audio-talk

I tried 8k between choke mid point and G2 and it made no difference to the shape of then output.

I'll set UL aside to maybe come back to in a few years when I understand more.

It's not great is it - but is D3a in ultra-linear supposed to be any better than output valves are in ultra-linear, ie. not very linear ? Is the gain 200+ as you said, so that would be 20V Pk out ( is that Pk to Pk ? ) A few odd-order distortion products could produce that. 100mV peak, 14.7Vpk out....

Planning my phono stage and I'm reading Merlin Blencowe's book. I'm considering

SUT 1:20
D3a triode
01A
112 long tailed pair into LL1660 for balanced output

That would appear to lend itself to 2 stage RIAA. Any views compared to single stage?

It's not great is it - but is D3a in ultra-linear supposed to be any better than output valves are in ultra-linear, ie. not very linear ? Is the gain 200+ as you said, so that would be 20V Pk out ( is that Pk to Pk ? ) A few odd-order distortion products could produce that. 100mV peak, 14.7Vpk out....

I've never used ultra linear before, only trying it on suggestion from Jac (and while I have everything accessible for experimentation).

Band limit the input ... Translating that as a low pass filter on the input limiting to say 20Khz?

Ok I'll work on that for fun and learning.

IslandPink wrote: ↑Fri Jul 16, 2021 5:46 pm What's the frequency ?

1KHz square wave, 100mV pk input

Made some time to continue the experiments with the D3a today. Having got triode and pentode mode working I wanted to try ultralinear, suggested by Jac of JacMusic. Choke load, LL1667-20mA (200H). The two coils of the LL1667 are connected in series (correct polarity observed), anode connected to out...

Nick wrote: ↑Tue Jul 13, 2021 9:03 pm

Paul Barker wrote: ↑Tue Jul 13, 2021 7:34 pm anyone here with ability to check match got two surplus d3a to sell?

I can probably find a couple for you.

Let me know if you're struggling I have spare pairs bought from jacmusic

I found that a 6.3v output drawing 0.315A required the input voltage to be set at 11v. If course as Nick says with a pre-reg I don't need the diodes at the front of the board and thus I have 2 diode drops. As the DC boards are built and ready I'll just accommodate that extra drop in the supply. If ...

Nick wrote: ↑Tue Jul 13, 2021 8:51 am 1. No, other than the bridge and caps at the front are unneeded
2. No, maybe two ceramic caps on the inputs to the reg to chassis to get rid of any rf picked up in the cable.
3. As long as the output are not connected.

Thanks Nick

I recently bought a bench power supply and last night I tried using it to feed the input to one of Andrews excellent DC boards. Partly because it makes my bench less messy than transformers and wires and partly because I wanted to set the voltage going in. I found that a 6.3v output drawing 0.315A r...

Can you remind me Andrew, do your boards have a trimmer for fine tuning the output ? Yes, but I also keep saying trimmer pots are rubbish, and not to use them. Sadly, I am often ignored ;) However, if it's a prototype then I'll excuse you. I would add that putting the trimmer on the board is easy h...

Cap applied between G2 and cathode. Gain is now 215.

Thanks.

Nick wrote: ↑Sun Jul 11, 2021 6:07 pm Whatever gives you -3db with the g2 resistance in parallel with the load resistance.

Thanks Nick. My humble apologies for asking without doing my own research. Boooo

"The Valve Wizard -Small Signal Pentode" http://www.valvewizard.co.uk/pentode.html

Nick wrote: ↑Sun Jul 11, 2021 3:18 pm You need to decouple g2 to ground or the cathode with a cap so the voltage stays constant.

Ok thanks Nick. What value cap is normal?