If I want to get -6.20v, I need to have a loop over gang extremes like so:
I soldered wire directly over it and max was -2v...
Look like that it was more or less probem with the wire going directly over common terminal... picking up interfernce from b+ or something...
Right now I'm getting -7v with wire like this:
Will shorten it more to see what happends.
EDIT:
It's good, working fine like that:
Triode's grid: -7v
Pentode's grid: -7,4v
Last edited:
Looks good to me too.
No, I will start with the audio section in the evening, when I get from work.
Can I build eveything? I remember we were talking about leaving pentode unpowered...
Yes. We shall need some kind of microphone. It may be a little speaker (the higher its impedance, the better), a headphone from portable music device (walkman, old mp3 player, cell phone) or a electret of any kind. Also a volume control (or modulation index control more properly called here) to adjust the gain of the audio path.
Having in mind what we have at junk, we shall adapt our project to those pieces.
Good job.
Having in mind what we have at junk, we shall adapt our project to those pieces.
Good job.
Ok...
100k pot for modulation index control, if it's good?
What you think would perform better, old phone mic from it's earpiece or modern mic from pc headphones?
Ham radio often uses what is at hand. When at home, use thr oscilloscope to find between all you have, the one with maximum sensitivity. Talk some words to it viewing the output amplitude and choose the one with the bigger output signal. If its too little, we can make a preamp with the ECC88.
Don't worry, I'm a MOT inspector, I work on demand... when we have no work, we can do wathever we want...
I had made the audio section...
I still need to add connector for mic and pot, but everything else is finished.
Only measurement I did was on balast there is 270v on both sides.
Is 270v to high for B+?
I must test the sensitivity of microphone tomorrow.
Just to be on the safe side... I can connect potentiometer as ussual, wiper to the amp input, low to ground and high to mic, right?
I still need to add connector for mic and pot, but everything else is finished.
Only measurement I did was on balast there is 270v on both sides.
Is 270v to high for B+?
I must test the sensitivity of microphone tomorrow.
Just to be on the safe side... I can connect potentiometer as ussual, wiper to the amp input, low to ground and high to mic, right?
Which is the pentode's cathode voltage? And triode's cathode and plate voltages?
The DCR of the choke is usually under 100 ohm, so the voltage drop will be low too. DC voltage drop is unimportant, we are interested in the audio voltage drop. We can call it now the modulation choke.
If you have a signal generator, thus use it to check the gain and the linearity of the amplifier. Load the audio amp with a 3~5 Kohm @2W resistor in parallel to the choke to simulate the modulated amplifier load. Hook the oscilloscope AC coupled to PCL86 pentode plate and see where is it clipping or not. Perhaps we need to touch some parameters. If not a signal generator, use line voltage steped down with a transformer and filter out the majority of the thrash that comes with it: build a simple low pass filter with a series 100K resistor and a 0.1uF shunt capacitor. From it you will have a reasonably clean 50 or 60Hz sine signal.
Of course. Nothing new here. When the audio section be connected to the PCF802 and it be doing its job, we shall call it the modulator.