audio-talk

OK Chatting to Victor at Victors Vintage on Falsgrave Rd Scarborough.

https://i.postimg.cc/9QWgXtvV/IMG-1692.jpg


It turns out that this valve line up is where I have returned. The whole push pull 300b idea gets me 20 watts. But so does an SE GM70.

With this simpler circuit the GM70 ...

I bought a d&r electronic mm phono stage. Broadcast quality for £75 on ebay. Best phono stage Ive ever auditioned at home. I had upgraded ear phono stage, the wad phono stage, some cheap ecc83 phono stages, and one fet phono stage oh and I built True Realism phono stages. Out of all those the only ...

The 2nd h at the 27 operating point is 1.5%.

So thats the line up per channel one 27 one 6J5 two 6b4g pp two 300b pp.(I have another Nightingale top plate punched so that may take all the signal stuff, but I dont know where its plinth is. But could get a plinth made. Though it may turn up.)
Have ...

So the 3rd harmonic of the 6b4g is 0.11

Not only have the 50k rule been neglected but perhaps many circuits are shortening the life of the valves through paracitic oscillation neglected.

I think you are tilting at windmills there. The minimum grid resistance will be in the case of fixed bias, and why would any oscillation due to ...

With a bias of 63v the PX4 or 6b4g on my investigations so far are optimal. 0.1 3rd h.

6J5 poor but mainly because the choke load Id be using was wound for el34.

I am happy I can use 6b4g. 10y wasnt quite as good and anyway wouldnt match the choke.

So My linup looks like 27 to 6j5 concertina to ...

That means in my case I have to check 3rd h at every stage, which is fortunately only the driver and the output stage. So the driver must operate in it’s sweet spot and not run into its dubious zone, so in PP that exceeding the bare minimum to keep driving the 3rd will get nasty. In short, more head ...

The 300b looks OK for 20 Watts class A1 push pull.

https://i.ibb.co/HVHwRj2/IMG-1818.png

I looked at the px4, 8 watts. I’ll not do that.


For Max searching out lowest PP distortion.

The operating point if the amp with 8k peak to peak transformers only stands if the loudspeakers are 8ohm. My ...

I like the way Marco explained the turns ratio of the OPT you might have wound yourself in those days.

https://i.ibb.co/7QsbV9w/IMG-1820.png

Both manufacturers recommend “automatic bias”

I have seen somewhere but cant find it, the max grid resistance for PX25 like WE.state for the 300b 50 k ...

I like the way Marco explained the turns ratio of the OPT you might have wound yourself in those days.

https://i.ibb.co/7QsbV9w/IMG-1820.png

Both manufacturers recommend “automatic bias”

I have seen somewhere but cant find it, the max grid resistance for PX25 like WE.state for the 300b 50 k ohm.

On the 10k grid stoppers Marconi showed with the PX4, Osram on the PX25 showed 5k which Osram termed Oscillation Stoppers. Osram also represented the capacitance in doted line the stopper is to prevent oscillation because of. Note also Osram have levelled thier circuit around the coupling ...

The 300b looks OK for 20 Watts class A1 push pull.



I looked at the px4, 8 watts. I’ll not do that.

10k px4 grid stoppers are suprising and 100ohm anode resistors. But ignore Markoni suggested methods is very brave.

So my way of turning PP is how Marconi advised a PX4 output stage. I’ll use a pair of lower impedance valves for the drivers as the OPT doing the centre tapped role wont be designed for the 6J5/L63.

But this is the way through without spending on quality SE output transformers.

https://i.ibb.co ...

Meanwhile I’m considering going the other way round, using the Sowter 8K peak to peak transformers, and using the PP output transformers from Steves EL34 amp I bought from him as cetre tapped chokes.