audio-talk

If I have the numbers right, output impedance for a common cathode amplifier is RL || ra where || in parallel with. If the cathode is unbipassed, the anode resistance is increased by ra' = ra + RK( 1 + µ ) Richard, the choke size matters, as the anode resistance of the valve forms a RL high pass fil...

No, the cathode resistor would need to be the same value as the anode one.

Graeme wrote:They will be when its finished

The hum was a prediction rather than a reality

In that case my suggestions are a prediction as well

At the moment i have nothing between signal and grid (ie capacitors) is that good ?

Its not bad

Check the earthing. Are the relays being fed with a clean DC supply?

It could be, but the sheet Max was refering to talked about grounding one pin, and the answer was based upon that.

I guess the diodes are to prevent back EMF, but nt sure if they are needed here, they are normally used to stop killing a transistor driver, but as this is driven by a switch not sure about the point. I didn;t use them, low voltage signal diodes are fine. I would not bother with a resistor, just use...

I think the front end of Daves 2a3 would have the circuit you want. I do feel I should point out that the output stage in question is a nice idea, but does have some drawbacks, it can ONLY work in class A, the moment one valve gets to cutoff the output degrades badly. Thats fine, if you get enough p...

But as long as the heater winding is not connected to 0v anywhere, then the AC current will still go back down the twisted pair to the windings, so will cancel. You will still have the electrostatic field, but the electromagnetic one will cancel. Eek no mustn't, heater supply must connect to circui...

Its a mewasure of the power coil will draw when activated. 150mw @ 5v = 30ma

30ma * 5v = 0.15W

And so on

I * V = P

I = P / V

Yep, those will work, I would reduce the voiltage to 5v for a 5v relay.

I went for the ones I did as they have the lowest minimum voltage ratings, as I thought that is what we are interested, their low level operation.

You can model the front of the power supply, and a single leg, then insert a current tap to simulate the other leg. I would not worry about expensive caps, worry about that later, or just bipass the last ones in the supply with film caps. Also with the tolerance of electro caps, don;t fret too much ...

I used the tyco MT2 range for my pre, seems to have a lower minimum switching voltage than the ones WD use, (or at least used), RS have them and the data sheets, its simple enough to wire them via the selector switch to a regulated 5v supply created from the heater supply. If you want to switch the ...

25% is a good rule of thumb, but it depends if you know what the actual peak voltage is going to be, its possible to cerate power supplies where the peak could be 50% higher than the constant value, PSD can help you with this. Another thing to check is the ripple current rating. Electrolytics above ...

So following that argument, is the signal "seen" on the second grid always a perfect invert of the input signal, or are there any distortions introduced anywhere? If not, then it would seem to be the perfect phase splitter. If the CCS is perfect and the valves are perfect, the yes, its pe...