A pair of 4P1L can be easily matched, so 4P1L PSE is a great cost-effective option to deliver +3W single-ended warm sound in A1. Having investigated filament bias, harmonic content, now is time to look at this configuration in a bit more detail.
I have at hand a nice LL1623/60mA which can be configured to 3KΩ:8Ω. After looking at the loadline here is what I think it should play well to deliver 3W:
- Va=250V, Ia=60mA, Vgk=-22.9V
- The pair of 4P1L will equate to mu=8, gm=12mA/V and Ra=690Ω
- Vg= 41.6 Vpp
A driver with some headroom to provide at least 80Vpp should be fine for this SE amplifier. Without looking at harmonic cancellation, this stage should deliver 3W at about THD=1%. Clearly proven that I will not readapt the 45 for A2 🙂
EDIT – 17th March 2013
Just realised after reading Imzen’s comment that the maximum Pa used is incorrect. 4P1L is a 9W device when triode-connected. So here is the correct loadline for a 5K OT:
As we can see, it’s better to run this valve in PSE as you will get just 1W in SE with 1.5% THD when biased at 220V/40mA…
Hi Ale,
I like the idea of cost effectivness of 4P1L :). I have a One Electron UBT-1 OT, 1600 ohm Zp, max 160 mA. How would this sound to you 4 of 4P1L (mu=8, gm=24mA/V, Rp=300ohm ) PSE @ 35 mA ( sweet spot)each, total 140mA. A little challenge on filament supply.
Best,
Radu
Hi Radu,
That should work fine! I listened to a pair and sounds very clean and bright. A quartet should be easy to do.
Filaments in DC are not a challenge at all if you are using Rod Coleman’s regulators. I’m running my 4-65a which are 3A with less than 1mV noise!
Reach out to Rod and tell him you spoke to me regarding these high current DC filament regulators. Rod is very helpful and regulators are cost effective. Worth the change and once you use them With DHTs there is no return!
Cheers,
Ale
Couldn’t buy a brand-name OPT so I decide to wind a pair myself. I see some schematic using 2.2K for primary impedance but I haven’t got the inductance. Could you pls advise how many H need for pair of 4P1Ls PSE? Thanks
HI Imzen,
Primary inductance has to at least satisfy 2*pi*f*Lp >> Zaa. If Zaa is 2K2 then at very low frequencies (e.g. 10Hz) Lp >> 35H. It all will depend whether you could build an OT with ideally 90H for good bass performance.
Cheers,
Ale
Hi Ale,
Thanks so much for the formular.
But it’s seems 35H for an SE-OPT with normal silicon lamination is so hard to achieve. Therefore, I decide to cut low freq at 25Hz, hope that my OPT can reach Lp=14H. 😀
Thanks again!