audio-talk

OK I have found a 2a3 (but substituded with 6b4g made in USA) an operating point pushing the dc current past 50mA to 54mA (the higher the current the lower the distortion) with the almost the same 2hd 3rd 4th and thd as the 300b output stage.

Paying attention to Nick’s point and Simon’s idea of ...

Yes Nick I looked at that with the 6b4g but the distortion was considerably more than the output stage.

So that, and the roll off in bass with inductance limitation not favoured, I looked at the srpp, then decided to make the srpp out of el36’s for heater simplicity; hoping the distortion is tamed ...

At last I have mounted which valve bases that I have. Had to order 8 different octal bases that I hope will fit the holes punched originally for Jumbo 4 Pin. Always loads of patience required for things to arive. But a mental victory that I began.

https://i.postimg.cc/j5t8hFQt/IMG-0612.jpg

The ...

I cant be exact about the distortion of any srpp as both valves are the load for each other and that is not known in my brainbox, but its a lot bigger load than 3k. So Its a question of try it and see how it sounds.

It would reduce inductance which is barely enough at 50mA. But to get the same distortion as the output valve it would require 100mA. So inductive is a non starter due to the poor distortion of the driver were it a 300b on a inter trans or a LCL.

Here is the 6b4g option. The distortion is ...

The EL36 SRPP worst case scenario 2nd h 3.2% drive impedance 150 ohm.

Unfortunately the AE interstages are limited to 50mA dc and the 300b at 50mA is not any more linear than the EL36 triode connected which is 4.2%.

https://i.ibb.co/LDSFqGvZ/IMG-2700.png

So the next plan, since the pl36’s only cost £15 each and I have sufficient. A pl36 srpp driver is back on the ...

Maybe its better to drive 300b with 300b, with which the inductive reactance of the AE interstages are better matched, if both levels of 300b have same operating point the distortions should cancel. 2.63 2nd h drives 2.63 2nd harmonic out of phase. The ecc88 shouldn’t add much distortion.

Also ...

Although the 300b distortion is 2.73% the EL36 driver is 4.2% 2nd, however the 6b4g isn’t better. You have to get the 801@ out the drawer and dust it off but then you have other challenges which means you end up considering not worth it except for driving a powerful efficient and lower distortion GM ...

Anyway, if I build it.

https://i.ibb.co/tMWGpPzR/IMG-2692.jpg
https://i.ibb.co/Zz8VV2mD/IMG-2690.jpg
https://i.ibb.co/sprHL6z4/IMG-2678.jpg

The power transformer may accept the current of the output valve only as it is 0.32 of the 360 which it ins meant to rest 10 minutes, work 5 minutes. I ...

But I’m open to offers for VT4C’s 833a’s V1505’s/4212’s/A300’s and some of my GM70’s, of which only four are copper which would be last to go. A pair of GM100’s.

https://i.ibb.co/XrcDNQ9L/IMG-2671.jpg
https://i.ibb.co/tp8dHdTV/IMG-2666.jpg

https://i.ibb.co/NgVvCPPC/IMG-2674.jpg
https://i.ibb.co/hRCtV53J/IMG-2675.jpg

The four abreast holes forward of the valve bases, I’ll Araldite matt black mesh underneath so power resistorse can vent through them ...

Nice