fine.
Power supply board is ready to mount. You may see orientation of heat producing devices. Path for convection is open; the biggest capacitor will be on bottom of the box, so it's temperature will be minimal.
Since it is a prototype, for convenience the PCB will be mounted on small hinges, along the side where multi-stranded wires will go.
The power switch is on the front panel of the tube compartment, so wires to it should go through a shielded cable, right?
Wavebourn said:
I like the idea of 3-d construction. Is the PCB hinged to make it easier
to probe?
I want a scorpion soldering vise! I can make one. Are the "antennae"
flexible so you can position the clips? The tail looks like a hard to find
item...
Cheers!
Michael
Thanks gentlemen!
When I saw that Scorpio as a poster holder in some store I immediately understood how convenient it may be to solder XLR and TRS cables. 😉
Hinges were made for easy tweaking of the prototype.
3-d construction reflects the name: "Tower". This compartment will be mounted on top of the amp, with tall narrow heatsink on it's back.
When I saw that Scorpio as a poster holder in some store I immediately understood how convenient it may be to solder XLR and TRS cables. 😉
Hinges were made for easy tweaking of the prototype.
3-d construction reflects the name: "Tower". This compartment will be mounted on top of the amp, with tall narrow heatsink on it's back.
This scorpion is convenient when soldering plugs to cables. You can see one more poster holder on the picture:
Testing output tube stage of one channel: gyrator loaded triode strapped 6P15P.
Input signal: 4V P-P, output signal: 150V P-P, frequency: 300 KHz.
F-3db1=4 Hz, F-3dB2=900 KHz.
Is it enough, what do you think, to drive MOSFET follower?
Input signal: 4V P-P, output signal: 150V P-P, frequency: 300 KHz.
F-3db1=4 Hz, F-3dB2=900 KHz.
Is it enough, what do you think, to drive MOSFET follower?
Output tubes in both channels work equally well. I did not even try to match tubes, but they give the same amplification factors being loaded on gyrators, with LEDs in cathodes.
Ok, one tube channel is done, feedback loop closed.
I had to replace 6N2P by 6N1P to deal easier with Miller capacitance of triode strapped 6P15P, otherwise some dynamic phase shift would be introduced.
On pictures: 100 KHz triangles, 1.5V peak input, 120V swing output (95V swing will be needed actually on the peak output power).
I will need to decrease a coupling capacitor to stop 1 Hz ringing on transients.
I did not show noises now because when the cover is open some 400 KHz garbage is well visible, about 2 mV (-76 dB level). There will be a common cover, and a smaller one for an input tube. After that I'll check how noisy it is.
I had to replace 6N2P by 6N1P to deal easier with Miller capacitance of triode strapped 6P15P, otherwise some dynamic phase shift would be introduced.
On pictures: 100 KHz triangles, 1.5V peak input, 120V swing output (95V swing will be needed actually on the peak output power).
I will need to decrease a coupling capacitor to stop 1 Hz ringing on transients.
I did not show noises now because when the cover is open some 400 KHz garbage is well visible, about 2 mV (-76 dB level). There will be a common cover, and a smaller one for an input tube. After that I'll check how noisy it is.
I decreased a coupling capacitor 10 times, but it did not stop strange oscillations. The amp itself if innocent: a 14 Henry choke and 270 micro Farad capacitor made a good tank...
The problem was solved by adding one 2.2 micro farad film capacitor after a diode rectifier, before a choke. Now going back to the amplifier: PS problem had been solved. This is the example of creating new problems by solving former ones: in order to reduce diode currents and ripples I used LC filter that created new problems on frequencies way below rectified 120 Hz.
Probably a better idea would be to use a shunt regulator in case of LC filter, but for this prototype I am not going to redesign the power supply completely.
Probably a better idea would be to use a shunt regulator in case of LC filter, but for this prototype I am not going to redesign the power supply completely.
Here is 500 KHz 100V P-P response with 6N2P input tube, looks highly asymmetrical (for my taste). However, it is way above officially accepted audio band, but anyway it is a symptom that indicates presence of some non-linear phase shifts. Since subconscious sensitivity to phase shifts is 1,000 times better than a conscious one let's improve it anyway. The less of distortions we add is the better.
Here is the same 100V P-P, 500 KHz square, but with 6N1P tube. Looks much better, except some overshoots. Now, even way beyond officially accepted audibility the amp performs much better:
